Rapid characterization schemes for surveillance isolates of vancomycin-resistant enterococci

Surveillance cultures for vancomycin-resistant enterococci (VRE) and subsequent characterization of the isolates can be extremely burdensome and difficult. Therefore, efficient and reliable schemes for the characterization of surveillance isolates are needed. In this study, a commercial agar (bile esculin azide agar with 6 microg of vancomycin per ml BEAA; Remel, Lenexa, Kans.) was used in the initial screening step to establish relatively rapid (i.e., in 6 mm, while only one VanC strain produced a zone of < 15 mm. Challenging this phenotypic scheme with 47 stock VRE isolates produced similar findings. In direct PCR analyses, false-negative vanA and vanB results occurred with 12% of the specimens. Many of the false-negative reactions also failed to produce an internal control product, which underscores the need for including control primers when a PCR scheme is used. In summary, the phenotype- and the PCR-based schemes provide efficient methods for characterizing VRE within 24 h of isolation.