Microbiology PDF Download – Parker et al. (OpenStax) BS Biology

Microbiology is the OpenStax textbook for a university microbiology course, written by senior contributing authors Nina Parker, Mark Schneegurt, Anh-Hue Thi Tu, Brian M. Forster and Philip Lister with a team of contributing authors, and you can download it free as a PDF from the official OpenStax site. Its 26 chapters run from the history of microbiology, microscopy and the cell, through bacteria, archaea, fungi, protists, helminths and viruses, to metabolism, genetics, antimicrobial drugs, immunity and infectious diseases arranged by body system.

The book was produced with the American Society for Microbiology and written for a single-semester course for non-majors with a focus on allied health, which makes it a natural fit for BS Biology and health-related degrees. This page gives a summary, key points, a tip, a common mistake and two practice questions for every chapter, plus a study plan, so you know what to read first before you open the official book.

Book Overview

Chapter List

Chapter 1: An Invisible World

Difficulty: Easy · Key topics: microbes, fermentation, germ theory, Leeuwenhoek, Golden Age of Microbiology, taxonomy, binomial nomenclature, three domains, types of microorganisms

The opening chapter asks what people knew about microbes before anyone could see them. It covers early uses of fermentation for beer, bread, cheese and wine, ancient ideas about disease and contagion, and the birth of microbiology with Antonie van Leeuwenhoek’s observations in 1675 and the Golden Age of Microbiology (1857–1914) of Pasteur and Koch. It then explains taxonomy, from Linnaeus and binomial names to Whittaker’s five kingdoms and Woese’s three domains, and ends with a tour of the main groups of microorganisms: bacteria, archaea, protozoa, algae, fungi, helminths and viruses.

Key Points:

• Microorganisms are living organisms that are generally too small to be seen without a microscope.
• Leeuwenhoek was the first to describe bacteria in 1675; the Golden Age of Microbiology ran from 1857 to 1914.
• Binomial nomenclature gives each organism a Latinized genus and species name, such as Homo sapiens.
• Carl Woese used small subunit ribosomal RNA to group life into three domains: Archaea, Bacteria and Eukarya.
• Bacteria and archaea are prokaryotes because they lack a nucleus, and no archaea are known to be human pathogens.
• Viruses are acellular and need a host to reproduce; helminths are included because their eggs and larvae are microscopic.

Memory Tip: Remember the taxonomic ranks with the sentence “Dear King Philip Came Over For Good Soup”: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species. A scientific name is just the last two words of that list.

Common Mistake: Writing a scientific name as “Homo Sapiens”. The genus starts with a capital letter, the species name is all lower case, and the whole name is italicized.

Important Questions:

• What did Woese and Fox use to construct their phylogenetic tree? They used small subunit ribosomal RNA sequences, which led to a tree with three domains: Archaea, Bacteria and Eukarya.
• What are the differences between bacteria and archaea? Both are prokaryotes, but they differ in evolutionary history, genetics, metabolic pathways, and cell wall and membrane composition. Archaea live in nearly every environment, including extreme ones, and none is known to cause human disease.

Chapter 2: How We See the Invisible World

Difficulty: Medium · Key topics: properties of light, refraction, magnification, resolution, brightfield and phase-contrast microscopes, fluorescence, electron microscopy, Gram stain, acid-fast stain

This chapter explains the physics and the tools behind seeing microbes. It starts with how light is reflected, absorbed, transmitted and refracted, how lenses focus it, and how magnification, resolution and contrast differ. It then follows the history from Hooke’s cells and Leeuwenhoek’s simple microscopes to the compound microscope, and compares brightfield, darkfield, phase-contrast, fluorescence, confocal, electron and scanning probe microscopes. The last section covers specimen preparation: fixation, Gram, acid-fast, capsule, endospore and flagella stains, and preparation for electron microscopy.

Key Points:

• Resolution can be improved by using a shorter wavelength, a lens with a larger numerical aperture, or stains that increase contrast.
• A simple microscope has one lens; a compound microscope has several lenses.
• In a brightfield microscope the condenser lens focuses all the light rays on the specimen to maximize illumination.
• Electron microscopes focus electrons with magnets: TEM needs very thin sections, and SEM needs samples coated by sputter-coating.
• Scanning probe microscopes, the STM and the AFM, reach even higher magnification by measuring feedback from a sharp probe.
• Acid-fast staining (Ziehl-Neelsen or Kinyoun, with carbolfuchsin) picks out cells with waxy mycolic acids in their walls.

Memory Tip: Remember the Gram stain order as crystal violet, iodine, alcohol, safranin. Gram-positive cells keep the first color (purple); gram-negative cells lose it and take the last (pink).

Common Mistake: Mixing up magnification and resolution. Making an image bigger does not make it clearer; resolution, the ability to tell two close points apart, is what limits what you can see.

Important Questions:

• What is the function of the condenser in a brightfield microscope? The condenser lens, below the stage, focuses all the light from the illuminator onto the specimen to maximize illumination. Its position is set once and should not be used to adjust brightness.
• How could you tell whether a bacterial sample contains cells with mycolic acid-rich cell walls? Use an acid-fast stain. Cells with waxy mycolic acids keep the red carbolfuchsin after the acid-alcohol decolorizer, while other cells lose it.

Chapter 3: The Cell

Difficulty: Medium · Key topics: spontaneous generation, Pasteur’s swan-neck flask, cell theory, endosymbiotic theory, germ theory, prokaryotic cell structures, cell wall, endospores, eukaryotic organelles

The Cell links the history of ideas to cell structure. It traces spontaneous generation from Aristotle to Redi, Needham, Spallanzani and Pasteur’s swan-neck flask, then cell theory, endosymbiotic theory and the move from miasma to germ theory with Semmelweis, Snow, Lister and Koch. Two long sections compare cells. Prokaryotes have a nucleoid, plasmids, 70S ribosomes, endospores, a plasma membrane and a cell wall, plus glycocalyces, pili and flagella. Eukaryotes have a nucleus, 80S ribosomes, an endomembrane system, a cytoskeleton, mitochondria, chloroplasts, cilia and flagella.

Key Points:

• Pasteur’s swan-neck flask experiment disproved spontaneous generation and supported the idea that life only comes from life.
• Endosymbiotic theory says mitochondria and chloroplasts descend from bacteria; their ribosomes and division by binary fission resemble those of bacteria.
• Gram-positive cells have a thick peptidoglycan layer; gram-negative cells have a thin layer surrounded by an outer membrane.
• Archaeal membranes contain ether-linked fatty acids, while bacterial membranes contain ester-linked fatty acids.
• Prokaryotic ribosomes are 70S; cytoplasmic eukaryotic ribosomes are 80S.
• Some bacteria form endospores to survive in a dormant state and germinate when conditions improve.
• Mitochondria have two membranes, with cristae on the inner one, and are the site of cellular respiration.

Memory Tip: Remember 70 and 80: prokaryotes have 70S ribosomes, and the larger eukaryotic cell has 80S ribosomes. Mitochondria and chloroplasts carry 70S ribosomes, which is a clue to their bacterial origin.

Common Mistake: Assuming mitochondria and chloroplasts have the same 80S ribosomes as the rest of the eukaryotic cell. Their ribosomes are 70S, like those of bacteria.

Important Questions:

• Explain Pasteur’s swan-neck flask experiment. Pasteur boiled broth in flasks with long, curved necks. Air could enter, but dust and microbes were trapped in the bend, so the broth stayed clear. It spoiled only when the neck was broken, showing that microbes come from other microbes and not from nonliving matter.
• What evidence supports the endosymbiotic theory? Mitochondrial and chloroplast ribosomes are structurally similar to bacterial ribosomes, these organelles divide by a process that strongly resembles bacterial binary fission, and bacterial endosymbionts are seen in modern eukaryotic cells.

Chapter 4: Prokaryotic Diversity

Difficulty: Medium · Key topics: habitats, microbiome, symbiosis, Proteobacteria, spirochetes, CFB group, cyanobacteria, gram-positive bacteria, Actinobacteria, Clostridia, archaea

Chapter 4 surveys the main groups of bacteria and archaea. It begins with habitats, metabolic flexibility, symbiosis, the human microbiome and microbiota, and classification by staining and molecular genetics. It then tours the Proteobacteria from alpha to epsilon, the nonproteobacteria gram-negative and phototrophic groups (chlamydia, spirochetes, the CFB group, planctomycetes, purple and green bacteria, cyanobacteria), and the gram-positive bacteria, split into high G+C and low G+C groups. It closes with the deeply branching bacteria and the archaea, including methanogens and halophiles.

