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Question 1. Which structural feature distinguishes Gram-negative bacteria from Gram-positive bacteria? A) Thick peptidoglycan layer B) Presence of teichoic acids C) Outer membrane containing lipopolysaccharide D) Absence of a cell wall Answer: C Explanation: Gram-negative organisms possess an outer membrane rich in lipopolysaccharide (LPS) that is absent in Gram-positive bacteria, which instead have a thick peptidoglycan layer and teichoic acids. Question 2. Mycoplasma pneumoniae lacks which of the following cellular components, making it intrinsically resistant to β-lactams? A) Ribosomes B) Cell wall containing peptidoglycan C) DNA gyrase D) Cytoplasmic membrane Answer: B Explanation: Mycoplasma species do not have a cell wall; therefore, drugs that target cell-wall synthesis, such as β-lactams, are ineffective. Question 3. Which anaerobic organism is most commonly isolated from intra-abdominal infections above the diaphragm? A) Bacteroides fragilis B) Clostridium perfringens C) Peptostreptococcus spp.
D) Fusobacterium necrophorum Answer: A Explanation: Bacteroides fragilis predominates in polymicrobial intra-abdominal infections, especially those involving the upper gastrointestinal tract. Question 4. In antimicrobial susceptibility testing, a MIC that falls at the breakpoint for a drug is considered: A) Susceptible B) Intermediate C) Resistant D) Undetermined Answer: B Explanation: Breakpoints divide the MIC range into susceptible, intermediate, and resistant categories; values at the breakpoint are classified as intermediate. Question 5. Which rapid diagnostic technology uses mass spectrometry to identify organisms directly from positive blood culture broths? A) PCR B) MALDI-TOF C) Next-generation sequencing D) Flow cytometry Answer: B
B. Fluoroquinolones C. β-lactams D. Lipopeptides Answer: C Explanation: β-lactam antibiotics exhibit time-dependent bactericidal activity; maintaining serum concentrations above the MIC for a sufficient portion of the dosing interval is critical. Question 9. Post-antibiotic effect (PAE) is most pronounced with which of the following agents? A) Penicillin G B) Ciprofloxacin C) Vancomycin D) Azithromycin Answer: D Explanation: Macrolides, especially azithromycin, display a long PAE, allowing extended dosing intervals despite time-dependent activity. Question 10. Which penicillin is classified as an antistaphylococcal penicillin? A) Ampicillin B) Oxacillin C) Piperacillin D) Ticarcillin Answer: B
Explanation: Oxacillin (and nafcillin) are penicillinase-resistant, antistaphylococcal agents effective against MSS Staphylococcus aureus. Question 11. Ceftaroline is unique among cephalosporins because it has activity against: A) ESBL-producing E. coli B) Carbapenem-resistant Acinetobacter C) MRSA D) Pseudomonas aeruginosa Answer: C Explanation: Ceftaroline binds PBP2a, providing activity against methicillin-resistant Staphylococcus aureus (MRSA). Question 12. Which carbapenem lacks reliable activity against Pseudomonas aeruginosa and Acinetobacter baumannii? A) Meropenem B) Imipenem-cilastatin C) Doripenem D) Ertapenem Answer: D Explanation: Ertapenem has a narrower spectrum and does not cover non-fermenting Gram-negatives such as Pseudomonas and Acinetobacter. Question 13. Aztreonam is the preferred β-lactam for patients with a severe penicillin allergy when coverage of which organism is required? A) MRSA
Explanation: The bactericidal synergy of a cell-wall agent (ampicillin) with an aminoglycoside (gentamicin) is the cornerstone of treatment for Enterococcus endocarditis. Question 16. Doxycycline is the drug of choice for which of the following tick-borne diseases? A) Rocky Mountain spotted fever B) Lyme disease (early) C) Ehrlichiosis D) All of the above Answer: D Explanation: Doxycycline is highly effective against Rickettsia rickettsii, Borrelia burgdorferi (early Lyme), and Ehrlichia spp., making it the preferred therapy for most tick-borne infections. Question 17. Tigecycline lacks activity against which organism? A) Acinetobacter baumannii B) Enterococcus faecalis C) Pseudomonas aeruginosa D) Staphylococcus aureus Answer: C Explanation: Tigecycline’s spectrum excludes Pseudomonas aeruginosa and Proteus spp.; it retains activity against many other multidrug-resistant Gram-negatives. **Question 18. Macrolides are associated with which cardiac adverse effect? **
