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[MICRO-03] Antimicrobial Resistance (AMR) Mechanisms, ESBL, MRSA, NDM-1 & Stewardship
MICRO-03 • 7. MicrobiologyLearning Objectives
Classify the 4 biochemical mechanisms of bacterial resistance (Enzymatic inactivation, Target modification, Efflux pumps, Porin loss) and horizontal gene transfer (Conjugation, Transduction, Transformation).; Differentiate Ambler Classes A, B, C, and D β-lactamases (ESBL, AmpC, KPC, NDM-1 metallo-β-lactamase, OXA-48).; Apply the WHO AWaRe (Access, Watch, Reserve) framework and ICMR Hospital Antibiogram stewardship.
Chapter Overview & Core Explanation
Antimicrobial resistance happens when bacteria evolve defences—such as enzymes that chew up β-lactam rings, altered target proteins that antibiotics can no longer grip, or molecular pumps that spit the drug back out—passed rapidly between bacteria on mobile DNA plasmids.
Key Exam & Clinical Takeaways
- Vancomycin resistance in Enterococci (*vanA*) results from replacing the terminal D-Alanine-D-Alanine dipeptide with D-Alanine-D-Lactate, eliminating a critical hydrogen bond.
- Ambler Class B Metallo-β-lactamases (such as NDM-1) require Zinc (Zn2+) ions for catalysis and are inhibited by metal chelators (EDTA) in lab phenotypic testing, not by clavulanic acid or tazobactam.