1|Page
Topical Antimicrobials 2026/2027 Actual Questions
with Verified Answers | Grade A Study Guide
1. A microbiology report indicates a bacterium stains purple and has a thick
peptidoglycan cell wall. This describes a:
A. Gram-negative organism
B. Gram-positive organism
C. Virus
D. Fungus
CORRECT ANSWER: B
RATIONALE: Gram-positive bacteria retain the crystal violet stain (appearing
purple) due to their thick peptidoglycan cell wall. This is a fundamental
characteristic differentiating them from gram-negative bacteria.
2. A contact lens wearer presents with a central corneal ulcer. While awaiting
culture results, empiric therapy should primarily target:
,2|Page
A. Staphylococcus aureus
B. Pseudomonas aeruginosa
C. Streptococcus pneumoniae
D. Haemophilus influenzae
CORRECT ANSWER: B
RATIONALE: Pseudomonas aeruginosa is a gram-negative rod strongly
associated with contact lens-related corneal ulcers due to its ability to
adhere to lenses and produce destructive enzymes. Empiric therapy must
cover this virulent organism.
3. The Minimum Inhibitory Concentration (MIC) of a drug for a specific
bacterium is 2 mcg/mL. The achievable concentration in the tissue is 8
mcg/mL. This indicates the bacterium is:
A. Resistant
B. Susceptible
C. Intermediate
D. Virulent
,3|Page
CORRECT ANSWER: B
RATIONALE: If the drug concentration attainable at the site of infection is
higher than the MIC, the organism is considered susceptible. Here, 8 mcg/mL
(tissue) > 2 mcg/mL (MIC), indicating susceptibility.
4. Bactericidal drugs are most effective when:
A. The bacteria are dormant.
B. Used concurrently with a bacteriostatic drug.
C. The bacteria are actively dividing.
D. The patient is immunocompromised.
CORRECT ANSWER: C
RATIONALE: Bactericidal drugs (e.g., fluoroquinolones, aminoglycosides)
often target processes like cell wall or DNA synthesis, which are most active
during bacterial replication. Their killing efficacy is highest against dividing
organisms.
5. A patient with a severe gram-positive corneal ulcer is prescribed a topical
antibiotic that inhibits cell wall synthesis by binding to peptidoglycan
, 4|Page
precursors. This describes the mechanism of:
A. Fluoroquinolones
B. Macrolides
C. Vancomycin
D. Sulfonamides
CORRECT ANSWER: C
RATIONALE: Vancomycin, a glycopeptide, inhibits cell wall synthesis by
binding to the D-alanyl-D-alanine portion of peptidoglycan precursors,
preventing cross-linking. It is used for serious gram-positive infections,
including MRSA.
6. A patient presents with blepharitis characterized by red, crusty lid margins.
The most appropriate topical antibiotic ointment, effective against common
gram-positive skin flora, is:
A. Polymyxin B
B. Bacitracin
C. Gentamicin
Topical Antimicrobials 2026/2027 Actual Questions
with Verified Answers | Grade A Study Guide
1. A microbiology report indicates a bacterium stains purple and has a thick
peptidoglycan cell wall. This describes a:
A. Gram-negative organism
B. Gram-positive organism
C. Virus
D. Fungus
CORRECT ANSWER: B
RATIONALE: Gram-positive bacteria retain the crystal violet stain (appearing
purple) due to their thick peptidoglycan cell wall. This is a fundamental
characteristic differentiating them from gram-negative bacteria.
2. A contact lens wearer presents with a central corneal ulcer. While awaiting
culture results, empiric therapy should primarily target:
,2|Page
A. Staphylococcus aureus
B. Pseudomonas aeruginosa
C. Streptococcus pneumoniae
D. Haemophilus influenzae
CORRECT ANSWER: B
RATIONALE: Pseudomonas aeruginosa is a gram-negative rod strongly
associated with contact lens-related corneal ulcers due to its ability to
adhere to lenses and produce destructive enzymes. Empiric therapy must
cover this virulent organism.
3. The Minimum Inhibitory Concentration (MIC) of a drug for a specific
bacterium is 2 mcg/mL. The achievable concentration in the tissue is 8
mcg/mL. This indicates the bacterium is:
A. Resistant
B. Susceptible
C. Intermediate
D. Virulent
,3|Page
CORRECT ANSWER: B
RATIONALE: If the drug concentration attainable at the site of infection is
higher than the MIC, the organism is considered susceptible. Here, 8 mcg/mL
(tissue) > 2 mcg/mL (MIC), indicating susceptibility.
4. Bactericidal drugs are most effective when:
A. The bacteria are dormant.
B. Used concurrently with a bacteriostatic drug.
C. The bacteria are actively dividing.
D. The patient is immunocompromised.
CORRECT ANSWER: C
RATIONALE: Bactericidal drugs (e.g., fluoroquinolones, aminoglycosides)
often target processes like cell wall or DNA synthesis, which are most active
during bacterial replication. Their killing efficacy is highest against dividing
organisms.
5. A patient with a severe gram-positive corneal ulcer is prescribed a topical
antibiotic that inhibits cell wall synthesis by binding to peptidoglycan
, 4|Page
precursors. This describes the mechanism of:
A. Fluoroquinolones
B. Macrolides
C. Vancomycin
D. Sulfonamides
CORRECT ANSWER: C
RATIONALE: Vancomycin, a glycopeptide, inhibits cell wall synthesis by
binding to the D-alanyl-D-alanine portion of peptidoglycan precursors,
preventing cross-linking. It is used for serious gram-positive infections,
including MRSA.
6. A patient presents with blepharitis characterized by red, crusty lid margins.
The most appropriate topical antibiotic ointment, effective against common
gram-positive skin flora, is:
A. Polymyxin B
B. Bacitracin
C. Gentamicin