Key Points:

• Proteobacteria are gram-negative bacteria, identified by Carl Woese in the 1980s from nucleotide sequence homology, and are grouped into five classes, alpha to epsilon.
• Gammaproteobacteria are the largest and most diverse group and include Escherichia coli, a coliform enteric bacterium.
• Spirochetes are motile, spiral bacteria; some cause syphilis and Lyme disease.
• High G+C gram-positives (Actinobacteria) include Mycobacterium tuberculosis and Corynebacterium diphtheriae; low G+C groups include Clostridia, Bacilli, Lactobacillales and mycoplasmas.
• Clostridia are mostly obligate anaerobes that form endospores, such as C. tetani (tetanus) and C. botulinum (botulism).
• Only archaea are known to produce methane (methanogens), and halophilic archaea use bacteriorhodopsin for photosynthesis.
• Cyanobacteria produce oxygen and are thought to have played a critical role in forming the earth’s atmosphere.

Memory Tip: Link each group to one signature organism: Proteobacteria to E. coli, spirochetes to syphilis, high G+C gram-positives to tuberculosis, Clostridia to tetanus and botulism, and archaea to no disease at all.

Common Mistake: Calling archaea pathogens. They look like bacteria under the microscope, but no archaea have been identified as human pathogens.

Important Questions:

• What is the difference between commensalism and amensalism? In commensalism one organism benefits and the other is unaffected. In amensalism one organism is harmed and the other is unaffected.
• Why are the deeply branching bacteria important? They are phylogenetically the most ancient forms of life, closest to the last universal common ancestor. Many live in extreme environments like those of early Earth, so they help us understand evolution, and some are used in industry.

Chapter 5: The Eukaryotes of Microbiology

Difficulty: Medium · Key topics: protists, Amoebozoa, Chromalveolata, Excavata, helminths, nematodes, flatworms, fungi, algae, lichens

This chapter covers the eukaryotic microorganisms. Protists are described by nutrition, form, movement and reproduction, with key structures such as contractile vacuoles, cilia, flagella, pellicles and pseudopodia, and their groups Amoebozoa, Chromalveolata and Excavata, which include major parasites. The chapter then covers helminths, roundworms and flatworms (tapeworms and flukes), and fungi, with chitin cell walls, reproductive types and the four medically important groups. It ends with algae, including toxic blooms and the sources of agar and carrageenan, and lichens, the partnerships between a fungus and an alga or cyanobacterium.

Key Points:

• Protists are a diverse, polyphyletic group; they may be unicellular or multicellular, and some lack organelles such as mitochondria.
• Helminths are studied in microbiology because they are often identified by their microscopic eggs and larvae; the two major groups are roundworms (Nematoda) and flatworms (Platyhelminthes).
• Fungal cell walls contain chitin, and fungal membranes contain ergosterol, which is a target for antifungal drugs.
• Medically important fungi fall into Zygomycota, Ascomycota, Basidiomycota and Microsporidia.
• Algae are photosynthetic protists that supply agar, used to solidify microbiological media, and carrageenan.
• A lichen is a symbiosis between a fungus and an alga or cyanobacterium, currently seen as a controlled parasitism, and lichens act as indicators of air pollution.

Memory Tip: Think of ergosterol as the fungal version of cholesterol. Human membranes use cholesterol and fungal membranes use ergosterol, which is why some antifungal drugs can target fungi without attacking human cells.

Common Mistake: Treating seaweeds as plants. Large multicellular algae are not plants and lack plant-like tissues and organs.

Important Questions:

• What is the best defense against tapeworm infection? Avoiding undercooked meat. Tapeworms and flukes are often transmitted through undercooked meat, so cooking meat thoroughly is the best defense.
• What are three ways that lichens are environmentally valuable? Lichens help to create soil, provide food for other organisms, and act as indicators of air pollution.

Chapter 6: Acellular Pathogens

Difficulty: Medium · Key topics: viruses, capsid, envelope, bacteriophages, lytic and lysogenic cycles, transduction, latency, plaques, viroids, virusoids, prions

Chapter 6 deals with infectious agents that are not cells. It describes virus size (20 nm to 900 nm), structure (nucleic acid, protein capsid and sometimes an envelope), host range and shapes (helical, polyhedral, complex), and classification by morphology, nucleic acid, host and enzymes. It then follows the viral life cycle: attachment, penetration, uncoating, biosynthesis, maturation and release, the lytic and lysogenic cycles of bacteriophages, transduction, animal virus latency and the one-step growth curve. It also covers culturing and detecting viruses (plaques, cytopathic effects, PCR, hemagglutination), then viroids, virusoids and prions.

Key Points:

• A virion contains DNA or RNA, never both, inside a protein capsid, and some have a phospholipid envelope.
• Viruses are obligate intracellular parasites and usually have a limited host range.
• Infection follows six stages: attachment, penetration, uncoating, biosynthesis, maturation and release.
• The lytic cycle kills the host cell; in the lysogenic cycle the phage DNA integrates into the host genome.
• A bacteriophage growth curve is a one-step multiplication curve, not a sigmoidal curve like that of bacteria.
• Bacteriophages are detected as clear plaques on a lawn of bacteria; animal viruses are detected by cytopathic effects, PCR, enzyme immunoassays and serology.
• Prions are proteinaceous infectious particles that cause transmissible spongiform encephalopathies, resist heat, chemicals and radiation, and have no treatment.

Memory Tip: Lytic sounds like “lyse”, to burst: the host cell bursts and dies. In the lysogenic cycle the phage lies low inside the host genome as a prophage.

Common Mistake: Describing a virus as a tiny cell. A virion has no cytoplasm, ribosomes or metabolism of its own and cannot reproduce without a host cell.

Important Questions:

• What is the difference between the lytic and lysogenic cycles? In the lytic cycle the phage takes over the cell, makes new virions and lyses the host. In the lysogenic cycle the phage DNA integrates into the host genome and is copied along with it, leaving the host alive.
• What is the difference between generalized and specialized transduction? In generalized transduction any piece of chromosomal DNA can be packaged by accident into a phage head. In specialized transduction only DNA next to the prophage integration site is transferred, because of imprecise excision of the prophage.

Chapter 7: Microbial Biochemistry

Difficulty: Medium · Key topics: elements of life, isomers, functional groups, dehydration synthesis, carbohydrates, lipids, proteins, protein structure, MALDI-TOF, FAME and PLFA

Chapter 7 gives the chemistry that the rest of the book relies on. It lists the elements of living cells (hydrogen, carbon, oxygen, nitrogen, phosphorus and sulfur), explains how carbon skeletons, isomers and functional groups create different molecules, and how monomers join by dehydration synthesis. The next sections cover carbohydrates, lipids (fatty acids, triglycerides, phospholipids, isoprenoids and sterols) and proteins (amino acids, peptide bonds, four levels of structure, denaturation). The last section shows how lipid, protein and mass-spectrum profiles identify bacteria.

Key Points:

• Monosaccharides are classed by carbon number: trioses 3, tetroses 4, pentoses 5 and hexoses 6.
• Sucrose, lactose and maltose are disaccharides; starch and glycogen store energy and cellulose is structural.
• NAG and NAM are modified sugars used to build peptidoglycan and chitin.
• Fatty acids with no double bonds are saturated; phospholipids are amphipathic and form the bilayer of membranes.
• Protein structure has four levels, primary, secondary, tertiary and quaternary, and denaturation destroys the higher-order structure and the function.
• MALDI-TOF identifies a microbe from its mass spectrum, and FAME and PLFA analysis identify it from its lipid composition.

Memory Tip: Dehydration synthesis joins monomers and releases water. Linking the name to the result helps: dehydrate to join, and water comes out.

Common Mistake: Mixing up the two bonds. Peptide bonds link amino acids in proteins, while glycosidic bonds link sugars in carbohydrates.

Important Questions:

• What is the structure of a typical phospholipid, and is it polar or nonpolar? A phospholipid has hydrophobic, nonpolar fatty acid chains and a polar head group, so it is amphipathic. This lets it form bilayers with hydrophilic surfaces and a hydrophobic interior.
• How do MALDI-TOF, FAME and PLFA help identify microbes? MALDI-TOF matches the unique mass spectrum of an unknown microbe. FAME and PLFA analysis identify a microbe from the pattern of fatty acids in its lipids.

Chapter 8: Microbial Metabolism

Difficulty: Hard · Key topics: catabolism and anabolism, redox reactions, NAD+, ATP, enzymes, glycolysis, Krebs cycle, electron transport, fermentation, photosynthesis, biogeochemical cycles

This chapter explains how microbes get and use energy. It classifies organisms by carbon source (autotroph, heterotroph) and energy source (phototroph, chemotroph), then covers redox reactions, the electron carriers NAD+, FAD and NADP+, ATP, and enzymes with their active sites and inhibitors. It follows glucose through glycolysis, the transition step and the Krebs cycle, then the electron transport system and chemiosmosis, and compares fermentation pathways. It also covers lipid and protein catabolism, photosynthesis and the roles of microbes in the carbon, nitrogen and sulfur cycles and in bioremediation.

