,CONTENT Chapter 19: Rickettsia, Ehrlichia,
Anaplasma, and Coxiella
Chapter 1: Introduction to
Microbiology Chapter 20: Fungi
Chapter 2: Normal Flora Chapter 21: Protozoa
Chapter 3: Pathogenicity of Chapter 22: Helminths
Microorganisms
Chapter 23: Introduction to the
Chapter 4: Diagnostic Microbiology Viruses
Chapter 5: Vaccines and Chapter 24: Nonenveloped DNA
Antimicrobial Agents Viruses
Chapter 6: Bacterial Structure, Chapter 25: Enveloped DNA Viruses
Growth, and Metabolism
Chapter 26: Hepatitis B and Hepatitis
Chapter 7: Bacterial Genetics D (Delta) Viruses
Chapter 8: Staphylococci Chapter 27: Positive-Strand RNA
Viruses
Chapter 9: Streptococci
Chapter 28: Retroviruses
Chapter 10: Gram-Positive Rods
Chapter 29: Negative-Strand RNA
Chapter 11: Neisseriae Viruses
Chapter 12: Gastrointestinal Gram- Chapter 30: Double-Stranded RNA
Negative Rods Viruses: Reoviridae
Chapter 13: Other Gram-Negative Chapter 31: Unconventional
Rods Infectious Agents
Chapter 14: Clostridia and Other Chapter 32: Quick Review of
Anaerobic Rods Clinically Important Microorganisms
Chapter 15: Spirochetes Chapter 33: Disease Summaries
Chapter 16: Mycoplasma Chapter 34: Illustrated Case
Studies
Chapter 17: Chlamydiae
Chapter 18: Mycobacteria and
Actinomycetes
,Ch. 1: Introduction to Microbiology. Each question has four options (A–D), the
answer shown only as Answer: X, a deep rationale, and key words.
1. Which approach most reliably reconstructs evolutionary relationships among
prokaryotes?
A. Gram stain and cell morphology
B. 16S rRNA gene sequencing and phylogenetic analysis
C. Biochemical metabolic profiling
D. Colony morphology on selective media
Answer: B
Rationale: The 16S rRNA gene contains conserved regions for universal
primer binding and variable regions that reflect evolutionary divergence;
phylogenetic trees derived from 16S sequences give a molecular-based
taxonomy that is robust across broad phyletic lines. Phenotypic methods
(Gram stain, metabolism, colony appearance) are useful for identification
and clinical workup but are influenced by convergent evolution, horizontal
gene transfer, and environmental expression of traits. Modern microbial
systematics therefore uses ribosomal RNA sequences (often supplemented
by whole-genome analyses) to infer deep evolutionary relationships. Caveat:
horizontal gene transfer can blur some gene histories, which is why multi-
locus and genome-wide approaches are sometimes required.
Key words: 16S rRNA, molecular phylogeny, conserved/variable regions,
molecular taxonomy
2. The phenomenon of “colonization resistance” provided by the normal
microbiota most directly involves which mechanism?
A. Microbiota-mediated production of bacteriophages that lyse incoming
pathogens
B. Competition for nutrients and niche plus production of antimicrobial
metabolites (e.g., bacteriocins, short-chain fatty acids)
C. Constitutive secretion of pathogen-specific IgG by commensals
D. Structural modification of host receptors to prevent pathogen binding
Answer: B
Rationale: Colonization resistance refers to the ability of resident microbes
to prevent pathogen establishment by occupying adhesion sites, consuming
available nutrients, producing inhibitory compounds (bacteriocins, SCFAs,
acids), and modulating local pH and oxygen tension. While phage-mediated
interactions and host immune factors can contribute, the principal direct
protective effects are competition and metabolite-mediated suppression.
, These mechanisms reduce pathogen load and also prime innate immunity
(e.g., stimulating mucosal barriers). Disruption (antibiotics, diet) weakens
colonization resistance and predisposes to infection.
Key words: colonization resistance, bacteriocins, SCFAs, niche competition
3. Which limitation makes Koch’s original postulates inadequate for proving
causation for many modern infectious diseases?
