Rio Salado Bio 205 - Microbiology Midterm
Exam 2 - Comprehensive Practice Exam
Questions And Correct Answers With
Rationales.pdf
Practice Question Bank & Answer Rationale
THIS PACK CONTAINS
149 exam-style multiple-choice questions. Each question includes the correct answer and a complete
rationale for focused revision.
COVERAGE
This comprehensive midterm exam covers microbial structure and function, microbial genetics, control of
microbial growth, antimicrobial chemotherapy, host-microbe interactions, immunology, and selected clinical
microbiology applications. Questions emphasize application-level reasoning, interpretation of laboratory data,
and integration of core microbiological principles in clinically relevant contexts.
STUDY GUIDE
Recommended duration: 2.5 hours. Passing target: 70% (C or better; A+ target 97%).
HIGHP - Page 1 of 49
,1. A Gram-negative bacillus isolated from a wound is oxidase-positive and produces a
green-blue pigment on King A medium. Which organism is most likely?
[ ] A. Escherichia coli
[ ] B. Pseudomonas aeruginosa
[ ] C. Klebsiella pneumoniae
[ ] D. Proteus mirabilis
CORRECT: B. Pseudomonas aeruginosa
Pseudomonas aeruginosa is an oxidase-positive, Gram-negative bacillus that produces the blue-green
pigment pyocyanin on King A medium. E. coli, Klebsiella, and Proteus are oxidase-negative Enterobacterales
and do not produce pyocyanin.
2. In the Ames test, a chemical causes a 10-fold increase in revertant colonies of
Salmonella typhimurium his strains when rat liver S9 is included. This result most directly
indicates that the chemical is:
[ ] A. Directly bactericidal to Salmonella
[ ] B. A mutagen after metabolic activation
[ ] C. A non-mutagenic carcinogen
[ ] D. An inducer of the SOS response without DNA damage
CORRECT: B. A mutagen after metabolic activation
The Ames test detects reverse mutations; increased revertants with S9 indicate the chemical requires
metabolic activation to become mutagenic. Bactericidal activity would reduce colonies, and non-mutagenic
carcinogens typically yield negative Ames results.
3. A disinfectant with a phenol coefficient of 5 against Salmonella typhi is being compared
to phenol. This value means the disinfectant is:
[ ] A. Five times more effective than phenol under the test conditions
[ ] B. Five times less effective than phenol under the test conditions
[ ] C. Effective only at 5°C
[ ] D. Equally effective as a 5% phenol solution
CORRECT: A. Five times more effective than phenol under the test conditions
The phenol coefficient compares a disinfectant's killing power to phenol; a value of 5 means it is five times
more effective than phenol under the specified test conditions. It does not indicate temperature dependence
or equivalence to 5% phenol.
4. A patient develops severe diarrhea after broad-spectrum antibiotics. Stool testing
reveals a toxin that ADP-ribosylates Rho GTPases, leading to actin disassembly. Which
organism is responsible?
HIGHP - Page 2 of 49
, [ ] A. Clostridioides difficile
[ ] B. Vibrio cholerae
[ ] C. Shigella dysenteriae
[ ] D. Enterotoxigenic Escherichia coli
CORRECT: A. Clostridioides difficile
Clostridioides difficile toxin B (and A) glucosylates and inactivates Rho GTPases, disrupting the cytoskeleton
and causing pseudomembranous colitis after antibiotic use. Cholera toxin and ETEC toxins increase
cAMP/cGMP, and Shiga toxin inhibits protein synthesis.
5. In a phagocytosis assay, neutrophils from a patient show normal chemotaxis and
ingestion but fail to kill ingested Staphylococcus aureus. A defect in which process is
most likely?
[ ] A. Opsonization by complement
[ ] B. Respiratory burst and reactive oxygen species production
[ ] C. Adhesion via selectins
[ ] D. Antigen presentation by MHC class II
CORRECT: B. Respiratory burst and reactive oxygen species production
Normal ingestion but impaired killing suggests a defect in the oxidative burst (e.g., chronic granulomatous
disease). Opsonization and adhesion affect uptake or recruitment, and MHC class II is unrelated to neutrophil
killing.
6. A bacterial isolate is resistant to penicillin due to production of a -lactamase. Which
combination agent would most likely restore susceptibility?
[ ] A. Ampicillin plus vancomycin
[ ] B. Amoxicillin plus clavulanic acid
[ ] C. Cefazolin plus gentamicin
[ ] D. Meropenem plus polymyxin B
CORRECT: B. Amoxicillin plus clavulanic acid
Clavulanic acid is a -lactamase inhibitor that protects amoxicillin from enzymatic hydrolysis, restoring activity.