Key Points:

• Glycolysis does not need oxygen and gives two pyruvate molecules, a net gain of ATP by substrate-level phosphorylation, and NADH.
• Each turn of the Krebs cycle oxidizes one acetyl group and produces three NADH, one FADH2 and one ATP, and releases two CO2.
• Most ATP in respiration comes from oxidative phosphorylation: the electron transport system builds a proton motive force, and ATP synthase uses it.
• The electron transport system sits in the plasma membrane of prokaryotes and the inner mitochondrial membrane of eukaryotes.
• Fermentation uses an organic molecule as the final electron acceptor to regenerate NAD+ from NADH so glycolysis can continue; it has no electron transport system.
• Lipids are degraded by lipases and beta-oxidation, and proteins by proteases; both pathways connect to glycolysis and the Krebs cycle.
• In the nitrogen cycle, fixation converts nitrogen gas to ammonia, nitrification oxidizes it to nitrite and nitrate, and denitrification returns nitrogen gas.

Memory Tip: Use OIL RIG for redox: Oxidation Is Loss of electrons, Reduction Is Gain. NAD+ is reduced to NADH when it picks up electrons from food molecules.

Common Mistake: Saying that fermentation makes ATP on its own. Fermentation only regenerates NAD+ so that glycolysis can keep running; the small ATP yield comes from glycolysis.

Important Questions:

• What is substrate-level phosphorylation, and when does it occur? It is the direct transfer of a phosphate group to ADP to make ATP, without an electron transport system. It occurs in glycolysis and in the Krebs cycle.
• What is the relationship between chemiosmosis and the proton motive force? The electron transport system pumps H+ across a membrane and builds the proton motive force. Chemiosmosis is the flow of H+ back through ATP synthase, which uses that energy to make ATP from ADP and Pi.

Chapter 9: Microbial Growth

Difficulty: Medium · Key topics: binary fission, growth curve, generation time, plate counts, MPN, biofilms, oxygen requirements, pH, temperature, growth media

Chapter 9 describes how bacterial populations grow and what limits them. It covers binary fission, generation time, the four phases of the growth curve (lag, logarithmic, stationary, death) and ways to count cells: plate counts, membrane filtration, most probable number and turbidity. It also covers other division patterns and biofilms with quorum sensing. The chapter then sorts microbes by oxygen needs, pH (neutrophiles, acidophiles, alkaliphiles), temperature (psychrophiles to hyperthermophiles), salt, light and moisture, and ends with media: chemically defined, selective, enriched and differential.

Key Points:

• Generation time is the doubling time of a population, and most bacteria divide by binary fission.
• In a closed system, growth passes through lag, logarithmic (exponential), stationary and death phases.
• Obligate aerobes need oxygen, obligate anaerobes cannot grow with it, facultative anaerobes grow better with oxygen but can grow without it, and microaerophiles need less than 21% oxygen.
• Catalase, peroxidase and superoxide dismutase detoxify reactive oxygen species.
• Mesophiles grow best between about 20 and 45 °C, and pathogens are usually mesophiles.
• Selective media favor some microbes and inhibit others; differential media distinguish microbes by colony color or a change in the medium.
• Biofilms are communities enclosed in an extracellular polymeric substance, and their cells coordinate by quorum sensing.

Memory Tip: Match the prefixes to the temperature: psychro means cold, meso means middle, thermo means hot, and hyperthermo means extreme heat.

Common Mistake: Confusing selective and differential media. Selective media stop some organisms from growing; differential media let many grow but show differences, such as colony color.

Important Questions:

• Why measure the light transmitted through a control tube holding only broth when you measure turbidity? The broth control sets the baseline. It lets you subtract the effect of the broth itself, so the reading reflects only the cells in the culture.
• Why should Haemophilus influenzae be grown in a candle jar? It is a capnophile, an organism that grows best with more carbon dioxide and less oxygen than in air. A burning candle in a closed jar uses up most of the oxygen and releases CO2.

Chapter 10: Biochemistry of the Genome

Difficulty: Medium · Key topics: discovery of DNA as genetic material, Griffith, Hershey-Chase, nucleotides, Chargaff’s rules, double helix, RNA types, genes, chromosomes, noncoding DNA

Chapter 10 shows how microbes helped reveal that DNA carries heredity. It follows Mendel, Miescher, Morgan, Griffith’s transformation, Avery, MacLeod and McCarty, and the Hershey-Chase phage experiment, and explains why bacteria and viruses are good model systems. It then covers DNA structure (nucleotides, phosphodiester bonds, Chargaff’s rules, the antiparallel double helix, denaturation), RNA (mRNA, rRNA and tRNA, with uracil in place of thymine) and cellular genomes: genes, genotype and phenotype, chromosomes, supercoiling and packaging proteins, noncoding DNA and extrachromosomal DNA.

Key Points:

• A nucleotide is a pentose sugar, a phosphate group and a nitrogenous base; DNA has the purines adenine and guanine and the pyrimidines cytosine and thymine.
• Chargaff found that adenine roughly equals thymine and guanine roughly equals cytosine, which reflects complementary base pairing.
• The two DNA strands are antiparallel; one end of a strand has a free 5′ phosphate and the other a free 3′ hydroxyl.
• RNA is usually single stranded, contains ribose, and uses uracil instead of thymine.
• Prokaryotes are typically haploid with one circular chromosome in the nucleoid; eukaryotes are diploid with several linear chromosomes in the nucleus.
• Eukaryotes and archaea package DNA with histones, while bacteria use other DNA-binding proteins.
• Genotype is the set of genes a cell carries, and phenotype is the observable result of the genes in use.

Memory Tip: Remember CUT the Py: Cytosine, Uracil and Thymine are the pyrimidines, and the other two bases, adenine and guanine, are the purines.

Common Mistake: Thinking that A-T rich DNA is the harder to melt. G-C pairs have three hydrogen bonds and A-T pairs have two, so DNA with high GC content is harder to denature.

Important Questions:

• Why is DNA with a high GC content more difficult to denature than DNA with a low GC content? Guanine and cytosine form three hydrogen bonds per pair, while adenine and thymine form two, so more heat or chemical is needed to separate G-C rich strands.
• What does the term “antiparallel” mean for DNA? The two strands run in opposite directions: one runs 5′ to 3′ and its partner runs 3′ to 5′, with the sugar-phosphate backbones on the outside.

Chapter 11: Mechanisms of Microbial Genetics

Difficulty: Hard · Key topics: central dogma, DNA replication, transcription, translation, genetic code, mutations, horizontal gene transfer, conjugation, transposons, operons

Chapter 11 follows the flow of genetic information. It begins with the central dogma, then covers semiconservative DNA replication in bacteria (origin, gyrase, helicase, primase, DNA polymerase III, leading and lagging strands, Okazaki fragments, ligase) and in eukaryotes (telomeres and telomerase). Transcription with eukaryotic RNA processing, and translation with the genetic code, tRNA and the stages of the ribosome follow. The chapter then covers mutations and mutagens, horizontal gene transfer by transformation, transduction and conjugation, transposons, and gene regulation through operons such as lac and trp.

Key Points:

• The central dogma says DNA specifies mRNA, which specifies the amino acid sequence of proteins.
• Replication is semiconservative; the leading strand is made continuously and the lagging strand in Okazaki fragments, each needing its own primer.
• RNA polymerase needs no primer; eukaryotic mRNA gets a 5′ cap and a poly-A tail and is spliced.
• The genetic code is degenerate and almost universal; in prokaryotes the start codon codes for N-formylmethionine.
• Point mutations can be silent, missense or nonsense, and an insertion or deletion that is not a multiple of three causes a frameshift.
• Conjugation is mediated by the F plasmid, Hfr cells transfer chromosomal DNA, and R plasmids spread antibiotic resistance.
• The trp operon is a classic repressible operon and the lac operon is a classic inducible operon.

Memory Tip: Say “primase, polymerase, ligase” in that order for replication: primase starts the primer, polymerase extends the strand, and ligase seals the gaps.

Common Mistake: Calling every mutation harmful. A silent mutation changes the codon but not the amino acid; the damaging ones are frameshifts and nonsense mutations.

