Fosfomycin tromethamine is used as single-dose oral therapy for uncomplicated cystitis caused by ESBL-producing E. coli. Its mechanism of action is:
- A Inhibition of MurA, blocking the first committed step of peptidoglycan synthesis ✓
- B Inhibition of lipid carrier bactoprenol recycling
- C Competitive inhibition of alanine racemase
- D Binding of the D-Ala-D-Ala terminus of peptidoglycan precursors
Correct answer: A. Inhibition of MurA, blocking the first committed step of peptidoglycan synthesis
Explanation
Fosfomycin is a phosphonic acid analogue of phosphoenolpyruvate that covalently inactivates MurA (UDP-N-acetylglucosamine enolpyruvyl transferase), the enzyme catalyzing the first cytoplasmic step of peptidoglycan synthesis. Cycloserine inhibits alanine racemase and ligase, bacitracin blocks bactoprenol dephosphorylation, and D-Ala-D-Ala binding is the vancomycin mechanism. Because its target is unique, cross-resistance with other cell wall agents does not occur.
Reference: Katzung Basic and Clinical Pharmacology, 15th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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