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

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• 作者：Ingo Klare ; Carola Fleige ; Uta Geringer ; Wolfgang Witte ; Guido Werner
• 关键词：VRE ; Antibiotic susceptibility testing ; Vancomycin heteroresistance
• 刊名：Diagnostic Microbiology and Infectious Disease
• 出版年：2012
• 出版时间：October, 2012
• 年：2012
• 卷：74
• 期：2
• 页码：171-176
• 全文大小：409 K

文摘

Frequencies of vanB-type Enterococcus faecium increased in Europe during the last years. VanB enterococci show various levels of vancomycin MICs even below the susceptible breakpoint challenging a reliable diagnostics. The performance of 3 chromogenic vancomycin-resistant enterococci (VRE) screening agars, 2 Etest? vancomycin protocols, and different microdilution methods to detect 129 clinical vanB E. faecium strains was investigated. Altogether, 112 (87 % ) were correctly identified as VanB-type Enterococcus by microdilution MICs. An Etest? macromethod protocol was more sensitive than the standard protocol while keeping sufficient specificity in identifying 15 vanA/vanB-negative strains. Three chromogenic VRE agars performed similarly with 121 (94 % ), 123 (95 % ), and 124 (96 % ) vanB isolates that grew on Brilliance^TM VRE Agar, CHROMagar^TM VRE, and chromID^TM VRE agar, respectively. Using identical media and conditions, we did not identify different growth behaviour on agar and in broth. A few vanB strains showed growth of microcolonies inside the Etest? vancomycin inhibition zones, suggesting a VanB heteroresistance phenotype.