A. They only apply to prokaryotic organisms
B. They assume the pathogen can be cultured and isolated in pure culture
and that disease is reproduced in a susceptible host, which fails for
unculturable organisms, polymicrobial diseases and asymptomatic carriers
C. They require molecular sequencing data to be valid
D. They are limited to zoonotic infections only
Answer: B
Rationale: Koch’s postulates were formulated when culturing and isolation
were the primary tools; they break down when pathogens cannot be cultured
(many viruses, obligate intracellular bacteria, some microbiome-associated
agents), when disease results from polymicrobial interactions, or when
carriers transmit without showing disease. Modern molecular Koch’s
postulates and epidemiologic/molecular evidence (PCR, metagenomics,
serology, animal models) extend causation criteria to such cases. Thus
reliance solely on classical postulates would lead to false negatives for many
pathogens.
Key words: Koch’s postulates, unculturable organisms, polymicrobial
disease, molecular Koch’s postulates
4. Which horizontal gene transfer mechanism is the principal driver for rapid
plasmid-mediated spread of multidrug resistance across diverse bacterial
species in clinical settings?
A. Transformation (uptake of naked DNA)
B. Conjugation (direct cell-to-cell transfer via conjugative plasmids/pili)
C. Generalized transduction by virulent phages
D. Vertical inheritance during binary fission only
Answer: B
Rationale: Conjugation enables direct transfer of conjugative plasmids
(often carrying multiple resistance determinants and mobilization elements)
between bacteria — including across species and genera — via sex pili or
type IV secretion systems. Transformation requires availability of naked
DNA and competence; generalized transduction is typically limited by phage
host range and less efficient for broad plasmid dissemination. Conjugative
plasmids often carry transfer genes, insertion sequences, and transposons
that facilitate rapid dissemination in hospital and agricultural environments.
, Key words: conjugation, plasmid transfer, pili, horizontal gene transfer,
MDR
5. Which statement best distinguishes endotoxin (LPS) from typical bacterial
exotoxins?
A. Endotoxins are secreted protein toxins that are heat-labile and highly
antigenic
B. Endotoxins are lipopolysaccharide components of Gram-negative outer
membranes; they are heat-stable, pyrogenic, and trigger TLR4-mediated
cytokine release
C. Exotoxins are lipopolysaccharides embedded in membranes and are
minimally antigenic
D. Exotoxins are polysaccharides that cause fever by acting on the
hypothalamus
Answer: B
Rationale: Endotoxin refers to LPS in the outer membrane of Gram-
negative bacteria; the lipid A moiety elicits strong innate immune responses
via TLR4, leading to TNF-α/IL-1 production and fever, and is relatively
heat-stable. Exotoxins, by contrast, are discrete secreted proteins (often
enzymatic), typically heat-labile and highly antigenic, with specific
molecular targets (e.g., ADP-ribosylation). Understanding this distinction
informs pathogenesis (septic shock from endotoxin versus targeted cellular
injury from exotoxins) and clinical management.
Key words: endotoxin, LPS, lipid A, TLR4, exotoxin
6. A “pathogenicity island” is best described as:
A. A self-replicating plasmid carrying metabolic genes only
B. A chromosomal region acquired by horizontal gene transfer that contains
clusters of virulence genes and often has atypical GC content and mobility
elements
C. A bacteriophage genome encoding only lytic enzymes
D. A transposon that encodes housekeeping metabolic pathways
Answer: B
Rationale: Pathogenicity islands are discrete genomic regions integrated in
the chromosome that encode virulence determinants (toxins, secretion
systems, adhesins); they frequently show GC content and codon bias
different from the host genome and are adjacent to tRNA genes or flanked
by insertion sequences indicative of horizontal acquisition. They can be
mobilizable by phage or plasmid events and explain rapid emergence of
pathogenic clones. Recognizing these islands helps link genotype to
phenotype and track virulence evolution.
, Key words: pathogenicity island, horizontal gene transfer, GC content,
virulence clusters
7. Why are bacteria in biofilms often tolerant (not genetically resistant) to
antibiotics used in clinical therapy?
