Comparative Study of Selective Chromogenic (chromID VRE) and Bile Esculin Agars for Isolation and Identification of vanB -Containing Vancomycin-Resistant Enterococci from Feces and Rectal Swabs

Abstract

The new chromogenic agar chromID VRE (cIDVRE; bioMérieux) was compared with bile esculin agar (BD) containing 6 mg/liter vancomycin for the detection of colonization with vanB-containing vancomycin-resistant enterococci (VRE). At 48 h of incubation, the results obtained with both media were comparable. However, cIDVRE detected significantly more VRE at 24 h (39.3% versus 21.3%, P ‫؍‬ 0.003), and its use may facilitate the timely implementation of infection control procedures.Vancomycin-resistant enterococci (VRE) are significant nosocomial pathogens, and both vanA-and vanB-containing strains of VRE may cause serious infections, including bacteremia (10, 17). In Australia, unlike the United States and Europe, vanB-containing VRE strains predominate (2, 6). The early detection of VRE may facilitate the timely implementation of infection control measures, and surveillance by examination of fecal and rectal swab specimens has been adopted as a means of reducing outbreaks caused by VRE (16). Recently, it has been reported from Europe and the United States that the use of new chromogenic agars improves the ability to detect VRE isolates from fecal and rectal swab specimens (5,11,12). ChromID VRE agar (cIDVRE; bioMérieux, Marcyl'Etoile, France), which contains 8 mg/liter vancomycin, also has the advantage of differentiating Enterococcus faecalis and Enterococcus faecium, as it detects the ␤-glucosidase and the ␤-galactosidase produced by the two species respectively (5, 11, 12; cIDVRE product insert, reference no. 43 002, 2007; bioMérieux). vanA-containing VRE typically have vancomycin MICs of Ն64 mg/liter (4, 15) and would be expected to grow well in the presence of 8 mg/liter vancomycin. However, vanBcontaining VRE strains, which may exhibit much lower vancomycin MICs, including MICs of Յ4 mg/liter (4, 8), may not be as readily isolated on cIDVRE as they are on bile esculin agar (Enterococcosel; BD, Sparks, MD) containing 6 mg/liter vancomycin (EVA). At Austin Health, where vanB-containing VRE predominate, we compared cIDVRE for the detection of vancomycin-resistant strains of E. faecalis and E. faecium with EVA for the isolation of VRE from fecal and rectal swab specimens.Feces and rectal swabs were inoculated directly onto both cIDVRE and EVA. The media were inoculated with separate cotton-tipped swab sticks for fecal specimens. As only one rectal swab specimen was collected from each patient, rectal swabs with laboratory accession numbers that were an odd number were inoculated onto cIDVRE first and then onto EVA. Inoculation of the media was in the reverse order for even-numbered specimens. The cultures were incubated at 35°C in ambient air and were examined daily, with cIDVRE incubated for 48 h, according to the manufacturer's recommendations (cIDVRE product insert; bioMérieux), and EVA plates were incubated for 72 h, as reported previously (13). Strains producing ␤-galactosidase (violet color) and ␤-glucosidase (blue-green color) on cIDVRE and esculin-positive isolates (black color) on EVA were considered possi...

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.…”

“…The reason(s) for this remain unknown and are not linked to a supposed larger reservoir of the vanB cluster in commensal intestinal colonizers (Padiglione et al, 2000), rates of which were similar in Australian, US-American and European studies (Stamper et al, 2007;Graham et al, 2008;Grabsch et al, 2008b;Bourdon et al, 2010;Werner et al, 2011c). A larger reservoir of vanB-type resistance in isolates from commercial animal farming associated with an avoparcin use is unlikely; avoparcin use was ceased in Australia in 2000 and Singapore has no significant agriculture at all thus excluding a distinct animal vanB-type VRE reservoir (see chapter 7).…”

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

“…All studies reported similar rates of recovery of both VRENFM and VRENFS from chromogenic agars to those from BEAV (1,2,(4)(5)(6)(7)10). CVRE appeared to perform better than the other chromogenic agars compared to BEAV, but a direct comparison is needed to provide the most accurate comparison.…”

“…Confirmation of VRE using this medium requires 48 to 72 h. Chromogenic agars to detect VRE demonstrate promise (1)(2)(3)(4)(5)(6)(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).…”

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

“…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.…”