Important Questions:

• Why is primase required for DNA replication? DNA polymerase can only add nucleotides to a free 3′-OH group. Primase makes a short RNA primer that supplies it, and each Okazaki fragment on the lagging strand needs its own primer.
• Why are insertions or deletions usually more harmful than point mutations? Adding or removing a number of nucleotides that is not a multiple of three shifts the reading frame, which changes every amino acid after the mutation and usually gives a nonfunctional protein.

Chapter 12: Modern Applications of Microbial Genetics

Difficulty: Medium · Key topics: recombinant DNA, molecular cloning, restriction enzymes, blue-white screening, gel electrophoresis, Southern blot, PCR, genomics, gene therapy

Chapter 12 shows how microbial genetics became a toolkit. It defines biotechnology and recombinant DNA, then explains molecular cloning with restriction enzymes, ligase, plasmid vectors, blue-white screening, genomic and cDNA libraries and ways to transfect eukaryotic cells. It covers probes, gel electrophoresis, RFLP, Southern and northern blots, microarrays, SDS-PAGE and PCR, including RT-PCR and real-time PCR. It then covers genomics, transcriptomics, proteomics, metagenomics and bioinformatics, reporter genes, recombinant pharmaceuticals, RNA interference and gene therapy with its risks and ethical questions.

Key Points:

• Restriction enzymes cut DNA, ligase pastes fragments together, and plasmids are common cloning vectors.
• Blue-white screening selects bacteria that carry a recombinant plasmid, because the insert disables the reporter gene.
• A genomic library holds fragments of an organism’s genome, while a cDNA library represents the mRNA expressed in a cell.
• Agarose gel electrophoresis separates DNA by size; PAGE separates proteins by size, and SDS masks their native charge.
• A Southern blot finds a DNA sequence and a northern blot detects a particular mRNA.
• PCR amplifies a specific DNA sequence; RT-PCR detects mRNA expression and real-time PCR quantifies a sequence.
• Gene therapy shows great promise for genetic diseases but carries significant risks and ethical issues and is closely regulated.

Memory Tip: Walk through a cloning experiment as four words: cut (restriction enzyme), paste (ligase), insert (transformation), screen (blue-white). That sequence answers most exam questions on the topic.

Common Mistake: Mixing up the blots. A Southern blot detects DNA and a northern blot detects RNA; protein is separated by PAGE.

Important Questions:

• Why must the DNA polymerase used in PCR be heat-stable? PCR cycles through high temperatures to separate the DNA strands, so an ordinary polymerase would be denatured. A heat-stable enzyme survives every cycle.
• When would a scientist generate a cDNA library instead of a genomic library? When the aim is to study only the genes that are expressed in a cell at a given time, because a cDNA library is made from the mRNA molecules present in the cell.

Chapter 13: Control of Microbial Growth

Difficulty: Medium · Key topics: fomites, biosafety levels, sterilization, disinfection, antisepsis, heat, pasteurization, radiation, chemical disinfectants, phenol coefficient

Chapter 13 covers the practical control of microbes. It defines fomites, sterilization, disinfection and antisepsis, explains the four CDC and NIH biosafety levels, and classifies medical items as critical, semicritical or noncritical. It then covers physical methods (dry and moist heat, pasteurization, refrigeration, freezing, high pressure, desiccation, lyophilization, radiation) and chemical methods (heavy metals, halogens, alcohols, phenolics, surfactants, quaternary ammonium compounds and gases). It ends with tests of effectiveness: the phenol coefficient, the disk-diffusion method and the use-dilution test.

Key Points:

• There are four biosafety levels, set by an agent’s infectivity, ease of transmission and disease severity, plus the type of work.
• Disinfection removes potential pathogens from objects, antisepsis uses chemicals safe enough for tissue, and sterilization removes all microbes.
• Critical items touch sterile tissue, semicritical items touch mucous membranes, and noncritical items touch intact skin.
• Moist heat is more effective than dry heat because it penetrates cells better.
• HTST pasteurization suits milk that will be refrigerated, and UHT treatment suits milk for long storage without refrigeration.
• Alcohols work best at about 70% in water, because stronger solutions coagulate surface proteins too fast to enter the cell.
• High-level germicides can kill endospores, while intermediate-level and low-level germicides cannot kill all of them.

Memory Tip: Rank medical items by what they touch: critical (sterile tissue), semicritical (mucous membranes), noncritical (intact skin). The required cleanliness drops from sterilization to high-level disinfection to ordinary cleaning.

Common Mistake: Using disinfectant and antiseptic as synonyms. Disinfectants are for objects and may be too harsh for living tissue, while antiseptics are safe enough to use on skin.

Important Questions:

• Which solution of ethyl alcohol is more effective at inhibiting microbial growth, 70% or 100%? The 70% solution. Alcohols coagulate proteins, and in stronger solutions rapid coagulation of surface proteins stops the alcohol from penetrating the cell.
• What is the advantage of HTST pasteurization compared with sterilization, and of UHT treatment? HTST kills pathogens and reduces spoilage microbes in milk that will be refrigerated, without sterilizing it. UHT treatment allows milk to be stored for a long time without refrigeration.

Chapter 14: Antimicrobial Drugs

Difficulty: Hard · Key topics: magic bullet, penicillin, bacteriostatic and bactericidal drugs, spectrum, antibacterial mechanisms, antifungal and antiviral drugs, drug resistance, Kirby-Bauer, MIC

Chapter 14 explains how antimicrobial drugs work and why they fail. It starts with history: traditional remedies, Ehrlich’s magic bullet, Fleming’s penicillin and Domagk’s sulfanilamide. It then covers bacteriostatic and bactericidal drugs, narrow and broad spectrum, and dosing. The mechanism sections cover antibacterial targets (cell wall, 70S ribosome, membranes, nucleic acid synthesis, folic acid) and antifungal, antiprotozoan, antihelminthic and antiviral drugs, including HIV combination therapy. It ends with resistance mechanisms, disk-diffusion, MIC and MBC testing, and strategies for discovering new drugs.

Key Points:

• Antibacterial drugs rely on selective toxicity, targeting structures that differ between bacterial and human cells.
• Beta-lactams, glycopeptides and bacitracin block cell wall synthesis and leave cells open to osmotic lysis.
• Aminoglycosides and tetracyclines bind the 30S ribosomal subunit; macrolides, lincosamides, chloramphenicol and oxazolidinones bind the 50S subunit.
• Rifamycins block bacterial transcription and fluoroquinolones block DNA replication.
• Sulfonamides and trimethoprim interfere with folic acid synthesis.
• Resistance can come from drug modification or inactivation, reduced uptake or efflux, target modification, enzymatic bypass or target mimicry, and resistance genes spread on plasmids and transposons.
• In the Kirby-Bauer test, zones of inhibition must be compared with standards for each drug to judge susceptibility.

Memory Tip: Build a four-row table in your notebook: cell wall, protein synthesis, nucleic acids, metabolism. Add the drug classes of the chapter to the row that matches their target.

Common Mistake: Reading a bigger zone of inhibition as a stronger drug. Zone sizes must be compared against standards for each drug, and they do not allow a direct comparison of potency between drugs.

Important Questions:

• What is the difference between MIC and MBC? The minimum inhibitory concentration (MIC) is the lowest drug concentration that stops visible growth. The minimal bactericidal concentration (MBC) is the lowest concentration that kills the bacteria, typically found as a follow-up to the MIC in the tube dilution method.
• When is using a broad-spectrum antimicrobial drug warranted? For serious systemic infections when there is no time to identify the cause, when narrow-spectrum drugs fail, or to treat or prevent infections with several types of microbes.

Chapter 15: Microbial Mechanisms of Pathogenicity

Difficulty: Medium · Key topics: signs and symptoms, periods of disease, Koch’s postulates, virulence, opportunistic pathogens, stages of pathogenesis, exoenzymes, toxins, immune evasion

Chapter 15 asks how microbes cause disease. It defines infection, disease, signs and symptoms, communicable, contagious, nosocomial, iatrogenic, acute, chronic and latent disease, and the five periods of an illness. It covers Koch’s postulates and their molecular version, virulence measured by ID50 and LD50, primary and opportunistic pathogens, and the stages of pathogenesis from exposure to transmission. It then reviews virulence factors: adhesion, exoenzymes, endotoxin and exotoxins, capsules and other ways of evading immunity, viral antigenic drift and shift, and the virulence factors of fungi, protozoa and helminths.

Key Points:

• Signs of a disease are objective and measured; symptoms are subjective and reported by the patient.
• The five periods of disease are incubation, prodromal, illness, decline and convalescence.
• Virulence, the degree to which a pathogen can cause disease, is quantified by the ID50 or LD50.
• Opportunistic pathogens cause disease only when a break in the barriers or immunosuppression compromises the host.
• Endotoxin is the lipid A part of the lipopolysaccharide of the gram-negative cell envelope, while exotoxins are secreted proteins.
• Nosocomial diseases are contracted in hospital settings, while iatrogenic diseases are the direct result of a medical procedure.
• Influenza viruses avoid recognition by the immune system through both antigenic drift and antigenic shift.