A. Biofilm bacteria constitutively produce β-lactamases that inactivate all
antibiotics
B. Biofilm lifestyle increases mutation rates so resistance emerges quickly
C. Biofilm matrix limits antibiotic diffusion and creates metabolic gradients
that induce slow-growth/persister states and stress responses that reduce
antibiotic efficacy
D. Biofilms convert all cells into spores that are inherently resistant
Answer: C
Rationale: The extracellular polymeric substance (EPS) matrix impedes
penetration, and microenvironments within biofilms produce nutrient and
oxygen gradients causing many cells to be metabolically inactive or in a
persister state. Most antibiotics target active processes (cell wall synthesis,
translation), so slow-growing cells are less susceptible. Additionally, stress
responses and local enzyme concentration can contribute, but tolerance
(phenotypic) differs from heritable genetic resistance and is reversible when
cells disperse.
Key words: biofilm, EPS, persister cells, diffusion barrier, antibiotic
tolerance
8. For rapid and sensitive identification of an RNA virus directly from patient
specimens, which diagnostic method is preferred?
A. Viral culture in cell lines with cytopathic effect readout
B. Serology for IgM antibodies
C. Reverse transcription-quantitative PCR (RT-qPCR) targeting viral RNA
D. Transmission electron microscopy of concentrated specimens
Answer: C
Rationale: RT-qPCR converts viral RNA to cDNA and amplifies specific
targets rapidly with high sensitivity and specificity, enabling early detection
during acute infection. Viral culture is time-consuming and may fail for
fastidious viruses; serology (IgM) reflects host response and may be delayed
or cross-reactive; electron microscopy lacks sensitivity and is non-specific.
Molecular assays also permit quantitation and genotyping where needed.
Key words: RT-qPCR, RNA virus detection, molecular diagnostics,
sensitivity
9. The acid-fast (Ziehl-Neelsen) stain is essential for detecting which group of
organisms and why?
A. Gram-positive cocci because they retain crystal violet
, B. Mycobacteria because their mycolic acid–rich cell envelope is resistant to
decolorization with acid-alcohol
C. Encapsulated yeasts because their capsule excludes decolorizer
D. Spore-forming bacilli because spores take up carbol fuchsin
Answer: B
Rationale: Mycobacteria possess a waxy, mycolic acid-rich cell envelope
that resists conventional Gram staining and resist acid-alcohol
decolorization; the Ziehl-Neelsen procedure uses carbol fuchsin with heat,
followed by acid decolorization and methylene blue counterstain, enabling
visualization of acid-fast bacilli. This property is central to diagnosing
tuberculosis and related mycobacterial infections. Other organisms do not
exhibit true acid-fastness.
Key words: acid-fast stain, mycolic acids, Ziehl-Neelsen, mycobacteria
10.Which antimicrobial class primarily binds the 30S ribosomal subunit and
blocks tRNA entry, thereby inhibiting protein synthesis?
A. Chloramphenicol
B. Tetracyclines
C. Vancomycin
D. Rifampin
Answer: B
Rationale: Tetracyclines bind the 30S ribosomal subunit and prevent
aminoacyl-tRNA from entering the A site, producing a bacteriostatic effect.
Chloramphenicol acts on the 50S (peptidyl transferase), vancomycin inhibits
cell-wall peptidoglycan crosslinking, and rifampin inhibits DNA-dependent
RNA polymerase. Understanding ribosomal subunit targets underpins
mechanism-based antibiotic selection and resistance interpretation.
Key words: tetracycline, 30S subunit, protein synthesis inhibition,
bacteriostatic
11.Specialized transduction differs from generalized transduction because:
A. Specialized transduction randomly packages host DNA during the lytic
cycle
B. Specialized transduction involves a temperate (lysogenic) phage that
excises imprecisely and carries only adjacent host genes to new hosts
C. It occurs only during bacterial conjugation
D. It relies on uptake of free DNA from the environment
Answer: B
Rationale: Specialized transduction is mediated by lysogenic phages that
integrate at specific sites; upon induction, imprecise excision can capture
specific host genes adjacent to the prophage and package them into phage
particles, transferring those specific genes to recipient cells. Generalized
, transduction (by lytic phages) can package random pieces of host DNA. The
mechanism has evolutionary significance for gene transfer, including
virulence factors.
