A blood culture isolate of Klebsiella pneumoniae shows an imipenem MIC of 4 µg/mL and a meropenem MIC of 8 µg/mL by E-test. The Modified Carbapenem Inactivation Method (mCIM) test is positive. The most likely resistance mechanism is:
- A Loss of outer membrane porin OmpK36 combined with hyperproduction of AmpC
- B Metallo-beta-lactamase (NDM-1 or VIM) production
- C Klebsiella pneumoniae carbapenemase (KPC) production ✓
- D ESBL production alone
Explanation
The mCIM test (a phenotypic screen where organisms are incubated with imipenem disc; carbapenemase activity degrades imipenem allowing indicator organism to grow in an inhibition zone) detects carbapenemase activity. KPC (Klebsiella pneumoniae carbapenemase) is the most prevalent serine carbapenemase globally in K. pneumoniae, conferring resistance to all carbapenems. KPC is detected by mCIM and confirmed by the CarbaNP test or immunochromatographic lateral flow assay. NDM (metallo-beta-lactamase) would show the same mCIM result but is distinguished by EDTA inhibition (eCIM) or specific lateral flow tests. Porin loss + AmpC causes only borderline carbapenem MIC elevation and is mCIM-negative.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.