BIOD 171 Microbiology Module 6 Exam | Latest Update 2026–2027 |
Questions and Verified Answers with Rationales | 100% Correct
1. What is the definition of a narrow‑spectrum antibiotic?
A. An antibiotic that is effective against both Gram‑positive and Gram‑negative bacteria
B. An antibiotic that targets a limited group of bacteria (e.g., only Gram‑positive or only a few species)
C. An antibiotic that kills fungi
D. An antibiotic that is only used topically
Correct Answer: B
Rationale: Narrow‑spectrum antibiotics are effective against a small subset of bacteria, which helps
reduce disruption of normal flora and limits resistance development.
2. Which of the following is a bactericidal antibiotic?
A. Tetracycline
B. Penicillin
C. Erythromycin
D. Chloramphenicol
Correct Answer: B
Rationale: Penicillin is bactericidal (kills bacteria) by inhibiting cell wall synthesis. Tetracycline,
erythromycin, and chloramphenicol are bacteriostatic (inhibit growth).
3. The mechanism of action of sulfonamides involves:
A. Inhibition of cell wall synthesis
B. Inhibition of folic acid synthesis
C. Disruption of the cell membrane
D. Inhibition of protein synthesis at the 50S ribosome
Correct Answer: B
Rationale: Sulfonamides are competitive inhibitors of dihydropteroate synthase, blocking folic acid
synthesis in bacteria.
,4. Which antibiotic is known to cause tooth discoloration in children?
A. Amoxicillin
B. Tetracycline
C. Ciprofloxacin
D. Gentamicin
Correct Answer: B
Rationale: Tetracycline binds to calcium in developing teeth, causing permanent brown discoloration. It
is contraindicated in children <8 years and pregnant women.
5. The Kirby‑Bauer disk diffusion test is used to determine:
A. The minimum inhibitory concentration (MIC) of an antibiotic
B. The susceptibility of a bacterium to various antibiotics
C. The bacterial cell count
D. The presence of bacterial toxins
Correct Answer: B
Rationale: Kirby‑Bauer test measures the zone of inhibition around antibiotic disks to classify bacteria as
susceptible, intermediate, or resistant.
6. A patient has a methicillin‑resistant Staphylococcus aureus (MRSA) infection. Which of the following is
the most appropriate treatment?
A. Penicillin G
B. Vancomycin
C. Ampicillin
D. Cephalexin
Correct Answer: B
Rationale: MRSA is resistant to all penicillins and most cephalosporins. Vancomycin is the drug of choice
for serious MRSA infections.
7. Which of the following statements about antimicrobial resistance is true?
A. Bacteria can acquire resistance genes via transduction, transformation, or conjugation
,B. Resistance genes are never found on plasmids
C. Misuse of antibiotics has no effect on resistance development
D. Resistance only occurs through mutation of chromosomal DNA
Correct Answer: A
Rationale: Horizontal gene transfer (transduction, transformation, conjugation) spreads resistance
genes, often on plasmids or transposons.
8. The mechanism of action of beta‑lactam antibiotics (e.g., penicillins, cephalosporins) is:
A. Inhibition of protein synthesis by binding to 30S ribosome
B. Inhibition of nucleic acid synthesis
C. Inhibition of cell wall synthesis by binding to penicillin‑binding proteins (PBPs)
D. Disruption of the bacterial cell membrane
Correct Answer: C
Rationale: Beta‑lactams inhibit transpeptidases (PBPs) that cross‑link peptidoglycan, leading to cell lysis.
9. Which of the following is an example of an aminoglycoside antibiotic?
A. Gentamicin
B. Azithromycin
C. Doxycycline
D. Clindamycin
Correct Answer: A
Rationale: Gentamicin is an aminoglycoside. Azithromycin is a macrolide; doxycycline is a tetracycline;
clindamycin is a lincosamide.
10. A major side effect of aminoglycosides is:
A. Hepatotoxicity
B. Nephrotoxicity and ototoxicity
C. Cardiotoxicity
D. Photosensitivity
, Correct Answer: B
Rationale: Aminoglycosides accumulate in renal tubular cells and hair cells of the inner ear, causing
dose‑dependent nephrotoxicity and irreversible hearing loss/vestibular damage.
11. Which of the following is a bactericidal antibiotic that inhibits folate synthesis?
A. Trimethoprim (when combined with sulfamethoxazole)
B. Erythromycin
C. Vancomycin
D. Linezolid
Correct Answer: A
Rationale: Trimethoprim inhibits dihydrofolate reductase; when combined with sulfamethoxazole (sulfa
drug), the sequential blockade is bactericidal.
12. The Etest is used to:
A. Quantify the minimal inhibitory concentration (MIC) of an antibiotic
B. Identify bacterial species
C. Determine the bacterial growth curve
D. Detect viral particles
Correct Answer: A
Rationale: Etest uses a plastic strip with a gradient of antibiotic; the MIC is read where the ellipse of
inhibition intersects the strip.
13. Which of the following mechanisms confers resistance to beta‑lactam antibiotics?
A. Production of beta‑lactamase enzymes
B. Modification of the 50S ribosome
C. Efflux pumps for tetracycline only
D. Overproduction of folic acid
Correct Answer: A
Rationale: Beta‑lactamases hydrolyze the beta‑lactam ring, inactivating penicillins and cephalosporins.