Key words: specialized transduction, lysogeny, prophage excision, gene
transfer
12.To culture obligate anaerobic bacteria from a clinical specimen reliably,
which laboratory condition is required?
A. Incubation in ambient air at 37°C
B. Incubation in 5% CO₂ atmosphere only
C. Strict oxygen-free conditions (anaerobic jar/chamber with reducing
agents or palladium catalyst) to maintain low redox potential
D. Microaerophilic environment with reduced O₂ but not zero O₂
Answer: C
Rationale: Obligate anaerobes are intolerant of molecular oxygen and
require oxygen-free conditions for growth; anaerobic chambers or jars with
gas packs or palladium catalysts and reducing media create these conditions.
Microaerophilic setups still have low levels of O₂ and are unsuitable for
strict anaerobes. Proper specimen transport and rapid processing are also
critical because oxygen exposure rapidly kills anaerobes.
Key words: obligate anaerobe, anaerobic chamber, reducing agents, redox
potential
13.Which domain of life is characterized by ether-linked membrane lipids,
unique RNA polymerases, and lack of peptidoglycan in most cell envelopes?
A. Bacteria
B. Archaea
C. Eukarya
D. Viruses
Answer: B
Rationale: Archaea possess distinctive membrane lipids with ether bonds to
isoprenoid chains (rather than bacterial/eukaryotic ester-linked fatty acids),
have RNA polymerases and ribosomal proteins resembling eukaryotes in
some respects, and their cell envelopes typically lack canonical
peptidoglycan (some have pseudopeptidoglycan or S-layers). These
molecular differences justify their classification as a separate domain and
explain physiological adaptations to extreme environments.
Key words: Archaea, ether lipids, pseudopeptidoglycan, domain distinctions
14.In Gram-negative bacteria, quorum sensing most commonly uses which
class of molecules as intercellular signals to coordinate group behaviors like
virulence and biofilm formation?
A. Short peptides similar to cytokines
Anaplasma, and Coxiella
Chapter 1: Introduction to
Microbiology Chapter 20: Fungi
Chapter 2: Normal Flora Chapter 21: Protozoa
Chapter 3: Pathogenicity of Chapter 22: Helminths
Microorganisms
Chapter 23: Introduction to the
Chapter 4: Diagnostic Microbiology Viruses
Chapter 5: Vaccines and Chapter 24: Nonenveloped DNA
Antimicrobial Agents Viruses
Chapter 6: Bacterial Structure, Chapter 25: Enveloped DNA Viruses
Growth, and Metabolism
Chapter 26: Hepatitis B and Hepatitis
Chapter 7: Bacterial Genetics D (Delta) Viruses
Chapter 8: Staphylococci Chapter 27: Positive-Strand RNA
Viruses
Chapter 9: Streptococci
Chapter 28: Retroviruses
Chapter 10: Gram-Positive Rods
Chapter 29: Negative-Strand RNA
Chapter 11: Neisseriae Viruses
Chapter 12: Gastrointestinal Gram- Chapter 30: Double-Stranded RNA
Negative Rods Viruses: Reoviridae
Chapter 13: Other Gram-Negative Chapter 31: Unconventional
Rods Infectious Agents
Chapter 14: Clostridia and Other Chapter 32: Quick Review of
Anaerobic Rods Clinically Important Microorganisms
Chapter 15: Spirochetes Chapter 33: Disease Summaries
Chapter 16: Mycoplasma Chapter 34: Illustrated Case
Studies
Chapter 17: Chlamydiae
Chapter 18: Mycobacteria and
Actinomycetes
,Ch. 1: Introduction to Microbiology. Each question has four options (A–D), the
answer shown only as Answer: X, a deep rationale, and key words.
1. Which approach most reliably reconstructs evolutionary relationships among
prokaryotes?
