title: Evaluation of a novel chromogenic agar medium for isolation and differentiation of vancomycin-resistant Enterococcus faecium and Enterococcus faecalis isolates.
abstract: The development of reliable and rapid methods for the identification of patients colonized with vancomycin-resistant enterococci (VRE) is central to the containment of this agent within a hospital environment. To this end, we evaluated a prototype chromogenic agar medium (VRE-BMX; bioMérieux, Marcy l'Etoile, France) used to recover VRE from clinical specimens. This medium can also identify isolated colonies as either vancomycin-resistant Enterococcus faecium or Enterococcus faecalis, based on distinct colony colors. We compared the performance of VRE-BMX with bile esculin azide agar supplemented with vancomycin (BEAV). For this study, 147 stool samples were plated on each test medium and examined after 24 and 48 h of incubation. At 24 h, the sensitivity and specificity of each medium were as follows: BEAV, 90.9% and 89.9%, respectively; VRE-BMX, 96.4% and 96.6%, respectively. The positive predictive values (PPV) of VRE-BMX and BEAV at 24 h were 89.8% and 80.7%, respectively. VRE-BMX provided the identification of 10 isolates of vancomycin-resistant E. faecalis and 4 isolates of vancomycin-resistant E. faecium that were not recovered by BEAV. Further, VRE-BMX was capable of identifying patients colonized with both E. faecium and E. faecalis, a feature useful for infection control purposes that is not a function of BEAV. In terms of the recovery of vancomycin-resistant E. faecium and E. faecalis, the sensitivity and PPV were as follows: BEAV, 75.7% and 74.6%, respectively; VRE-BMX, 95.5% and 91.3%, respectively. In this initial evaluation, we found that VRE-BMX provided improved recovery of VRE from stool specimens, with the added advantage of being able to differentiate between vancomycin-resistant E. faecalis and E. faecium. Extending the incubation period beyond 24 h did not significantly improve the recovery of VRE and resulted in decreased specificity.
authors.affiliation: Department of Pathology and Immunology, Washington University School of Medicine, St. Louis, MO 63110, USA.
authors.forename: Nathan A
authors.initials: NA
authors.lastname: Ledeboer
authors.forename: Kingshuk
authors.initials: K
authors.lastname: Das
authors.forename: Michael
authors.initials: M
authors.lastname: Eveland
authors.forename: Céline
authors.initials: C
authors.lastname: Roger-Dalbert
authors.forename: Sandrine
authors.initials: S
authors.lastname: Mailler
authors.forename: Sonia
authors.initials: S
authors.lastname: Chatellier
authors.forename: William Michael
authors.initials: WM
authors.lastname: Dunne
mesh_terms: D000362:Agar / Q000737:chemistry*; D015373:Bacterial Typing Techniques; D002863:Chromogenic Compounds / Q000737:chemistry*; D003470:Culture Media / Q000737:chemistry*; D013293:Enterococcus faecalis / Q000302:isolation & purification*; D016984:Enterococcus faecium / Q000302:isolation & purification*; D005243:Feces / Q000382:microbiology; D006801:Humans; D012680:Sensitivity and Specificity; D020713:Vancomycin Resistance
chemical_list: D002863:Chromogenic Compounds; D003470:Culture Media; D000362:Agar