Other mechanisms include altered PBPs (MRSA) and efflux pumps.
Questions and Verified Answers with Rationales | 100% Correct
1. What is the definition of a narrow‑spectrum antibiotic?
A. An antibiotic that is effective against both Gram‑positive and Gram‑negative bacteria
B. An antibiotic that targets a limited group of bacteria (e.g., only Gram‑positive or only a few species)
C. An antibiotic that kills fungi
D. An antibiotic that is only used topically
Correct Answer: B
Rationale: Narrow‑spectrum antibiotics are effective against a small subset of bacteria, which helps
reduce disruption of normal flora and limits resistance development.
2. Which of the following is a bactericidal antibiotic?
A. Tetracycline
B. Penicillin
C. Erythromycin
D. Chloramphenicol
Correct Answer: B
Rationale: Penicillin is bactericidal (kills bacteria) by inhibiting cell wall synthesis. Tetracycline,
erythromycin, and chloramphenicol are bacteriostatic (inhibit growth).
3. The mechanism of action of sulfonamides involves:
A. Inhibition of cell wall synthesis
B. Inhibition of folic acid synthesis
C. Disruption of the cell membrane
D. Inhibition of protein synthesis at the 50S ribosome
Correct Answer: B
Rationale: Sulfonamides are competitive inhibitors of dihydropteroate synthase, blocking folic acid
synthesis in bacteria.
,4. Which antibiotic is known to cause tooth discoloration in children?
A. Amoxicillin
B. Tetracycline
C. Ciprofloxacin
D. Gentamicin
Correct Answer: B
Rationale: Tetracycline binds to calcium in developing teeth, causing permanent brown discoloration. It
is contraindicated in children <8 years and pregnant women.
5. The Kirby‑Bauer disk diffusion test is used to determine:
A. The minimum inhibitory concentration (MIC) of an antibiotic
B. The susceptibility of a bacterium to various antibiotics
C. The bacterial cell count
D. The presence of bacterial toxins
Correct Answer: B
Rationale: Kirby‑Bauer test measures the zone of inhibition around antibiotic disks to classify bacteria as
susceptible, intermediate, or resistant.
6. A patient has a methicillin‑resistant Staphylococcus aureus (MRSA) infection. Which of the following is
the most appropriate treatment?
A. Penicillin G
B. Vancomycin
C. Ampicillin
D. Cephalexin
Correct Answer: B
Rationale: MRSA is resistant to all penicillins and most cephalosporins. Vancomycin is the drug of choice
for serious MRSA infections.
7. Which of the following statements about antimicrobial resistance is true?
A. Bacteria can acquire resistance genes via transduction, transformation, or conjugation
,B. Resistance genes are never found on plasmids
C. Misuse of antibiotics has no effect on resistance development
D. Resistance only occurs through mutation of chromosomal DNA
Correct Answer: A
Rationale: Horizontal gene transfer (transduction, transformation, conjugation) spreads resistance
genes, often on plasmids or transposons.
8. The mechanism of action of beta‑lactam antibiotics (e.g., penicillins, cephalosporins) is:
A. Inhibition of protein synthesis by binding to 30S ribosome
B. Inhibition of nucleic acid synthesis
C. Inhibition of cell wall synthesis by binding to penicillin‑binding proteins (PBPs)
D. Disruption of the bacterial cell membrane
Correct Answer: C
Rationale: Beta‑lactams inhibit transpeptidases (PBPs) that cross‑link peptidoglycan, leading to cell lysis.
9. Which of the following is an example of an aminoglycoside antibiotic?
A. Gentamicin
B. Azithromycin
C. Doxycycline
D. Clindamycin
Correct Answer: A
Rationale: Gentamicin is an aminoglycoside. Azithromycin is a macrolide; doxycycline is a tetracycline;
clindamycin is a lincosamide.
10. A major side effect of aminoglycosides is:
A. Hepatotoxicity
B. Nephrotoxicity and ototoxicity
C. Cardiotoxicity
D. Photosensitivity
, Correct Answer: B
Rationale: Aminoglycosides accumulate in renal tubular cells and hair cells of the inner ear, causing
dose‑dependent nephrotoxicity and irreversible hearing loss/vestibular damage.
11. Which of the following is a bactericidal antibiotic that inhibits folate synthesis?
A. Trimethoprim (when combined with sulfamethoxazole)
B. Erythromycin
C. Vancomycin
D. Linezolid
Correct Answer: A
Rationale: Trimethoprim inhibits dihydrofolate reductase; when combined with sulfamethoxazole (sulfa
drug), the sequential blockade is bactericidal.
12. The Etest is used to:
A. Quantify the minimal inhibitory concentration (MIC) of an antibiotic
B. Identify bacterial species
C. Determine the bacterial growth curve
D. Detect viral particles
Correct Answer: A
Rationale: Etest uses a plastic strip with a gradient of antibiotic; the MIC is read where the ellipse of
inhibition intersects the strip.
13. Which of the following mechanisms confers resistance to beta‑lactam antibiotics?
A. Production of beta‑lactamase enzymes
B. Modification of the 50S ribosome
C. Efflux pumps for tetracycline only
D. Overproduction of folic acid
Correct Answer: A
Rationale: Beta‑lactamases hydrolyze the beta‑lactam ring, inactivating penicillins and cephalosporins.
Other mechanisms include altered PBPs (MRSA) and efflux pumps.