A. Gram stain and cell morphology
B. 16S rRNA gene sequencing and phylogenetic analysis
C. Biochemical metabolic profiling
D. Colony morphology on selective media
Answer: B
Rationale: The 16S rRNA gene contains conserved regions for universal
primer binding and variable regions that reflect evolutionary divergence;
phylogenetic trees derived from 16S sequences give a molecular-based
taxonomy that is robust across broad phyletic lines. Phenotypic methods
(Gram stain, metabolism, colony appearance) are useful for identification
and clinical workup but are influenced by convergent evolution, horizontal
gene transfer, and environmental expression of traits. Modern microbial
systematics therefore uses ribosomal RNA sequences (often supplemented
by whole-genome analyses) to infer deep evolutionary relationships. Caveat:
horizontal gene transfer can blur some gene histories, which is why multi-
locus and genome-wide approaches are sometimes required.
Key words: 16S rRNA, molecular phylogeny, conserved/variable regions,
molecular taxonomy
2. The phenomenon of “colonization resistance” provided by the normal
microbiota most directly involves which mechanism?
A. Microbiota-mediated production of bacteriophages that lyse incoming
pathogens
B. Competition for nutrients and niche plus production of antimicrobial
metabolites (e.g., bacteriocins, short-chain fatty acids)
C. Constitutive secretion of pathogen-specific IgG by commensals
D. Structural modification of host receptors to prevent pathogen binding
Answer: B
Rationale: Colonization resistance refers to the ability of resident microbes
to prevent pathogen establishment by occupying adhesion sites, consuming
available nutrients, producing inhibitory compounds (bacteriocins, SCFAs,
acids), and modulating local pH and oxygen tension. While phage-mediated
interactions and host immune factors can contribute, the principal direct
protective effects are competition and metabolite-mediated suppression.
, These mechanisms reduce pathogen load and also prime innate immunity
(e.g., stimulating mucosal barriers). Disruption (antibiotics, diet) weakens
colonization resistance and predisposes to infection.
Key words: colonization resistance, bacteriocins, SCFAs, niche competition
3. Which limitation makes Koch’s original postulates inadequate for proving
causation for many modern infectious diseases?
A. They only apply to prokaryotic organisms
B. They assume the pathogen can be cultured and isolated in pure culture
and that disease is reproduced in a susceptible host, which fails for
unculturable organisms, polymicrobial diseases and asymptomatic carriers
C. They require molecular sequencing data to be valid
D. They are limited to zoonotic infections only
Answer: B
Rationale: Koch’s postulates were formulated when culturing and isolation
were the primary tools; they break down when pathogens cannot be cultured
(many viruses, obligate intracellular bacteria, some microbiome-associated
agents), when disease results from polymicrobial interactions, or when
carriers transmit without showing disease. Modern molecular Koch’s
postulates and epidemiologic/molecular evidence (PCR, metagenomics,
serology, animal models) extend causation criteria to such cases. Thus
reliance solely on classical postulates would lead to false negatives for many
pathogens.
Key words: Koch’s postulates, unculturable organisms, polymicrobial
disease, molecular Koch’s postulates
4. Which horizontal gene transfer mechanism is the principal driver for rapid
plasmid-mediated spread of multidrug resistance across diverse bacterial
species in clinical settings?
A. Transformation (uptake of naked DNA)
B. Conjugation (direct cell-to-cell transfer via conjugative plasmids/pili)
C. Generalized transduction by virulent phages
D. Vertical inheritance during binary fission only
Answer: B
Rationale: Conjugation enables direct transfer of conjugative plasmids
(often carrying multiple resistance determinants and mobilization elements)
between bacteria — including across species and genera — via sex pili or
type IV secretion systems. Transformation requires availability of naked
DNA and competence; generalized transduction is typically limited by phage
host range and less efficient for broad plasmid dissemination. Conjugative
plasmids often carry transfer genes, insertion sequences, and transposons
that facilitate rapid dissemination in hospital and agricultural environments.
, Key words: conjugation, plasmid transfer, pili, horizontal gene transfer,
MDR
5. Which statement best distinguishes endotoxin (LPS) from typical bacterial
exotoxins?