Vancomycin and gentamicin do not inhibit -lactamases, and meropenem is already stable to many
-lactamases but is not paired with a inhibitor here.
7. A viral outbreak spreads rapidly in a closed community, and many infected individuals
show symptoms after a short incubation. Which viral characteristic most directly explains
the rapid spread?
[ ] A. Enveloped virion with low environmental stability
[ ] B. High basic reproduction number (R0) and efficient respiratory transmission
HIGHP - Page 3 of 49
, [ ] C. Latency with intermittent reactivation
[ ] D. Oncogenic transformation of host cells
CORRECT: B. High basic reproduction number (R0) and efficient respiratory transmission
A high R0 combined with efficient respiratory transmission allows rapid person-to-person spread in closed
populations. Low environmental stability, latency, and oncogenesis do not directly drive rapid acute
outbreaks.
8. A patient with a prosthetic joint develops a chronic infection. Culture grows
Staphylococcus epidermidis producing a polysaccharide matrix. This biofilm primarily:
[ ] A. Enhances antibiotic penetration
[ ] B. Protects bacteria from antibiotics and host defenses
[ ] C. Increases metabolic rate of bacteria
[ ] D. Prevents initial bacterial adherence
CORRECT: B. Protects bacteria from antibiotics and host defenses
Biofilms are extracellular polymeric substance matrices that shield bacteria from antibiotics, disinfectants, and
immune cells, often causing persistent device-related infections. They impede rather than enhance drug
penetration and are associated with reduced metabolic activity.
9. A fungal culture grows a mold with septate hyphae and conidiophores bearing chains
of conidia. Which genus is most likely?
[ ] A. Aspergillus
[ ] B. Candida
[ ] C. Cryptococcus
[ ] D. Rhizopus
CORRECT: A. Aspergillus
Aspergillus is a septate mold that produces conidiophores with chains of conidia. Candida is a yeast,
Cryptococcus is an encapsulated yeast, and Rhizopus is an aseptate mold.
10. A vaccine containing a detoxified bacterial exotoxin that retains antigenicity but lacks
toxicity is best described as a:
[ ] A. Live attenuated vaccine
[ ] B. Toxoid vaccine
[ ] C. Subunit polysaccharide vaccine
[ ] D. DNA vaccine
CORRECT: B. Toxoid vaccine
A toxoid is a chemically inactivated exotoxin that retains immunogenicity but loses toxicity, such as tetanus
HIGHP - Page 4 of 49
Exam 2 - Comprehensive Practice Exam
Questions And Correct Answers With
Rationales.pdf
Practice Question Bank & Answer Rationale
THIS PACK CONTAINS
149 exam-style multiple-choice questions. Each question includes the correct answer and a complete
rationale for focused revision.
COVERAGE
This comprehensive midterm exam covers microbial structure and function, microbial genetics, control of
microbial growth, antimicrobial chemotherapy, host-microbe interactions, immunology, and selected clinical
microbiology applications. Questions emphasize application-level reasoning, interpretation of laboratory data,
and integration of core microbiological principles in clinically relevant contexts.
STUDY GUIDE
Recommended duration: 2.5 hours. Passing target: 70% (C or better; A+ target 97%).
HIGHP - Page 1 of 49
,1. A Gram-negative bacillus isolated from a wound is oxidase-positive and produces a
green-blue pigment on King A medium. Which organism is most likely?
[ ] A. Escherichia coli
[ ] B. Pseudomonas aeruginosa
[ ] C. Klebsiella pneumoniae
[ ] D. Proteus mirabilis
CORRECT: B. Pseudomonas aeruginosa
Pseudomonas aeruginosa is an oxidase-positive, Gram-negative bacillus that produces the blue-green
pigment pyocyanin on King A medium. E. coli, Klebsiella, and Proteus are oxidase-negative Enterobacterales
and do not produce pyocyanin.
2. In the Ames test, a chemical causes a 10-fold increase in revertant colonies of
Salmonella typhimurium his strains when rat liver S9 is included. This result most directly
indicates that the chemical is:
[ ] A. Directly bactericidal to Salmonella
[ ] B. A mutagen after metabolic activation
[ ] C. A non-mutagenic carcinogen
[ ] D. An inducer of the SOS response without DNA damage
CORRECT: B. A mutagen after metabolic activation
The Ames test detects reverse mutations; increased revertants with S9 indicate the chemical requires
metabolic activation to become mutagenic. Bactericidal activity would reduce colonies, and non-mutagenic
carcinogens typically yield negative Ames results.