A) Bradycardia B) QT interval prolongation C) Atrioventricular block D) ST-segment elevation Answer: B Explanation: Macrolides (especially erythromycin, clarithromycin, azithromycin) can inhibit cardiac potassium channels, leading to QT prolongation and risk of torsades de pointes. Question 19. Which macrolide has the highest potential for CYP3A drug-drug interactions? A) Azithromycin B) Clarithromycin C) Roxithromycin D) Spiramycin Answer: B Explanation: Clarithromycin is a strong CYP3A4 inhibitor, whereas azithromycin has minimal CYP involvement. Question 20. Clindamycin therapy increases the risk of which nosocomial infection? A) Staphylococcus aureus bacteremia B) Clostridioides difficile colitis C) Vancomycin-resistant Enterococcus (VRE) infection D) Pseudomonas aeruginosa pneumonia
A) CYP1A
B) CYP2D
C) CYP3A
D) CYP2C
Answer: C Explanation: Rifampin is a potent inducer of CYP3A4 (as well as other enzymes), decreasing plasma concentrations of many co-administered drugs. Question 24. Vancomycin therapeutic monitoring is now recommended using which PK/PD parameter? A) Peak concentration (Cmax) B) Trough concentration only C) Area under the curve to MIC (AUC/MIC) D) Time above MIC (T > MIC) Answer: C Explanation: Recent guidelines favor AUC/MIC (target 400–600) for vancomycin to improve efficacy while reducing nephrotoxicity, rather than relying solely on trough levels. Question 25. Daptomycin is inactivated by: A) β-lactamases B) Pulmonary surfactant C) Gastric acid D) Renal tubular secretion Answer: B
Explanation: Daptomycin binds to surfactant in the lungs, rendering it ineffective for pneumonia; it is used for bloodstream and skin infections. Question 26. Trimethoprim-sulfamethoxazole dosing is based on the amount of: A) Sulfamethoxazole component B) Trimethoprim component C) Total weight of the combination D) Patient’s creatinine clearance Answer: B Explanation: Dosing recommendations for Bactrim are expressed in milligrams of trimethoprim (e.g., 1 tablet = 80 mg TMP/400 mg SMX). Question 27. Which azole antifungal is most associated with visual disturbances? A) Fluconazole B) Itraconazole C) Voriconazole D) Posaconazole Answer: C Explanation: Voriconazole can cause photopsia, blurred vision, and altered color perception in up to 30 % of patients. Question 28. Posaconazole’s oral absorption is highly dependent on: A) Food intake and gastric acidity B) Renal function
Explanation: Conventional amphotericin B can cause dose-dependent renal injury and acute infusion reactions (fever, chills, rigors), often described as “shake-and-bake”. Question 31. Acyclovir dosing must be adjusted in patients with: A) Severe hypertension B) Renal impairment C) Hyperlipidemia D) Diabetes mellitus Answer: B Explanation: Acyclovir is eliminated renally; accumulation in renal failure increases the risk of crystal-induced nephropathy, necessitating dose reduction. Question 32. The optimal timing for initiating oseltamivir in influenza is: A) Within 48 hours of symptom onset B) After the first week of illness C) Only after a positive rapid antigen test D) Only for hospitalized patients Answer: A Explanation: Early treatment (≤48 h) reduces symptom duration and complications; later initiation offers limited benefit. Question 33. Prior to initiating abacavir-containing ART, clinicians must screen for: A. Hepatitis B surface antigen B. HLA-B*5701 allele
C. Serum creatinine clearance D. HIV-1 RNA viral load Answer: B Explanation: HLA-B*5701 positivity predicts hypersensitivity to abacavir; screening prevents severe reactions. Question 34. Metronidazole’s disulfiram-like reaction is caused by inhibition of: A. Cytochrome P450 2D B. Aldehyde dehydrogenase C. Monoamine oxidase D. Acetylcholinesterase Answer: B Explanation: Metronidazole interferes with aldehyde dehydrogenase, leading to accumulation of acetaldehyde when alcohol is consumed, producing flushing, tachycardia, and nausea. Question 35. According to CURB-65, a score of 3 or higher in CAP warrants: A. Outpatient oral therapy B. Hospital admission, possibly ICU C. No antibiotics, watchful waiting D. Immediate bronchoscopy Answer: B Explanation: CURB- 65 ≥ 3 predicts severe pneumonia with high mortality; patients should be hospitalized, and many require ICU-level care.
