A Pseudomonas aeruginosa isolate from a ventilator-associated pneumonia shows high-level resistance to imipenem while meropenem susceptibility is retained. No carbapenemase is detected by phenotypic testing. The single most likely mechanism is:
- A Loss or alteration of the OprD porin ✓
- B Plasmid-mediated qnr determinants
- C Overexpression of the MexXY efflux pump
- D Alteration of DNA gyrase grlA region
Correct answer: A. Loss or alteration of the OprD porin
Explanation
Imipenem enters Pseudomonas aeruginosa chiefly through the OprD (OccD1) channel; loss or structural alteration of OprD produces selective imipenem resistance with little effect on meropenem, which uses alternative routes. This is the classic non-enzymatic carbapenem resistance mechanism in this species. Efflux pumps such as MexAB-OprM contribute modestly to carbapenem resistance but do not produce the selective imipenem-only phenotype, and gyrase changes confer fluoroquinolone resistance, not beta-lactam resistance.
Reference: Ananthanarayan and Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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