A patient with hospital-acquired pneumonia grows Klebsiella pneumoniae on culture. Disk diffusion shows reduced zone to cefotaxime and ceftazidime; adding clavulanic acid to ceftazidime disk restores the zone (zone enhancement ≥5 mm). MIC of meropenem is 0.25 μg/mL. The most appropriate antibiotic is:
- A Piperacillin-tazobactam monotherapy
- B Cefepime alone
- C Meropenem (carbapenem) ✓
- D Colistin
Correct answer: C. Meropenem (carbapenem)
Explanation
Zone enhancement with clavulanic acid confirms ESBL (extended-spectrum beta-lactamase) production; ESBLs hydrolyze all third-generation cephalosporins and aztreonam. Carbapenems (meropenem MIC 0.25 μg/mL, well below susceptibility breakpoint) remain the treatment of choice for serious ESBL infections. Piperacillin-tazobactam is unreliable for severe ESBL infections (inoculum effect). Cefepime is hydrolyzed by many ESBLs. Colistin is reserved for carbapenem-resistant organisms.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.