A blood culture isolate of Enterococcus faecium shows a vancomycin MIC of 128 mg/L and teicoplanin MIC of 256 mg/L. The van gene responsible encodes a ligase that produces D-Ala-D-Lac instead of D-Ala-D-Ala. This is consistent with:
- A VanB phenotype
- B VanC phenotype
- C VanA phenotype ✓
- D VanD phenotype
Correct answer: C. VanA phenotype
Explanation
VanA is the most clinically significant vancomycin resistance phenotype, conferring high-level resistance to both vancomycin (MIC ≥64 mg/L) and teicoplanin (MIC ≥16 mg/L). It involves the VanA ligase, which substitutes D-Lac for D-Ala at the terminus, reducing glycopeptide binding 1000-fold. VanB confers resistance to vancomycin but not teicoplanin; VanC is intrinsic and low-level in E. gallinarum; VanD is rare with intermediate-level resistance.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.