Prospective, Multicenter Evaluation of the BD GeneOhm VanR Assay for Direct, Rapid Detection of Vancomycin-Resistant Enterococcus Species in Perianal and Rectal Specimens

Abstract

The BD GeneOhm VanR assay (BD Diagnostics, San Diego, CA), a qualitative test for the rapid detection of vancomycin-resistant enterococci (VRE) from rectal and/or perianal swabs, combines integrated nucleic acid extraction and automated polymerase chain reaction for the detection of vanA and/or vanB gene sequences. We studied 1,027 perianal and rectal swab specimens from 3 geographically distinct US sites (prevalence rates, 13.1%-25.8%). Direct swab specimens were tested by the assay and compared with direct culture. The sensitivity, specificity, and positive and negative predictive values of the assay were 93.2%, 81.9%, 54.4%, and 98.1%, respectively. The specificity was limited largely due to false-positives in the vanB portion of the assay. Specificity with perianal swabs was significantly greater than with rectal swabs, 87.1% vs 74.7%, respectively (P < .0001). When used only to detect resistance conferred by vanA, the assay was 88.3% (158/179) sensitive and 95.8% (802/837) specific, with positive and negative predictive values of 81.9% and 97.4%, respectively. The assay is a simple, rapid, and acceptable method for screening for VRE in a variety of populations in which vanA is the predominant genotype. Samples positive for the vanB genotype should be confirmed by culture owing to the apparent high number of false-positive results.

Performance of three chromogenic VRE screening agars, two Etest® vancomycin protocols, and different microdilution methods in detecting vanB genotype Enterococcus faecium with varying vancomycin MICs

“…The problem of low-level vancomycin resistance expression in vanB type enterococci has been known for a long time but has not been extensively studied or addressed until now, most probably due to its supposed low prevalence and thus moderate clinical significance ( Adler et al, 2010, Raponi et al, 2010and Rathe et al, 2010. The low predictive value for vanB VRE according to the results of VRE screening studies performed in countries of different continents was mainly addressed to the wide prevalence of vanB genes in nonenterococcal, intestinal colonizers ( Rathe et al, 2010, Stamper et al, 2007, Usacheva et al, 2010and Young et al, 2007. It has to be considered that a substantial number of vanB enterococci may have been missed in previous studies comparing the performance of real-time PCR-based screening assays against phenotypic comparator assays with a supposed low sensitivity in diagnosing vanB VRE with low-level vancomycin resistance expression (Werner et al, 2011b).…”

“…Detection of vanB type resistance by molecular methods circumvents the complications mentioned above with respect to a phenotypical measurement of resistance gene expression but conflicts with prevalence of vanB among nonenterococcal, intestinal colonizers ( Ballard et al, 2005, Domingo et al, 2005and Graham et al, 2008. The vanB gene prevalence in nonenterococcal, intestinal colonizers did not show a geographical preference and appeared at similar rates in different parts of the world as deduced from a number of clinical studies using real-time polymerase chain reaction (PCR)-based screening assays (Bourdon et al, 2010, Stamper et al, 2007, Usacheva et al, 2010, Werner et al, 2011band Young et al, 2007.…”

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

“…In another study, Usacheva et al (2010) compared the results of the BD GeneOhm™ VanR Assay with phenotypical tests only. Therefore their results may be biased by VRE with low MICs and are not comparable to our results.…”

“…This has led to increased interest in screening of patients for colonization as well as to increased interest in methods used for a fast, sensitive, and reliable VRE detection (Vonberg et al, 2007). Rapid screening methods for VRE using direct polymerase chain reaction (PCR) from rectal swabs or stool have been described ( [Palladino et al, 2003], [Petrich et al, 1999] and [Satake et al, 1997]); some of these assays are commercially available ( [Bourdon et al, 2010], [Stamper et al, 2007], [Sloan et al, 2004] and [Usacheva et al, 2010]). These tests have been evaluated in a few studies performed, and excellent sensitivity and specificity for detecting vanA enterococci were shown, and a low specificity due to comparably high rates of supposed false-positive vanB samples appeared as a problem ( [Stamper et al, 2007] and [Sloan et al, 2004]).…”

Current Trends of Emergence and Spread of Vancomycin-Resistant Enterococci

“…Molecular assays provide certain advantages over microbiological tests in terms of time, sensitivity and accuracy. Prevalence of van genes, especially vanB in intestinal, nonenterococcal species impairs performance of rapid, molecular screening assays targeting the corresponding resistance genes only (Stamper et al, 2007;Mak et al, 2009;Usacheva et al, 2010). Results of a number of studies performed with various commercially available diagnostic assays in Northern America, Australia, Asia and different countries in Europe also revealed that vanB is generally prevalent among human intestinal colonizers and that this is not a specific property of human intestinal colonisers in certain parts of the world …”