A. Endotoxins are secreted protein toxins that are heat-labile and highly
antigenic
B. Endotoxins are lipopolysaccharide components of Gram-negative outer
membranes; they are heat-stable, pyrogenic, and trigger TLR4-mediated
cytokine release
C. Exotoxins are lipopolysaccharides embedded in membranes and are
minimally antigenic
D. Exotoxins are polysaccharides that cause fever by acting on the
hypothalamus
Answer: B
Rationale: Endotoxin refers to LPS in the outer membrane of Gram-
negative bacteria; the lipid A moiety elicits strong innate immune responses
via TLR4, leading to TNF-α/IL-1 production and fever, and is relatively
heat-stable. Exotoxins, by contrast, are discrete secreted proteins (often
enzymatic), typically heat-labile and highly antigenic, with specific
molecular targets (e.g., ADP-ribosylation). Understanding this distinction
informs pathogenesis (septic shock from endotoxin versus targeted cellular
injury from exotoxins) and clinical management.
Key words: endotoxin, LPS, lipid A, TLR4, exotoxin
6. A “pathogenicity island” is best described as:
A. A self-replicating plasmid carrying metabolic genes only
B. A chromosomal region acquired by horizontal gene transfer that contains
clusters of virulence genes and often has atypical GC content and mobility
elements
C. A bacteriophage genome encoding only lytic enzymes
D. A transposon that encodes housekeeping metabolic pathways
Answer: B
Rationale: Pathogenicity islands are discrete genomic regions integrated in
the chromosome that encode virulence determinants (toxins, secretion
systems, adhesins); they frequently show GC content and codon bias
different from the host genome and are adjacent to tRNA genes or flanked
by insertion sequences indicative of horizontal acquisition. They can be
mobilizable by phage or plasmid events and explain rapid emergence of
pathogenic clones. Recognizing these islands helps link genotype to
phenotype and track virulence evolution.
, Key words: pathogenicity island, horizontal gene transfer, GC content,
virulence clusters
7. Why are bacteria in biofilms often tolerant (not genetically resistant) to
antibiotics used in clinical therapy?
A. Biofilm bacteria constitutively produce β-lactamases that inactivate all
antibiotics
B. Biofilm lifestyle increases mutation rates so resistance emerges quickly
C. Biofilm matrix limits antibiotic diffusion and creates metabolic gradients
that induce slow-growth/persister states and stress responses that reduce
antibiotic efficacy
D. Biofilms convert all cells into spores that are inherently resistant
Answer: C
Rationale: The extracellular polymeric substance (EPS) matrix impedes
penetration, and microenvironments within biofilms produce nutrient and
oxygen gradients causing many cells to be metabolically inactive or in a
persister state. Most antibiotics target active processes (cell wall synthesis,
translation), so slow-growing cells are less susceptible. Additionally, stress
responses and local enzyme concentration can contribute, but tolerance
(phenotypic) differs from heritable genetic resistance and is reversible when
cells disperse.
Key words: biofilm, EPS, persister cells, diffusion barrier, antibiotic
tolerance
8. For rapid and sensitive identification of an RNA virus directly from patient
specimens, which diagnostic method is preferred?
A. Viral culture in cell lines with cytopathic effect readout
B. Serology for IgM antibodies
C. Reverse transcription-quantitative PCR (RT-qPCR) targeting viral RNA
D. Transmission electron microscopy of concentrated specimens
Answer: C
Rationale: RT-qPCR converts viral RNA to cDNA and amplifies specific
targets rapidly with high sensitivity and specificity, enabling early detection
during acute infection. Viral culture is time-consuming and may fail for
fastidious viruses; serology (IgM) reflects host response and may be delayed
or cross-reactive; electron microscopy lacks sensitivity and is non-specific.
Molecular assays also permit quantitation and genotyping where needed.
Key words: RT-qPCR, RNA virus detection, molecular diagnostics,
sensitivity
9. The acid-fast (Ziehl-Neelsen) stain is essential for detecting which group of
organisms and why?
