During routine surveillance in a medical ICU, a rectal swab from an asymptomatic patient grows Enterococcus faecium with MIC for vancomycin of 256 µg/mL and MIC for teicoplanin of 0.5 µg/mL. What VRE phenotype does this represent?
- A VanB phenotype ✓
- B VanA phenotype
- C VanC phenotype
- D VanD phenotype
Correct answer: A. VanB phenotype
Explanation
VanB enterococci show high-level resistance to vancomycin (MIC ≥64 µg/mL) but remain susceptible to teicoplanin (MIC ≤0.5 µg/mL), because the VanB ligase modifies the D-Ala-D-Lac terminus but the van operon is not induced by teicoplanin. VanA shows high-level resistance to both vancomycin and teicoplanin. VanC is intrinsic low-level resistance seen only in E. gallinarum and E. casseliflavus.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
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