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Title: Improved detection of vanB2-containing enterococcus faecium with vancomycin susceptibility by Etest using oxgall supplementation.
Austin Authors: Grabsch, Elizabeth A ;Chua, Kyra Y L ;Xie, S;Byrne, J;Ballard, Susan A;Ward, P B;Grayson, M Lindsay 
Affiliation: Microbiology
Issue Date: 23-Apr-2008
Publication information: Journal of Clinical Microbiology 2008; 46(6): 1961-4
Abstract: We have isolated a number of vanB-containing Enterococcus faecium isolates on bile esculin screening agar containing 6 mg/liter vancomycin, which on subsequent susceptibility testing using Etest have repeatedly demonstrated vancomycin MICs of <or=4 mg/liter. To investigate this genotype-phenotype incongruence of "low-MIC vancomycin-resistant enterococci" (LM-VRE), we examined the molecular characteristics of these isolates, including the presence of the vanB operon, using PCR amplification and DNA sequencing. All LM-VRE isolates contained vanB associated with the transposon Tn1549 and were polyclonal. Sequencing of the vanB ligase gene showed no differences from the prototype vanB2. In addition, we examined supplemented media to improve phenotypic detection of these isolates. Etest detection of LM-VRE improved when Mueller-Hinton agar (MHA) and brain heart infusion agar (BHIA) were supplemented with 10 g/liter oxgall (MHA-Oxg and BHIA-Oxg, respectively). We assessed the sensitivity and specificity of these media to detect vancomycin resistance using vancomycin-resistant vanB-containing E. faecium (n = 11), vancomycin-susceptible (van negative) E. faecium (n = 11), vancomycin-susceptible (van negative) E. faecalis (n = 11), and our LM-VRE (n = 23) isolates. After 48 h of incubation, both MHA-Oxg and BHIA-Oxg were 100% (34/34) sensitive and 100% (22/22) specific in the identification of vancomycin resistance. These findings suggest that supplementation of MHA or BHIA with 10 g/liter oxgall should be considered in laboratories where VRE detection protocols rely primarily on strain phenotype rather than early vanB gene detection by PCR.
DOI: 10.1128/JCM.01778-07
Journal: Journal of Clinical Microbiology
Type: Journal Article
Subjects: Animals
Anti-Bacterial Agents.pharmacology
Bacterial Proteins.genetics.metabolism
Bacteriological Techniques
Culture Media.chemistry
Enterococcus faecium.classification.drug effects.genetics.isolation & purification
Microbial Sensitivity Tests.methods
Molecular Sequence Data
Sensitivity and Specificity
Appears in Collections:Journal articles

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