According to the Ambler structural classification of beta-lactamases, which class consists of metallo-enzymes that require zinc at their active site and are inhibited by chelating agents such as EDTA?
- A Class B ✓
- B Class A
- C Class C
- D Class D
Correct answer: A. Class B
Explanation
The Ambler scheme divides beta-lactamases into four molecular classes based on the active site residue. Class A enzymes are zinc-dependent metallo-beta-lactamases (NDM, VIM, IMP) whose activity is abolished by chelators such as EDTA, which is the basis of the EDTA-disc synergy and eCIM tests. Classes B (KPC, TEM, SHV), C (AmpC) and D (OXA-type) all use an active-site serine instead. Class C is the tempting distractor because AmpC is clinically important, yet it remains a serine enzyme unaffected by EDTA.
Reference: Ananthanarayan and Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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