A carbapenem-resistant Klebsiella pneumoniae (CRKP) isolate grows on blood agar. Modified carbapenem inactivation method (mCIM) is positive; EDTA mCIM (eCIM) is also positive. This pattern (both mCIM positive and eCIM positive) is most consistent with:

• A KPC (serine carbapenemase); inhibited by avibactam
• B MBL (metallo-beta-lactamase, e.g., NDM-1 or VIM); inhibited by EDTA ✓
• C OXA-48 class D carbapenemase; partially inhibited by EDTA
• D AmpC combined with porin loss; no true carbapenemase present

Explanation

The modified carbapenem inactivation method (mCIM) detects all carbapenemases. The EDTA-enhanced mCIM (eCIM) distinguishes metallo-beta-lactamases (MBLs, e.g., NDM-1, VIM, IMP) from serine carbapenemases: MBLs use a zinc ion for catalysis and are inhibited by EDTA (zinc chelator), causing a positive eCIM result. KPC and OXA-48 are serine carbapenemases; EDTA does not inhibit them (eCIM negative, mCIM positive only). NDM-1 (New Delhi metallo-beta-lactamase) is the predominant MBL in India. Treatment options for NDM-1 producers are very limited: ceftazidime-avibactam + aztreonam, or colistin + fosfomycin.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.