Evaluation of BBL CHROMagar VanRE for Detection of Vancomycin-Resistant Enterococci in Rectal Swab Specimens

Abstract

A study was performed on 517 surveillance rectal swabs to evaluate a selective and differential chromogenic medium, the BBL CHROMagar VanRE (CVRE), which enables recovery and identification of VanA-and VanB-containing Enterococcus faecium (ENFM) and Enterococcus faecalis (ENFS) isolates. Compared to BBL Enterococcosel agar, a bile-esculin-azide-vancomycin (BEAV) agar, the initial overall sensitivity, specificity, and positive and negative predictive values of CVRE for the detection of vancomycin-resistant ENFM and ENFS were 99.1% and 94.8% and 84.2% and 99.7%, respectively. Among our patient population, more vancomycin-resistant enterococci (VRE) were recovered with CVRE than BEAV.Vancomycin-resistant enterococci (VRE) are major causes of nosocomial infections in health care facilities, and those patients infected with VRE have worse outcomes while hospitalized (8). Rapid, reliable identification of these antibioticresistant organisms is crucial for patient management and infection control measures (9, 12).Culture from rectal swabs or stool specimens onto bileesculin-azide agar with vancomycin (BEAV) is the VRE screening method used in many clinical laboratories. Confirmation of VRE using this medium requires 48 to 72 h. Chromogenic agars to detect VRE demonstrate promise (1-7, 10). BBL CHROMagar VanRE (CVRE; BD Diagnostics, Sparks, MD) is a selective and differential chromogenic agar under development for the detection of vancomycin-resistant E. faecium (VRENFM) and vancomycin-resistant Enterococcus faecalis (VRENFS). CVRE contains 8 g/ml of vancomycin and uses chromogenic substrates to phenotypically differentiate VRENFM as mauve colonies and VRENFS as green colonies. Other bacteria are inhibited or typically grow as a color other than mauve or green. Our study compared the clinical performance of CVRE with that of BEAV for primary isolation and detection of VRE from surveillance rectal swabs.Patient samples. This industry-sponsored clinical trial was approved by the Johns Hopkins University School of Medicine Institutional Review Board. At the Johns Hopkins Hospital, VRE surveillance cultures are obtained weekly from patients in all intensive care units (ICUs) and from other high-risk groups, such as oncology, transplant, and HIV patients. Multiple specimens per patient were permitted in the study if previous cultures were negative. Two positive specimens were admissible, provided the specimens were collected Ͼ5 days apart.Surveillance rectal swabs were first inoculated onto BEAV followed by inoculation onto CVRE. Both plates were aseptically streaked for isolation and incubated at 37°C for 24 to 48 h. BEAV. BEAV plates with 6 g/ml of vancomycin were incubated aerobically. No-growth cultures or those not consistent with VRE by 48 h had no further workup. Presumptive colonies for VRE (black colonies with a Gram stain of positive cocci) were isolated to 5% sheep blood agar (SBA) and incubated for an additional 18 to 24 h. L-Pyrrolidonyl-␤-naphthylamide enzyme (PYR)-positive colonies were identified with the BD ...

Comparison of Medium, Temperature, and Length of Incubation for Detection of Vancomycin-Resistant Enterococcus

“…All specimens that were discrepant between the 24-h and 48-h plates were those in which there were Ͻ10 CFU/plate. Therefore, similar to previous reports, there was no significant difference in overall results when incubation was extended to 48 h beyond the initial 24 h of incubation (4,5,6,10).…”

“…The most common specimens to screen for colonization with VRE are rectal swabs or stool specimens. Several selective and differential media have been developed and evaluated specifically for the purpose of screening for VRE (2)(3)(4)(5)(6)(7)(8)10). Campylobacter (Campy) agar, which supports the growth of VRE and contains 10 g/ml vancomycin, is readily available in most clinical laboratories due to its use in the plating of routine stool cultures to isolate Campylobacter jejuni.…”

Current Trends of Emergence and Spread of Vancomycin-Resistant Enterococci

“…Preliminary findings direct to a similar trend in other European countries like Sweden (Soderblom et al, 2010;Fang et al, 2010). If this increased VanB-type prevalence is linked to a supposed reservoir of vanB among enterococcal or non-enterococcal intestinal colonizers (Stamper et al, 2007;Young et al, 2007;Graham et al, 2008;Usacheva et al, 2010;Bourdon et al, 2010;Werner et al, 2011c) or simply linked to an improved and better identification of low-level expressed VanB-type resistance (Pendle et al, 2008;Grabsch et al, 2008a;Grabsch et al, 2008b;Stamper et al, 2010) in relation to a reduced breakpoint as defined by EUCAST (EUCAST Clinical Breakpoint Table v. 1.1 2010-04-27) 6 remains to be elucidated in further studies.…”

Comparison of direct cultivation on a selective solid medium, polymerase chain reaction from an enrichment broth, and the BD GeneOhm™ VanR Assay for identification of vancomycin-resistant enterococci in screening specimens

“…Therefore, early recognition and isolation of VRE colonized patients are critical steps in reducing VRE infections and terminating VRE outbreaks ( [Aumeran et al, 2008] and [Deplano et al, 2007]). Various commercial phenotypic and genotypic assays are available for VRE screening differing in sensitivity and specificity ( [Bourdon et al, 2010], , [Ledeboer et al, 2007], [Stamper et al, 2007], [Stamper et al, 2010] and [Young et al, 2007]). In general, genotypic assays may be advantageous over phenotypic tests being much faster and capable of circumventing problems associated with a sometimes low expression of vanA-and vanB-type resistance phenotypes ( [Naas et al, 2005], [Stamper et al, 2007] and [Song et al, 2008]).…”