An Enterococcus gallinarum isolate recovered from a urinary tract infection shows a vancomycin MIC of 16 mg/L but is fully susceptible to teicoplanin. This phenotype results from:
- A The vanA operon encoding a D-Ala:D-Lac ligase
- B Reduced permeability of the cell envelope to glycopeptides
- C The intrinsic vanC gene encoding a D-Ala:D-Ser ligase that alters the peptidoglycan terminus ✓
- D Overproduction of penicillin-binding proteins competing for the drug
Explanation
Enterococcus gallinarum and E. casseliflavus carry the chromosomal, non-transferable vanC gene cluster, whose ligase substitutes D-serine for D-alanine at the peptidoglycan terminus, lowering glycopeptide affinity modestly and producing low-level vancomycin resistance (MIC 8 to 32 mg/L) with retained teicoplanin susceptibility. The acquired vanA operon produces much higher MICs and teicoplanin resistance, so option A fits E. faecium rather than this organism. Glycolytic permeability changes and PBP overproduction are not mechanisms of enterococcal glycopeptide resistance.
Reference: Koneman's Color Atlas and Textbook of Diagnostic Microbiology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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