Vancomycin-resistant <it>vanB</it>-type <it>Enterococcus faecium</it> isolates expressing varying levels of vancomycin resistance and being highly prevalent among neonatal patients in a single ICU

• Main Authors: Werner Guido, Klare Ingo, Fleige Carola, Geringer Uta, Witte Wolfgang, Just Heinz-Michael, Ziegler Renate
• Format: Article
• Language: English
• Published: BMC 2012-05-01
• Series: Antimicrobial Resistance and Infection Control
• Online Access: http://www.aricjournal.com/content/1/1/21

<p>Abstract</p> <p>Background</p> <p>Vancomycin-resistant isolates of <it>E. faecalis</it> and <it>E. faecium</it> are of special concern and patients at risk of acquiring a VRE colonization/infection include also intensively-cared neonates. We describe here an ongoing high prevalence of VanB type <it>E. faecium</it> in a neonatal ICU hardly to identify by routine diagnostics.</p> <p>Methods</p> <p>During a 10 months’ key period 71 <it>E. faecium</it> isolates including 67 <it>vanB</it>-type isolates from 61 patients were collected non-selectively. Vancomycin resistance was determined by different MIC methods (broth microdilution, Vitek® 2) including two Etest® protocols (McFarland 0.5/2.0. on Mueller-Hinton/Brain Heart Infusion agars). Performance of three chromogenic VRE agars to identify the <it>vanB</it> type outbreak VRE was evaluated (Brilliance^TM VRE agar, chromID^TM VRE agar, CHROMagar^TM VRE). Isolates were genotyped by <it>Sma</it>I- and <it>Ceu</it>I-macrorestriction analysis in PFGE, plasmid profiling, <it>vanB</it> Southern hybridisations as well as MLST typing.</p> <p>Results</p> <p>Majority of <it>vanB</it> isolates (n = 56, 79%) belonged to a single ST192 outbreak strain type showing an identical PFGE pattern and analyzed representative isolates revealed a chromosomal localization of a <it>vanB2</it>-Tn<it>5382</it> cluster type. Vancomycin MICs in cation-adjusted MH broth revealed a susceptible value of ≤4 mg/L for 31 (55%) of the 56 outbreak VRE isolates. Etest® vancomycin on MH and BHI agars revealed only two <it>vanB</it> VRE isolates with a susceptible result; in general Etest® MIC results were about 1 to 2 doubling dilutions higher than MICs assessed in broth and values after the 48 h readout were 0.5 to 1 doubling dilutions higher for <it>vanB</it> VRE. Of all <it>vanB</it> type VRE only three, three and two isolates did not grow on Brilliance^TM VRE agar, chromID^TM VRE agar and CHROMagar^TM VRE, respectively. Permanent cross contamination via the patients’ surrounding appeared as a possible risk factor for permanent VRE colonization/infection.</p> <p>Conclusions</p> <p>Low level expression of <it>vanB</it> resistance may complicate a proper routine diagnostics of <it>vanB</it> VRE and mask an ongoing high VRE prevalence. A high inoculum and growth on rich solid media showed the highest sensitivity in identifying <it>vanB</it> type resistance.</p>