Memory Tip: Order the periods of disease as I-P-I-D-C: Incubation, Prodromal, Illness, Decline, Convalescence.

Common Mistake: Mixing up signs and symptoms. A fever you can measure is a sign; a headache the patient reports is a symptom.

Important Questions:

• What is the difference between signs and symptoms of a disease? Signs are objective and can be measured, such as a fever of 38 °C. Symptoms are subjective and reported by the patient, such as nausea or a headache.
• How do helminths evade the immune system? They coat their outer surface with glycan molecules that make them look like host cells, or they suppress the immune system.

Chapter 16: Disease and Epidemiology

Difficulty: Easy · Key topics: morbidity and mortality, incidence and prevalence, endemic, epidemic, pandemic, John Snow, study types, reservoirs, vectors, healthcare-associated infections, WHO

This chapter introduces epidemiology, the science behind public health. It defines morbidity and mortality, incidence and prevalence, and the patterns sporadic, endemic, epidemic and pandemic. It reviews the pioneers John Snow, Florence Nightingale and Joseph Lister and the main study types: descriptive, retrospective, prospective, analytical and experimental. It then covers reservoirs and carriers, contact, vehicle and vector transmission, quarantine and healthcare-associated infections. It ends with the role of the CDC and the World Health Organization and with emerging and reemerging infectious diseases.

Key Points:

• Incidence is the number of new cases in a period, while prevalence is the total number of people affected.
• Sporadic diseases occur rarely, endemic diseases occur at a constant level, and epidemic and pandemic diseases exceed the expected level locally or globally.
• Contact transmission is direct (with an infected host) or indirect (through a fomite).
• Vehicle transmission carries an agent through a substance such as soil, water or air.
• Vector transmission is mechanical when an organism carries the agent on its body and biological when the organism is itself a host.
• Healthcare-associated (nosocomial) infections are acquired in clinical settings, where susceptible, immunocompromised people are concentrated.
• Emerging diseases are new to human populations or increasing, and reemerging diseases are resurging after being controlled.

Memory Tip: Incidence is the “incoming” new cases in a period; prevalence is everyone “present” with the disease at a given time.

Common Mistake: Using epidemic and pandemic as the same word. An epidemic is a larger than expected outbreak in a local area; a pandemic is one that spreads across the world.

Important Questions:

• What is the difference between incidence and prevalence? Incidence is the number of new cases during a specified period, while prevalence is the total number of cases in the population, both usually expressed as proportions.
• What are the two types of vector transmission? Mechanical, when a living organism carries the infectious agent on its body to a new host, and biological, when the organism is itself an infected host that passes the agent on.

Chapter 17: Innate Nonspecific Host Defenses

Difficulty: Medium · Key topics: skin and mucous membranes, microbiome, antimicrobial peptides, complement, cytokines, white blood cells, phagocytosis, PAMPs, inflammation, fever

Chapter 17 describes the body’s first line of defense. Physical defenses include skin, mucous membranes, endothelia, mechanical removal (shedding, mucociliary sweeping, coughing, peristalsis, flushing) and the microbiome. Chemical defenses include antimicrobial peptides, plasma proteins, acute-phase proteins, the complement system and cytokines. The chapter then describes white blood cells made by hematopoiesis, pathogen recognition through PAMPs and pattern recognition receptors, phagocytosis and extravasation, and inflammation and fever, including the five cardinal signs.

Key Points:

• Innate immunity is nonspecific and provides a first line of defense by blocking or removing microbes.
• Complement activation leads to opsonization, chemoattraction of leukocytes, inflammation and cytolysis by the membrane attack complex.
• Neutrophils are the most numerous leukocytes and fight bacteria, eosinophils target parasites, and basophils and mast cells release histamine in allergic reactions.
• Natural killer cells recognize and kill abnormal or infected cells by triggering apoptosis.
• Phagocytes bind pathogen-associated molecular patterns (PAMPs) with pattern recognition receptors such as Toll-like receptors.
• The five cardinal signs of inflammation are erythema, edema, heat, pain and altered function.
• Fever is a system-wide sign of inflammation that raises body temperature and stimulates the immune response.

Memory Tip: Picture a sprained ankle: red, swollen, hot, painful and hard to use. Those are the five cardinal signs of inflammation.

Common Mistake: Thinking that inflammation is always bad. Acute inflammation is protective; only chronic or excessive inflammation, with granulomas and scarring, becomes harmful.

Important Questions:

• What are the four protective outcomes of complement activation? Opsonization of pathogens, chemoattraction of leukocytes, induction of inflammation, and cytolysis through the membrane attack complex.
• What is the difference between exogenous and endogenous pyrogens? Exogenous pyrogens come from outside the body, such as the LPS endotoxin of gram-negative bacteria. Endogenous pyrogens are made by the body’s own leukocytes, such as interleukin-1, interleukin-6 and tumor necrosis factor, and they reset the hypothalamus to cause fever.

Chapter 18: Adaptive Specific Host Defenses

Difficulty: Hard · Key topics: antigens, antibodies, immunoglobulin classes, MHC, T cells, B cells, humoral and cellular immunity, primary and secondary responses, vaccines, herd immunity

Chapter 18 explains specific immunity, which has specificity and memory. It covers antigens and epitopes, the Y-shaped antibody with its Fab and Fc regions, the five antibody classes and their functions, MHC I and MHC II molecules and antigen-presenting cells, T cell maturation in the thymus, helper, cytotoxic and regulatory T cells, and B cell activation with primary and secondary responses. It ends with vaccines: the four kinds of acquired immunity, herd immunity, variolation and Jenner’s cowpox work, and live attenuated, inactivated, subunit, toxoid and conjugate vaccines.

Key Points:

• The first exposure to an antigen causes a primary response; later exposures cause a faster and stronger secondary response.
• Humoral immunity depends on antibodies made by B cells, and cellular immunity depends on T cells directed against intracellular pathogens.
• The five antibody classes are IgM, IgG, IgA, IgE and IgD, and antibodies neutralize, opsonize, agglutinate, activate complement and drive cell-mediated cytotoxicity.
• MHC I molecules are on all nucleated cells, and MHC II molecules are only on antigen-presenting cells: macrophages, dendritic cells and B cells.
• T cell receptor and B cell receptor diversity comes from genetic rearrangement of V, D and J gene segments.
• Activated helper T cells can become TH1, TH2, TH17 or memory cells, guided by the cytokines they meet.
• Vaccination gives artificial active immunity to individuals and builds herd immunity in populations.

Memory Tip: Use the rule of eight: CD4 times MHC II equals 8 and CD8 times MHC I equals 8. Helper T cells (CD4) meet MHC II, and cytotoxic T cells (CD8) meet MHC I.

Common Mistake: Assuming that every antigen needs T cell help to activate B cells. Protein antigens are T-dependent, but repetitive nonprotein epitopes can activate B cells without T cells, producing IgM and no memory cells.

Important Questions:

• What is the difference between humoral and cellular adaptive immunity? Humoral immunity works through antibodies produced by B cells. Cellular immunity works through T cells, which are directed against intracellular pathogens and infected cells.
• What are the pros and cons of inactivated and live attenuated vaccines? Both contain whole pathogens, which are killed or inactivated in one case and weakened in the other. Live attenuated vaccines need careful storage and can cause disease in immunocompromised patients or revert to full virulence. Inactivated vaccines cannot cause an active infection and store well, but they usually need higher doses and multiple boosters.

Chapter 19: Diseases of the Immune System

Difficulty: Medium · Key topics: hypersensitivity types I to IV, anaphylaxis, ABO and Rh incompatibility, autoimmune diseases, transplant rejection, immunodeficiency, cancer immunotherapy

Chapter 19 covers what happens when the immune system goes wrong. It explains the four types of hypersensitivity: type I (IgE and mast cells, hives, hay fever, anaphylaxis), type II (antibodies on cell surfaces, ABO and Rh incompatibility), type III (immune complexes) and type IV (T-cell mediated), with diagnosis and treatment. It then covers organ-specific and systemic autoimmune diseases, graft types and rejection with graft-versus-host disease, primary and secondary immunodeficiencies, and cancer immunobiology with immunotherapy.