3. A disinfectant with a phenol coefficient of 5 against Salmonella typhi is being compared
to phenol. This value means the disinfectant is:
[ ] A. Five times more effective than phenol under the test conditions
[ ] B. Five times less effective than phenol under the test conditions
[ ] C. Effective only at 5°C
[ ] D. Equally effective as a 5% phenol solution
CORRECT: A. Five times more effective than phenol under the test conditions
The phenol coefficient compares a disinfectant's killing power to phenol; a value of 5 means it is five times
more effective than phenol under the specified test conditions. It does not indicate temperature dependence
or equivalence to 5% phenol.
4. A patient develops severe diarrhea after broad-spectrum antibiotics. Stool testing
reveals a toxin that ADP-ribosylates Rho GTPases, leading to actin disassembly. Which
organism is responsible?
HIGHP - Page 2 of 49
, [ ] A. Clostridioides difficile
[ ] B. Vibrio cholerae
[ ] C. Shigella dysenteriae
[ ] D. Enterotoxigenic Escherichia coli
CORRECT: A. Clostridioides difficile
Clostridioides difficile toxin B (and A) glucosylates and inactivates Rho GTPases, disrupting the cytoskeleton
and causing pseudomembranous colitis after antibiotic use. Cholera toxin and ETEC toxins increase
cAMP/cGMP, and Shiga toxin inhibits protein synthesis.
5. In a phagocytosis assay, neutrophils from a patient show normal chemotaxis and
ingestion but fail to kill ingested Staphylococcus aureus. A defect in which process is
most likely?
[ ] A. Opsonization by complement
[ ] B. Respiratory burst and reactive oxygen species production
[ ] C. Adhesion via selectins
[ ] D. Antigen presentation by MHC class II
CORRECT: B. Respiratory burst and reactive oxygen species production
Normal ingestion but impaired killing suggests a defect in the oxidative burst (e.g., chronic granulomatous
disease). Opsonization and adhesion affect uptake or recruitment, and MHC class II is unrelated to neutrophil
killing.
6. A bacterial isolate is resistant to penicillin due to production of a -lactamase. Which
combination agent would most likely restore susceptibility?
[ ] A. Ampicillin plus vancomycin
[ ] B. Amoxicillin plus clavulanic acid
[ ] C. Cefazolin plus gentamicin
[ ] D. Meropenem plus polymyxin B
CORRECT: B. Amoxicillin plus clavulanic acid
Clavulanic acid is a -lactamase inhibitor that protects amoxicillin from enzymatic hydrolysis, restoring activity.
Vancomycin and gentamicin do not inhibit -lactamases, and meropenem is already stable to many
-lactamases but is not paired with a inhibitor here.
7. A viral outbreak spreads rapidly in a closed community, and many infected individuals
show symptoms after a short incubation. Which viral characteristic most directly explains
the rapid spread?
[ ] A. Enveloped virion with low environmental stability
[ ] B. High basic reproduction number (R0) and efficient respiratory transmission
HIGHP - Page 3 of 49
, [ ] C. Latency with intermittent reactivation
[ ] D. Oncogenic transformation of host cells
CORRECT: B. High basic reproduction number (R0) and efficient respiratory transmission
A high R0 combined with efficient respiratory transmission allows rapid person-to-person spread in closed
populations. Low environmental stability, latency, and oncogenesis do not directly drive rapid acute
outbreaks.
8. A patient with a prosthetic joint develops a chronic infection. Culture grows
Staphylococcus epidermidis producing a polysaccharide matrix. This biofilm primarily:
[ ] A. Enhances antibiotic penetration
[ ] B. Protects bacteria from antibiotics and host defenses
[ ] C. Increases metabolic rate of bacteria
[ ] D. Prevents initial bacterial adherence
CORRECT: B. Protects bacteria from antibiotics and host defenses
Biofilms are extracellular polymeric substance matrices that shield bacteria from antibiotics, disinfectants, and
immune cells, often causing persistent device-related infections. They impede rather than enhance drug
penetration and are associated with reduced metabolic activity.
9. A fungal culture grows a mold with septate hyphae and conidiophores bearing chains
of conidia. Which genus is most likely?
[ ] A. Aspergillus
[ ] B. Candida
[ ] C. Cryptococcus
[ ] D. Rhizopus
CORRECT: A. Aspergillus
Aspergillus is a septate mold that produces conidiophores with chains of conidia. Candida is a yeast,
Cryptococcus is an encapsulated yeast, and Rhizopus is an aseptate mold.
10. A vaccine containing a detoxified bacterial exotoxin that retains antigenicity but lacks
toxicity is best described as a:
[ ] A. Live attenuated vaccine
[ ] B. Toxoid vaccine
[ ] C. Subunit polysaccharide vaccine
[ ] D. DNA vaccine
CORRECT: B. Toxoid vaccine
A toxoid is a chemically inactivated exotoxin that retains immunogenicity but loses toxicity, such as tetanus
HIGHP - Page 4 of 49
