In PCR testing for suspected vancomycin-resistant enterococci (VRE), which gene would you attempt to identify for Enterococcus faecium or Enterococcus faecalis?

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The main idea is that vancomycin resistance in Enterococcus faecium and Enterococcus faecalis is usually due to acquired van genes, specifically vanA or vanB, which are the ones PCR tests are designed to detect to confirm VRE. These genes are carried on mobile elements and confer high-level resistance, making them the diagnostic targets when you suspect VRE in these species.

VanC, on the other hand, is an intrinsic, chromosomal resistance mechanism found in other Enterococcus species like E. gallinarum and E. casseliflavus. It tends to give a lower level or intrinsic resistance and is not the transferable resistance that defines VRE in faecium or faecalis. So testing for VanC in faecium/faecalis wouldn’t explain the common VRE scenario and wouldn’t be the primary diagnostic target.

The mecA gene is associated with methicillin resistance in staphylococci, not vancomycin resistance in Enterococcus, so it isn’t relevant for identifying VRE in these species.