Key Points:

• In type I hypersensitivity, IgE attaches to mast cells; on second exposure the allergen cross-links IgE and triggers degranulation.
• Type II involves antibodies binding to cell antigens, as in hemolytic transfusion reaction and hemolytic disease of the newborn.
• Type III is caused by immune complexes that build up in tissues and cause damaging inflammation.
• Type IV is mediated by helper T cells, macrophages, eosinophils and cytotoxic T cells, not by antibodies.
• Autoimmune diseases result from a breakdown in immunological tolerance; examples are celiac disease, type 1 diabetes, multiple sclerosis, rheumatoid arthritis and lupus.
• Grafts are classed as autografts, isografts, allografts or xenografts, and MHC (HLA) differences decide the risk of rejection.
• Primary immunodeficiencies are genetic, such as SCID, while secondary ones are acquired through disease, diet or environmental exposure.

Memory Tip: Use ACID for the hypersensitivities: Type I Allergic, Type II Cytotoxic, Type III Immune complex, Type IV Delayed.

Common Mistake: Thinking that type IV hypersensitivity involves antibodies. It is mediated by T cells, which is why the reaction is delayed.

Important Questions:

• Why is a parent usually a better match for a transplant than a random person? A child inherits half of its MHC (HLA) genes from each parent, so the tissues share more MHC molecules, and genetic differences in MHC genes are what drive rejection.
• How can tumor antigens be targeted without causing an anti-self response? Tumor antigens are self-molecules found only on abnormal cells, so an immune response aimed at them can attack the cancer cells without attacking normal cells.

Chapter 20: Laboratory Analysis of the Immune Response

Difficulty: Medium · Key topics: polyclonal and monoclonal antibodies, precipitation, agglutination, Coombs test, ELISA, Western blot, immunofluorescence, flow cytometry

Chapter 20 shows how antibodies are used as laboratory tools. It begins with polyclonal antisera and monoclonal antibodies made from hybridomas, and their clinical uses. It then covers precipitation tests (ring test, Ouchterlony, radial immunodiffusion), flocculation, neutralization assays, immunoelectrophoresis, Western blot and complement fixation, followed by agglutination assays, hemagglutination, Coombs’ tests and blood typing. The last sections cover enzyme immunoassays including immunostaining, ELISA and lateral flow tests, and fluorescent antibody techniques, flow cytometry and cell sorting.

Key Points:

• Polyclonal antisera contain antibodies to many epitopes, while monoclonal antibodies bind one epitope and are usually made from hybridomas.
• A precipitin lattice forms only when antigen and antibody are in the correct ratio.
• The VDRL test for syphilis is a flocculation test in which antibodies bind cardiolipin.
• In a Western blot, proteins are transferred to a nitrocellulose membrane and found with labeled antibodies.
• Direct ELISA quantifies an antigen, while indirect ELISA detects antibodies in patient serum.
• Lateral flow tests, such as pregnancy tests, use immunochromatography to show colored antigen-antibody complexes.
• Flow cytometry uses fluorescent monoclonal antibodies to count cell subsets, and cell sorters separate them.

Memory Tip: Direct tests look for the antigen using one labeled antibody. Indirect tests look for the patient’s antibody and use a second, labeled antibody, so indirect means two steps.

Common Mistake: Reading hemolysis in the complement fixation test as positive. Hemolysis means complement was free, so no antibody was present to use it up, which is a negative test.

Important Questions:

• Why are polyclonal antibodies more likely to show cross-reactivity than monoclonal antibodies? Polyclonal antisera are mixtures of antibodies that bind many different epitopes, so there is more chance that some bind similar epitopes on other antigens. A monoclonal antibody binds a single epitope with high specificity.
• Why would a doctor order a direct Coombs’ test for a baby born with jaundice? The test detects antibodies bound to the baby’s red blood cells; Coombs’ reagent cross-links them and causes hemagglutination, which points to antibody-mediated destruction of red cells.

Chapter 21: Skin and Eye Infections

Difficulty: Easy · Key topics: skin layers, normal microbiota, staphylococcal and streptococcal infections, MRSA, necrotizing fasciitis, conjunctivitis, herpes, tineas, Acanthamoeba, Loa loa

Chapter 21 is the first of six body-system chapters. It reviews the layers of the skin (epidermis, dermis, hypodermis), the normal skin microbiota and the anatomy of the eye. It covers bacterial infections such as staphylococcal and streptococcal diseases, MRSA, impetigo, cellulitis, necrotizing fasciitis, acne, anthrax, conjunctivitis, trachoma and keratitis. Later sections cover viral infections (warts, oral herpes, roseola, fifth disease, viral conjunctivitis, herpes keratitis), fungal skin infections (tineas, aspergillosis, candidiasis, sporotrichosis) and the parasites Acanthamoeba and Loa loa.

Key Points:

• The skin has two main layers, the epidermis and dermis, over the hypodermis, and it is an effective physical barrier against microbes.
• S. aureus causes folliculitis, furuncles, carbuncles and staphylococcal scalded skin syndrome, and MRSA strains resist many antibiotics.
• Group A streptococci (S. pyogenes) are often responsible for cellulitis and erysipelas and are one cause of necrotizing fasciitis.
• Tineas are caused by dermatophytes of the genera Trichophyton, Epidermophyton and Microsporum.
• Acanthamoeba keratitis often follows improper disinfection of contact lenses or swimming while wearing them.
• Loiasis, or eye worm, is caused by Loa loa and is transmitted by deerflies.

Memory Tip: For every body-system chapter, sort the diseases by agent type in the same order as the sections: bacteria, viruses, fungi, then parasites.

Common Mistake: Calling every fungal skin infection ringworm. Ringworm is tinea corporis, a tinea of the body; tineas elsewhere are named after the body part.

Important Questions:

• What is a good first test to tell a streptococcal infection from a staphylococcal one? The catalase test. Staphylococcus species are catalase-positive and Streptococcus species are catalase-negative.
• How are leukocidins linked to pus production? Leukocidins made by some S. aureus strains kill white blood cells, and the dead cells contribute to the formation of pus.

Chapter 22: Respiratory System Infections

Difficulty: Medium · Key topics: upper and lower respiratory tract, strep throat, diphtheria, pneumonia, tuberculosis, pertussis, common cold, influenza, SARS and MERS, measles, respiratory mycoses

Chapter 22 covers infections of the respiratory tract. It starts with the anatomy of the upper and lower tract, its defenses and normal microbiota. Bacterial diseases include strep throat and its sequelae, otitis media, diphtheria, the different pneumonias, tuberculosis, pertussis, Legionnaires disease and Q fever. Viral diseases include the common cold, influenza, viral pneumonia, SARS and MERS, measles, rubella, chickenpox and shingles. The last section covers respiratory fungal infections, including histoplasmosis, coccidioidomycosis, blastomycosis, mucormycosis, aspergillosis, Pneumocystis pneumonia and cryptococcosis.

Key Points:

• The respiratory tract is divided into upper and lower regions at the epiglottis; the upper tract has a diverse microbiota and the lower tract has very few microbes.
• Streptococcus pyogenes causes strep throat, which can lead to scarlet fever, acute rheumatic fever and acute glomerulonephritis.
• Diphtheria toxin kills cells in the pharynx and produces a pseudomembrane; the disease is rare because of vaccination.
• The common cold can be caused by more than 200 viruses, mainly rhinoviruses, coronaviruses and adenoviruses.
• Influenza changes through antigenic drift and shift, so new vaccines are developed every year.
• SARS and MERS are coronavirus infections that appear to come from animals; SARS has not been seen in humans since 2004.
• Fungal respiratory disease is rare in healthy people but can be severe in the immunocompromised, and amphotericin B controls most of these infections.

Memory Tip: Sort the diseases by where they strike. Upper tract: throat, ear, sinus. Lower tract: bronchi and lungs, where pneumonia and tuberculosis live.

Common Mistake: Expecting antibiotics to treat a cold or influenza. Both are viral, and antibiotics act only on bacteria.

Important Questions:

• Why is the lower respiratory tract essentially sterile? The mucociliary escalator and the other innate and adaptive defenses remove microbes from the lower tract, so few microbial inhabitants are found there, and those that are found may be transients.
• Since everyone has had many colds, why are we not resistant to future colds? Colds can be caused by more than 200 different viruses, so immunity to one virus does not protect against the others.

Chapter 23: Urogenital System Infections

Difficulty: Medium · Key topics: urinary and reproductive anatomy, cystitis, pyelonephritis, gonorrhea, chlamydia, syphilis, genital herpes, HPV, vaginal candidiasis, trichomoniasis

Chapter 23 covers infections of the urinary and reproductive systems. It reviews the anatomy of the urinary tract and the male and female reproductive systems, the normal microbiota, and the general signs and causes of urogenital infection. Bacterial diseases include cystitis, pyelonephritis, leptospirosis, nongonococcal urethritis, bacterial vaginosis, gonorrhea, chlamydia, syphilis and chancroid. The chapter then covers viral infections (genital herpes, neonatal herpes, human papillomaviruses), fungal infection by Candida, and the protozoan infection trichomoniasis.