C) Necessity of antitubercular therapy D) Use of antiviral agents Answer: B Explanation: Purulent SSTIs (abscesses, cellulitis with pus) often need incision and drainage, whereas non-purulent cellulitis is treated with antibiotics alone. Question 39. Early surgical debridement is the cornerstone of treatment for: A) Necrotizing fasciitis B) Simple cellulitis C) Impetigo D) Folliculitis Answer: A Explanation: Necrotizing fasciitis progresses rapidly; prompt surgery combined with broad-spectrum antibiotics improves survival. Question 40. Empiric therapy for bacterial meningitis in adults aged 18- 50 includes: A) Vancomycin + Ceftriaxone + Ampicillin B) Vancomycin + Ceftriaxone + Dexamethasone C) Meropenem + Gentamicin + Dexamethasone D) Cefepime + Linezolid Answer: B
Explanation: Adults 18-50 are covered for S. pneumoniae (ceftriaxone) and potential resistant Strep pneumoniae (vancomycin); dexamethasone reduces neurologic complications when given before or with the first dose. Question 41. In intra-abdominal infections, adequate source control is defined as: A) Immediate antibiotic administration only B) Drainage or removal of infected tissue in addition to antibiotics C) Use of probiotics D) Switching from IV to PO therapy within 24 h Answer: B Explanation: Successful management requires both antimicrobial therapy and physical removal/drainage of the infection source. Question 42. ESBL-producing Enterobacteriaceae are best treated with: A) Piperacillin-tazobactam B) Cefepime C) Carbapenems D. Ciprofloxacin Answer: C Explanation: Carbapenems retain activity against ESBL producers; other β-lactams are hydrolyzed by ESBL enzymes. Question 43. The primary mechanism of resistance in MRSA is: A) Production of β-lactamase B) Altered penicillin-binding protein 2a (PBP2a)
Question 46. Which drug requires dose adjustment for both renal and hepatic impairment? A) Levofloxacin B) Metronidazole C) Vancomycin D) Azithromycin Answer: B Explanation: Metronidazole is metabolized hepatically and eliminated renally; dose reductions are needed in both organ dysfunctions. Question 47. In a patient with a documented penicillin allergy, cross-reactivity with which β-lactam is highest? A) Aztreonam B) Cephalexin C) Ceftaroline D) Carbapenems Answer: B Explanation: First-generation cephalosporins share the R1 side chain with penicillins, resulting in the highest cross-reactivity (~10 %). Aztreonam has negligible cross-reactivity. Question 48. De-escalation of antimicrobial therapy refers to: A) Switching from oral to IV route B) Narrowing the spectrum based on culture results C) Adding a second agent for synergy
D) Extending the duration of therapy Answer: B Explanation: De-escalation involves reducing antimicrobial breadth (e.g., from broad-spectrum carbapenem to targeted agent) once microbiology data are available. Question 49. The IV-to-PO conversion is appropriate when: A) Patient is afebrile for ≥ 48 h, tolerating oral intake, and has a functioning GI tract B) Pathogen is resistant to all oral agents C) Serum drug levels are undetectable D) The infection is a meningitis Answer: A Explanation: Criteria for step-down include clinical stability, ability to absorb oral medication, and a pathogen susceptible to an oral formulation. Question 50. Daptomycin should never be used for which infection? A) Bacteremia caused by MRSA B) Complicated skin and soft-tissue infection (cSSTI) C) Hospital-acquired pneumonia D) Endocarditis due to Enterococcus Answer: C Explanation: Pulmonary surfactant inactivates daptomycin, making it ineffective for pneumonia.
