A patient with community-acquired atypical pneumonia was started on amoxicillin-clavulanate and showed no clinical improvement. Culture of respiratory secretions later grew Mycoplasma pneumoniae. The fundamental reason for the failure of amoxicillin-clavulanate in this infection is:

• A The organism produces extended-spectrum beta-lactamases
• B The organism resides intracellularly where beta-lactams cannot penetrate
• C The organism lacks a peptidoglycan cell wall, the target of beta-lactams ✓
• D The organism alters its ribosomal RNA to reduce drug binding

Explanation

Mycoplasmas are the smallest free-living bacteria and uniquely lack a cell wall; their cytoplasmic membrane contains cholesterol, which they must obtain from the host or medium. Because beta-lactams act on penicillin-binding proteins involved in peptidoglycan cross-linking, they have no target in mycoplasmas. Effective agents are those inhibiting protein synthesis or DNA replication, namely macrolides, tetracyclines and fluoroquinolones. Ribosomal alteration describes macrolide resistance mechanisms, not beta-lactam failure.

Reference: Jawetz, Melnick & Adelberg's Medical Microbiology, 28th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.