What resistance determinants are most commonly screened in enterococci for vancomycin resistance?

• A. vanC and vanD
• B. vanB and vanD
• C. vanA and vanB
• D. vanA and vanC

Answer: (C)

In enterococci, the resistance determinants most commonly screened for vancomycin resistance are vanA and vanB. These two genes drive the vast majority of clinically relevant, transferable vancomycin resistance seen in hospital isolates. They are often located on mobile elements, enabling rapid spread between strains and even species, which is why routine screening panels focus on them.

vanA generally gives high-level resistance to both vancomycin and teicoplanin, while vanB produces vancomycin resistance with variable (often teicoplanin-susceptible) profiles. By contrast, vanC is intrinsic to certain species (like E. gallinarum and E. casseliflavus) and is not typically involved in the problematic transferable resistance seen in clinical settings. vanD is much rarer and contributes far less to the resistant problem in routine surveillance.

So, for monitoring and detecting vancomycin resistance in enterococci, testing for vanA and vanB captures the most clinically significant and mobilizable resistance determinants.