Key Points:

• The bladder and urethra are the most common sites of urinary infection, and cystitis is commonly caused by fecal bacteria such as E. coli.
• Bacterial vaginosis is caused by an imbalance in the vaginal microbiota, with fewer lactobacilli and a higher vaginal pH.
• Chlamydia, caused by C. trachomatis, is the most commonly reported STI, and most infections have no symptoms.
• Syphilis, caused by T. pallidum, has primary, secondary and tertiary stages.
• Human papillomaviruses are the most common sexually transmitted viruses; some types cause genital warts and others cause cervical cancer.
• Trichomonas vaginalis is treated with the antiflagellate drugs tinidazole and metronidazole.

Memory Tip: Link each infection to its organism type: gonorrhea, chlamydia and syphilis to bacteria; herpes and HPV to viruses; vaginal candidiasis to a fungus; trichomoniasis to a protozoan.

Common Mistake: Assuming that no symptoms means no infection. Chlamydia and trichomoniasis are often asymptomatic, and HPV infection is often asymptomatic too.

Important Questions:

• Is it true that human papillomaviruses can always be detected by the presence of genital warts? No. Some HPV types cause genital warts, but HPV infection is often asymptomatic, and other types, which are not the wart types, are associated with cervical cancer.
• Name a bacterium, a fungus and a protozoan associated with vaginitis. Gardnerella vaginalis (bacterial vaginosis), Candida (vaginal candidiasis) and Trichomonas vaginalis (trichomoniasis).

Chapter 24: Digestive System Infections

Difficulty: Medium · Key topics: oral microbiota, dental caries, food poisoning, Salmonella, E. coli, cholera, H. pylori, C. difficile, hepatitis viruses, giardiasis, intestinal helminths

Chapter 24 covers infections of the mouth and gastrointestinal tract. It starts with the anatomy and normal microbiota of the digestive system and the general signs of oral and intestinal disease. It then covers diseases of the mouth, such as dental caries, periodontal disease, thrush and mumps, and bacterial gastrointestinal infections, including staphylococcal food poisoning, shigellosis, salmonellosis, typhoid, E. coli, cholera, peptic ulcers and C. difficile. Later sections cover viral gastroenteritis and hepatitis, protozoan infections such as giardiasis, and helminths such as Ascaris, hookworm, pinworms and tapeworms.

Key Points:

• Constant movement of material, a mucus layer, the normal microbiota and the harsh chemistry of the stomach help prevent colonization by pathogens.
• Dental caries are linked to Streptococcus mutans, which ferments sucrose to acids that dissolve enamel.
• E. coli strains ETEC, EPEC, EIEC and EHEC cause different illnesses of varying severity.
• Helicobacter pylori is associated with peptic ulcers, and Clostridioides difficile is a major hospital-acquired infection after antibiotic use.
• Rotaviruses, noroviruses and astroviruses are common viral causes of gastroenteritis.
• Five unrelated viruses, hepatitis A, B, C, D and E, cause hepatitis and differ in transmission, treatment and risk of chronic infection.
• Rehydration and supportive care are the usual treatment for most gastrointestinal infections.

Memory Tip: Follow the food. For each disease, note the source (water, undercooked meat, eggs, soil) because most prevention questions follow from the route of infection.

Common Mistake: Treating every food-related illness as a spreading infection. In staphylococcal food poisoning the toxin already in the food causes the illness, so symptoms begin soon after eating.

Important Questions:

• Why do sugary foods promote dental caries? When sucrose is broken down by bacteria in the mouth, the glucose is used to make dextran for the plaque biofilm and the fructose is fermented to lactic acid and other acids, which dissolve the minerals of the tooth enamel.
• Which forms of viral hepatitis are transmitted by the fecal-oral route? Hepatitis A and hepatitis E spread through contaminated food or water, while hepatitis B, C and D spread through blood and body fluids.

Chapter 25: Circulatory and Lymphatic System Infections

Difficulty: Hard · Key topics: circulatory and lymphatic anatomy, sepsis, toxic shock, plague, Lyme disease, rickettsial diseases, mononucleosis, dengue, Ebola, HIV, malaria, toxoplasmosis

Chapter 25 covers infections of the blood and lymph. It reviews the anatomy of the circulatory and lymphatic systems, which have no normal microbiota, and conditions such as sepsis, SIRS, endocarditis and lymphangitis. Bacterial diseases include toxic shock syndrome, gas gangrene, tularemia, brucellosis, plague, typhus, Rocky Mountain spotted fever, Lyme disease and relapsing fever. Viral diseases include mononucleosis, cytomegalovirus infection, yellow fever, dengue, chikungunya, Ebola, hantavirus and HIV. Parasitic diseases include malaria, toxoplasmosis, babesiosis, Chagas disease, leishmaniasis and schistosomiasis.

Key Points:

• The circulatory and lymphatic systems have no normal microbiota, so any microbe found there is abnormal.
• Pathogens or toxins in the bloodstream can provoke SIRS, sepsis and endocarditis, which can be fatal.
• Tularemia, brucellosis, cat-scratch disease and plague are zoonotic; Lyme disease, Rocky Mountain spotted fever and the typhus group are spread by arthropod vectors.
• Epstein-Barr virus is linked to infectious mononucleosis and Burkitt lymphoma, and cytomegalovirus can cause serious congenital infection.
• Yellow fever, dengue and chikungunya cause high fever and vascular damage, and treatment is limited to supportive care.
• HIV progresses through three stages to AIDS, and antiretroviral therapy combines several drugs to suppress the viral load.
• Malaria is caused by Plasmodium species transmitted by Anopheles mosquitoes, and the parasite infects and destroys red blood cells.

Memory Tip: Group the vector-borne diseases by vector: mosquito (malaria, dengue, yellow fever, chikungunya), tick (Lyme disease, Rocky Mountain spotted fever), flea (plague, murine typhus) and louse (epidemic typhus, trench fever).

Common Mistake: Treating vector-borne diseases like person-to-person infections. Most need an insect vector or an animal reservoir, so control targets the vector as well as the patient.

Important Questions:

• What is the main cause of the symptoms of Plasmodium falciparum infection? The parasite infects and destroys human red blood cells, which leads to anemia, organ damage and, in severe cases, blood vessel necrosis and death.
• Why should pregnant people avoid cleaning a cat’s litter box, or use gloves when they do? Domestic cats are the definitive host of Toxoplasma, and toxoplasmosis can cause serious infection in developing fetuses.

Chapter 26: Nervous System Infections

Difficulty: Medium · Key topics: central and peripheral nervous system, meninges, blood-brain barrier, meningitis, tetanus, botulism, leprosy, rabies, polio, prions, neuromycoses, Naegleria

Chapter 26 closes the body-system chapters with infections of the nervous system. It reviews the central and peripheral nervous systems, the three meninges, the cells of the nervous system and the blood-brain barrier, which keeps the CNS free of normal microbiota. Bacterial diseases include meningitis, tetanus, botulism, listeriosis and leprosy. The next section covers viral meningitis, arboviral encephalitis, Zika, rabies, polio and prion diseases. The last section covers cryptococcal meningitis, amoebic meningitis and encephalitis, African trypanosomiasis, neurotoxoplasmosis and neurocysticercosis.

Key Points:

• The brain is protected by the skull, the three meninges (dura mater, arachnoid mater and pia mater) and the blood-brain barrier.
• There is no normal microbiota in the central nervous system, and inflammation of the meninges is meningitis while inflammation of the brain is encephalitis.
• Bacterial meningitis can be caused by H. influenzae, N. meningitidis, S. pneumoniae and group B streptococci, and is diagnosed from the cerebrospinal fluid.
• Clostridium neurotoxins cause tetanus and botulism by interfering with neurotransmitter release.
• Viral meningitis is more common and generally less severe than bacterial meningitis.
• Rabies is nearly always fatal when untreated, and prion diseases such as Creutzfeldt-Jakob disease and kuru are untreatable.
• Zika infection in pregnancy can cause the birth defect microcephaly.

Memory Tip: The suffix -itis means inflammation. Meningitis is inflammation of the meninges and encephalitis is inflammation of the brain itself, so the first part of the word tells you where the infection sits.

Common Mistake: Assuming that all meningitis is equally dangerous. Viral meningitis is common and usually milder, while bacterial meningitis is a medical emergency.

