Evaluation of chromogenic media for the isolation of vancomycin-resistant enterococci from stool samples

This study sought to evaluate the performance of two chromogenic media designed for the isolation of vancomycin-resistant enterococci (VRE) and compare them with a traditional bile-esculin medium for the isolation of VRE from stool samples. A total of 285 stool samples were inoculated onto Chromogenic VRE Agar (AES VRE agar; AES Chemunex), chromID VRE (bioMErieux) and VRE Agar (Oxoid) both directly and also following broth enrichment. In total 18 strains of vancomycin-resistant Enterococcus faecium were recovered, including 17 harbouring the vanA gene and one with vanB. On direct culture, the sensitivity of the three media was 66.7%, 77.8% and 44.4% and after broth enrichment 66.7%, 83.3% and 77.8% using AES VRE Agar, chromID VRE and Oxoid VRE Agar respectively. All three media are useful tools for the isolation of VRE from stool samples. AES VRE Agar and bioMErieux chromID VRE are easier to use than Oxoid VRE Agar due to diffusion of black coloration from the latter. This is the first study to evaluate the performance of AES VRE Agar and the first to compare two media containing synthetic chromogens for the isolation of VRE.