Pharm.D. Doctor of Pharmacy Microbiology and Infectious Diseases 2 — Questions and Answers
Question 1: What is the primary molecular mechanism of methicillin resistance in MRSA?
- Constitutive beta-lactamase overproduction
- Acquisition of mecA gene encoding altered PBP2a (Correct answer)
- Efflux pump overexpression reducing intracellular drug concentration
- Reduced outer membrane permeability to beta-lactams
Correct answer: Acquisition of mecA gene encoding altered PBP2a
MRSA acquires the mecA gene (carried on SCCmec mobile elements), which encodes PBP2a, an altered penicillin-binding protein with very low affinity for all beta-lactam antibiotics.
Question 2: Which antibiotic is the preferred treatment for infections caused by KPC-producing carbapenem-resistant Enterobacteriaceae (CRE)?
- Meropenem + colistin
- Ceftazidime-avibactam (Correct answer)
- Piperacillin-tazobactam
- Tigecycline monotherapy
Correct answer: Ceftazidime-avibactam
Ceftazidime-avibactam is preferred for KPC-producing CRE because avibactam inhibits serine-based KPC enzymes, restoring ceftazidime's antibacterial activity against resistant organisms.
Question 3: What is the recommended first-line regimen for Helicobacter pylori eradication in regions with low clarithromycin resistance (below 15%)?
- PPI + amoxicillin + clarithromycin for 14 days (Correct answer)
- H2 blocker + metronidazole + tetracycline for 7 days
- PPI + vancomycin + azithromycin for 10 days
- Bismuth + ciprofloxacin + metronidazole for 14 days
Correct answer: PPI + amoxicillin + clarithromycin for 14 days
Clarithromycin-based triple therapy (PPI + amoxicillin + clarithromycin for 14 days) is first-line for H. pylori eradication where clarithromycin resistance rates are below 15%.
Question 4: Which antiviral neuraminidase inhibitor is approved for treatment of both influenza A and B when initiated within 48 hours of symptom onset?
- Acyclovir
- Oseltamivir (Correct answer)
- Ribavirin
- Amantadine
Correct answer: Oseltamivir
Oseltamivir (Tamiflu) is a neuraminidase inhibitor effective against both influenza A and B that reduces symptom duration by approximately one day when initiated within 48 hours of onset.
Question 5: What is the drug of choice for both prophylaxis and treatment of Pneumocystis jirovecii pneumonia (PCP) in HIV-infected patients with CD4 count below 200 cells/μL?
- Fluconazole
- Trimethoprim-sulfamethoxazole (TMP-SMX) (Correct answer)
- IV pentamidine
- Atovaquone
Correct answer: Trimethoprim-sulfamethoxazole (TMP-SMX)
TMP-SMX is the drug of choice for both PCP prophylaxis and treatment, as it inhibits two sequential steps in folate synthesis in P. jirovecii and achieves superior outcomes compared to alternatives.
Question 6: Which lipoglycopeptide antibiotic has a half-life of approximately 8.5 days, enabling a single-dose or two-dose treatment course for acute bacterial skin infections?
- Vancomycin
- Dalbavancin (Correct answer)
- Telavancin
- Daptomycin
Correct answer: Dalbavancin
Dalbavancin has an exceptionally long half-life (~8.5 days), enabling a single 1,500 mg IV dose or a two-dose regimen for acute bacterial skin and skin structure infections caused by gram-positive organisms.
Question 7: Which isolation precaution category is required for a patient admitted with confirmed active pulmonary tuberculosis?
- Contact precautions with gown and gloves
- Droplet precautions with surgical mask
- Airborne precautions with negative pressure room and N95 respirator (Correct answer)
- Standard precautions only
Correct answer: Airborne precautions with negative pressure room and N95 respirator
Active pulmonary TB requires airborne precautions because M. tuberculosis spreads via droplet nuclei (<5 μm) that remain suspended in air and can travel long distances in ventilated spaces.
