Antimicrobial Mechanisms Practice Test

A 62-year-old man with severe CKD (eGFR 18) presents with dysuria and frequency. UA shows pyuria; urine culture grows ESBL-producing E. coli. Because of renal impairment, nitrofurantoin is avoided, and he receives a single dose of fosfomycin. Which of the following mechanisms explains fosfomycin’s antibacterial action? (Creatinine 3.4 mg/dL; afebrile; no flank pain.)

A 67-year-old man in the ICU develops ventilator-associated pneumonia 6 days after intubation. He has fever 39.2°C, purulent sputum, and worsening hypoxemia. CXR shows new right lower-lobe consolidation. WBC 18,500/µL. Sputum Gram stain shows many neutrophils and gram-negative rods; culture grows Pseudomonas aeruginosa resistant to cefepime and piperacillin-tazobactam but susceptible to meropenem. He is started on meropenem. Which of the following mechanisms explains this drug’s activity against this pathogen? (ABG: pH 7.31, PaCO2 48, PaO2 58 on FiO2 0.6; procalcitonin 6.2 ng/mL; blood cultures negative; creatinine 1.0 mg/dL.)