A. Gram-positive cocci because they retain crystal violet
, B. Mycobacteria because their mycolic acid–rich cell envelope is resistant to
decolorization with acid-alcohol
C. Encapsulated yeasts because their capsule excludes decolorizer
D. Spore-forming bacilli because spores take up carbol fuchsin
Answer: B
Rationale: Mycobacteria possess a waxy, mycolic acid-rich cell envelope
that resists conventional Gram staining and resist acid-alcohol
decolorization; the Ziehl-Neelsen procedure uses carbol fuchsin with heat,
followed by acid decolorization and methylene blue counterstain, enabling
visualization of acid-fast bacilli. This property is central to diagnosing
tuberculosis and related mycobacterial infections. Other organisms do not
exhibit true acid-fastness.
Key words: acid-fast stain, mycolic acids, Ziehl-Neelsen, mycobacteria
10.Which antimicrobial class primarily binds the 30S ribosomal subunit and
blocks tRNA entry, thereby inhibiting protein synthesis?
A. Chloramphenicol
B. Tetracyclines
C. Vancomycin
D. Rifampin
Answer: B
Rationale: Tetracyclines bind the 30S ribosomal subunit and prevent
aminoacyl-tRNA from entering the A site, producing a bacteriostatic effect.
Chloramphenicol acts on the 50S (peptidyl transferase), vancomycin inhibits
cell-wall peptidoglycan crosslinking, and rifampin inhibits DNA-dependent
RNA polymerase. Understanding ribosomal subunit targets underpins
mechanism-based antibiotic selection and resistance interpretation.
Key words: tetracycline, 30S subunit, protein synthesis inhibition,
bacteriostatic
11.Specialized transduction differs from generalized transduction because:
A. Specialized transduction randomly packages host DNA during the lytic
cycle
B. Specialized transduction involves a temperate (lysogenic) phage that
excises imprecisely and carries only adjacent host genes to new hosts
C. It occurs only during bacterial conjugation
D. It relies on uptake of free DNA from the environment
Answer: B
Rationale: Specialized transduction is mediated by lysogenic phages that
integrate at specific sites; upon induction, imprecise excision can capture
specific host genes adjacent to the prophage and package them into phage
particles, transferring those specific genes to recipient cells. Generalized
, transduction (by lytic phages) can package random pieces of host DNA. The
mechanism has evolutionary significance for gene transfer, including
virulence factors.
Key words: specialized transduction, lysogeny, prophage excision, gene
transfer
12.To culture obligate anaerobic bacteria from a clinical specimen reliably,
which laboratory condition is required?
A. Incubation in ambient air at 37°C
B. Incubation in 5% CO₂ atmosphere only
C. Strict oxygen-free conditions (anaerobic jar/chamber with reducing
agents or palladium catalyst) to maintain low redox potential
D. Microaerophilic environment with reduced O₂ but not zero O₂
Answer: C
Rationale: Obligate anaerobes are intolerant of molecular oxygen and
require oxygen-free conditions for growth; anaerobic chambers or jars with
gas packs or palladium catalysts and reducing media create these conditions.
Microaerophilic setups still have low levels of O₂ and are unsuitable for
strict anaerobes. Proper specimen transport and rapid processing are also
critical because oxygen exposure rapidly kills anaerobes.
Key words: obligate anaerobe, anaerobic chamber, reducing agents, redox
potential
13.Which domain of life is characterized by ether-linked membrane lipids,
unique RNA polymerases, and lack of peptidoglycan in most cell envelopes?
A. Bacteria
B. Archaea
C. Eukarya
D. Viruses
Answer: B
Rationale: Archaea possess distinctive membrane lipids with ether bonds to
isoprenoid chains (rather than bacterial/eukaryotic ester-linked fatty acids),
have RNA polymerases and ribosomal proteins resembling eukaryotes in
some respects, and their cell envelopes typically lack canonical
peptidoglycan (some have pseudopeptidoglycan or S-layers). These
molecular differences justify their classification as a separate domain and
explain physiological adaptations to extreme environments.
Key words: Archaea, ether lipids, pseudopeptidoglycan, domain distinctions
14.In Gram-negative bacteria, quorum sensing most commonly uses which
class of molecules as intercellular signals to coordinate group behaviors like
virulence and biofilm formation?
A. Short peptides similar to cytokines
