A hospital has an outbreak of carbapenem-resistant Klebsiella pneumoniae (CRKP). The organism produces NDM-1 (New Delhi Metallo-beta-lactamase). Metallo-beta-lactamases like NDM-1 are inhibited by which agent used in clinical susceptibility testing to detect MBL production?
- A EDTA (ethylenediaminetetraacetic acid) ✓
- B Clavulanic acid
- C Tazobactam
- D Sulbactam
Correct answer: A. EDTA (ethylenediaminetetraacetic acid)
Explanation
NDM-1 and other metallo-beta-lactamases (MBLs: NDM, VIM, IMP) require zinc ions as cofactors for enzymatic activity. EDTA chelates zinc (and other divalent cations), inhibiting MBL activity. Combined disc/synergy tests use EDTA with imipenem: an increased zone of inhibition with EDTA compared to imipenem alone (synergy) confirms MBL production. Clavulanic acid, tazobactam, and sulbactam inhibit serine beta-lactamases (ESBL, Class A KPC) but do NOT inhibit MBLs. This is a key diagnostic distinction.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.