Pharmacology · Antimicrobials (Cell Wall Inhibitors, Protein Synthesis Inhibitors, Fluoroquinolones)

A clinical isolate of Streptococcus pneumoniae shows high-level penicillin resistance. The molecular mechanism responsible is:

  • A Acquisition of blaZ gene encoding a broad-spectrum beta-lactamase
  • B Alteration of penicillin-binding protein PBP2b reducing penicillin affinity ✓
  • C Upregulation of AcrAB-TolC efflux pump expelling penicillin
  • D Reduced outer membrane porins preventing penicillin entry
Correct answer: B. Alteration of penicillin-binding protein PBP2b reducing penicillin affinity

Explanation

S. pneumoniae resistance to penicillin arises exclusively through altered penicillin-binding proteins (PBPs), particularly PBP2b and PBP2x, which are acquired through horizontal transfer from closely related streptococci and have reduced affinity for beta-lactams. Unlike staphylococci, pneumococci do not produce beta-lactamases. Efflux pumps and porin changes are mechanisms seen in Gram-negative bacteria; pneumococci lack an outer membrane. This mechanism necessitates higher-dose amoxicillin or switching to ceftriaxone/respiratory fluoroquinolones for high-level resistance.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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