Important Questions:

• How is the blood-brain barrier formed? Capillaries in the brain are less permeable than elsewhere because their endothelial cells form tight junctions, so materials in the blood can interact with the CNS only to a very limited extent. It keeps most microbes and many drugs out.
• How could a person contract variant Creutzfeldt-Jakob disease from a cow with BSE? By eating products from the infected animal. BSE and variant CJD are caused by prions, which survive cooking and cannot be treated.

Appendices A–D and the Glossary

Appendix · Difficulty: Easy · Key topics: atomic structure, chemical bonds, acids and bases, scientific notation, logarithms, generation time, most probable number, metabolic pathway diagrams, taxonomy tables, glossary

The back matter holds four appendices and a glossary. Appendix A reviews the physics and chemistry that matter for microbiology: atomic structure, elements, covalent and ionic bonds, molecular mass and the mole, energy, chemical reactions, water and solutions, and acids and bases. Appendix B covers the mathematics: powers, percentages, scientific notation, logarithms and rounding, with worked examples of generation time and most probable number. Appendix C lays out the metabolic pathways, including the Entner-Doudoroff and pentose-phosphate pathways, the TCA cycle, beta oxidation and the Calvin-Benson cycle. Appendix D tabulates the clinically relevant bacteria, viruses, fungi, protozoa and helminths, and Appendix E is the glossary.

Key Points:

• Appendix A covers acids and bases, which you need before the pH sections of Chapter 9.
• Appendix B gives the equation for cell numbers during growth by binary fission: Ni = N0 x 2^j, where j is the number of generations.
• A worked example in Appendix B: starting with 4 cells and a 30-minute generation time, there are 32 cells after 90 minutes.
• Appendix C collects the pathways that Chapter 8 describes in words, including the pentose-phosphate pathway and beta oxidation.
• Appendix D groups the clinically relevant pathogens as bacterial, viral, fungal, protozoan and parasitic helminth pathogens.

Memory Tip: Work through the generation time example in Appendix B with a calculator before you read Chapter 9. Once you have computed 4 x 2^3 yourself, the growth curve numbers make sense.

Common Mistake: Skipping Appendix A and then struggling with Chapters 7 and 8. Bonds, acids and bases and energy are used constantly in the biochemistry and metabolism chapters.

Important Questions:

• What equation estimates the number of bacterial cells after several generations? Ni = N0 x 2^j, where N0 is the starting number of cells and j is the number of times the population doubles. With 4 cells and 3 generations the result is 4 x 8 = 32 cells.
• How does Appendix B say to round a number when the retained digit is followed by 5? Round up if the retained digit is odd and round down if it is even, so that the retained digit is always even after rounding.

Download Microbiology PDF (Free)

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How to Study This Book

Microbiology has 26 chapters, four appendices and a glossary. The book does not divide itself into parts, and this page gives one block per chapter plus one for the appendices. According to its preface, the order runs from fundamentals to applications: Chapters 1 to 6 are an overview of the field, microscopy, the cell and each group of microorganisms; Chapters 7 to 14 cover biochemistry, metabolism, growth, genetics and the control of microbes; from Chapter 15 the focus turns to pathogenicity and the immune system; and the last six chapters survey infectious disease body system by body system. The book was written for a single-semester course, but a BS Biology course can spread it over a full semester or two.

Start with Chapter 1 and read Chapters 2 and 3 properly, because later chapters assume them. The Gram stain, acid-fast stain and microscope types from Chapter 2 return in the bacterial chapters, and the cell wall, ribosome and membrane details of Chapter 3 return in Chapter 14 (how drugs target bacteria) and Chapter 17 (how the body recognizes bacteria). Chapters 4 and 5 are a catalogue of organisms, so study them with a table: group, key feature, one example, one disease. Chapter 6 is best read together with Chapter 11, because transduction and the lysogenic cycle appear in both.

Chapters 7, 8 and 9 form a chain. Read the biochemistry in Chapter 7 first, then the metabolism in Chapter 8, because glycolysis, the Krebs cycle and the electron transport system are explained in terms of the carbohydrates, lipids and proteins of Chapter 7. Chapter 9 uses both: the oxygen, pH and temperature sections depend on the enzymes and electron transport of Chapter 8. If your chemistry is weak, read Appendix A first, and try the generation time example in Appendix B before the growth curve in Chapter 9.

The genetics chapters also build on each other: Chapter 10 (what DNA and RNA are), then Chapter 11 (how they are copied, read and changed), then Chapter 12 (how scientists use them). Chapter 11 is the hardest in the book, with replication, transcription, translation, mutations, gene transfer and operons in one chapter, so take it one section at a time. Chapter 12 is a methods chapter; if your course is not molecular, learn PCR, gel electrophoresis, blotting and cloning at the level of the Key Points above and skim the rest.

Chapters 13 and 14 are the practical heart of the book for health students. Chapter 13 gives the vocabulary of sterilization, disinfection and antisepsis, and Chapter 14 depends on Chapters 3, 10 and 11 to explain why each drug class works and why resistance spreads. Chapters 15 and 16 give the language of infectious disease and epidemiology that every later chapter uses, so read them before Chapters 21 to 26. Read the immunity block in order: Chapter 17 (innate), Chapter 18 (adaptive), Chapter 19 (when immunity causes disease) and Chapter 20 (laboratory tests that use antibodies). Chapter 20 is shorter on new theory and rewards a diagram of each test.

In Chapters 21 to 26 each chapter opens with the anatomy and normal microbiota of its body system, then moves through bacterial, viral, fungal and parasitic infections. Do not try to memorize them all at once. Make one revision table per chapter with causative agent, source or vector, main symptom and treatment; the Disease Profile boxes in these chapters give you exactly those headings. Most chapters also carry a multi-part Clinical Focus case study, Micro Connections and Eye on Ethics boxes, and some include a Case in Point, which are good practice for applying the content to a patient.

The book has 1,166 review questions: 444 multiple choice, 279 fill in the blank, 226 short answer, 159 critical thinking, 43 true/false and 15 matching. There are also Check Your Understanding questions inside each section, which have no published answers. According to the preface, answers to the multiple choice, true/false, fill in the blank and matching questions are in the book’s Answer Key, while answers to short answer and critical thinking questions are not provided to students, so try those yourself and check them against the chapter text.

This is a textbook, not a laboratory manual. It explains how techniques such as staining, culturing and ELISA work, but it does not give lab procedures or safety protocols, and it has no practical exercises. Its disease data and public health examples are largely drawn from the United States, and it was written for non-majors and allied health students rather than for specialist bacteriologists. For a research-level view of one group of organisms you will need a more specialized text later.

Used In These Programs

This book is used for the Microbiology course in BS Biology and in health-related degree programs. Browse all Microbiology books or all Biology books.

Who Should Read This

Microbiology by Parker, Schneegurt and colleagues is written for a first- or second-year university student taking a general microbiology course, which in Pakistan usually means a BS Biology or microbiology student, or a student in nursing, pharmacy, laboratory technology or another allied health program. It is the OpenStax book for non-majors with an allied health focus, so it explains terms from first principles and ties each topic to patients and real cases, but it assumes school-level biology and chemistry. Students who need a refresher on cells, enzymes, bacteria and viruses can start with the Biology 1st Year FSc book, and the genetics and immunity chapters connect to the Biology 2nd Year FSc book. It is not a laboratory manual and not a specialist text, so research-level work on one group of organisms will need further reading.

Applicable Universities

This book is useful for students at Pakistani universities offering BS Biology, microbiology and allied health programs with a microbiology course, including University of the Punjab, University of Karachi, Quaid-i-Azam University, COMSATS University Islamabad, Dow University of Health Sciences, University of Health Sciences Lahore, Riphah International University, and other HEC-recognized institutions.

FAQs

Related Books

• Biology 1st Year Book – Punjab Board FSC (school-level groundwork on cells, enzymes, respiration, bacteria and viruses)
• Biology 2nd Year Book – Punjab Board FSC (immunity, genetics and biotechnology topics that return in Chapters 10 to 12 and 17 to 20)
• Biology Class 10 English Medium – Punjab Board PCTB (a school-level start on genetics and biotechnology before the genetics chapters)
• Chemistry 1st Year Book – Punjab Board FSC (the bonding and solutions chemistry behind Chapter 7 and Appendix A)

Microbiology gives BS Biology and health science students a complete, free guide from microscopes and cells to infection and immunity. Browse more Biology books or the whole University Books section.

Microbiology, by Nina Parker, Mark Schneegurt, Anh-Hue Thi Tu, Brian M. Forster, Philip Lister and contributing authors. OpenStax, Rice University. Free under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International licence (CC BY-NC-SA 4.0). Access for free at https://openstax.org/details/books/microbiology