Comparison of agar-based media for primary isolation of glycopeptide-resistant enterococci

Abstract

OBJECTIVE: To compare four vancomycin-containing agar media for the isolation of glycopeptide-resistant enterococci (GRE) from clinical fecal specimens: kanamycin---aesculin---azide (KAA) agar; bile---aesculin---polymixin (BAP) agar; aztreonam---amphotericin blood (CBAA) agar; and neomycin blood (CBN) agar. METHODS: Fecal specimens from 125 patients were inoculated onto each medium. Media were examined for enterococci after incubation for up to 48 h. Enterococci were identified to species level, and glycopeptide phenotypes were determined by measuring minimum inhibitory concentrations of vancomycin and teicoplanin. RESULTS: GRE were isolated from 44/125 samples. Enterococcus faecalis and Enterococcus faecium isolates, expressing glycopeptide resistance of the VanA or VanB phenotypes, were recovered from 27/33 (82%) specimens on BAP medium, 26/33 (79%) on KAA medium, and 21/33 (64%) on CBN and CBAA media. Enterococcus gallinarum and Enterococcus casseliflavus isolates expressing low-level glycopeptide resistance (VanC phenotype) were recovered from 14/15 (93%) specimens on CBAA medium, 7/15 (47%) on KAA and CBN media, and 6/15 (40%) on BAP medium. CONCLUSIONS: The media tested in this study, with the exception of CBN medium, detected at least 75% of patients colonized by GRE. Further development of BAP, CBAA and KAA media is warranted to improve growth and selectivity.

Evaluation of a New Chromogenic Medium, chromID VRE, for Detection of Vancomycin-Resistant Enterococci in Stool Samples and Rectal Swabs

“…The same sensitivity was found in our laboratory for VCA3 agar (5). The bile-esculin-based media supplemented with vancomycin had sensitivities of 80 to 100% (1,3,20).…”

“…Early detection of VRE in fecal specimens is important for nosocomial prevention measures, epidemiologic infectious disease follow-up, and also prevention of vancomycin-resistant Staphylococcus aureus emergence (10,19). Several agar and broth medium formulations containing vancomycin have been developed for this purpose (1,3,5,11,13,18,20). However, no consensus has been established for medium base, vancomycin concentration, or method of use.…”

“…The aims of this study were to assess the performance of chromID VRE medium in a low-prevalence context and to determine the best method of use. ChromID VRE was compared with a modified bile esculin agar, which is one of the best media for the isolation of VRE (3).…”

Evaluation of the Effectiveness of an Enzymatic Cleaner and Glutaraldehyde-Based Disinfectant for Chemothermal Processing of Flexible Endoscopes in Washer-Disinfectors in Accordance with prEN ISO 15 883

“…In the present study, however, all test pieces were visibly clean even after the use of glutaraldehyde, and none of the test pieces revealed any viable test organism after reprocessing, as shown by filling of the treated test pieces with KANA. KANA was chosen because it is a selective agar with a high sensitivity for detection of the test organism E. faecium [37]. Other types of agar would not have indicated the presence of residual test organisms with such a high level of sensitivity.…”