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.
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™ VRE Agar, CHROMagar™ VRE, and chromID™ 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.
National Reference Centre for Staphylococci and Enterococci, Division Nosocomial Infections, Department of Infectious Diseases, Robert Koch-Institut, Wernigerode Branch, Germany.
Ingo
I
Klare
Carola
C
Fleige
Uta
U
Geringer
Wolfgang
W
Witte
Guido
G
Werner
D000362:Agar; D001426:Bacterial Proteins / Q000235:genetics; D002863:Chromogenic Compounds / Q000378:metabolism*; D003470:Culture Media / Q000737:chemistry*; D016984:Enterococcus faecium / Q000187:drug effects* / Q000235:genetics / Q000254:growth & development / Q000302:isolation & purification*; D005060:Europe; D005838:Genotype; D016908:Gram-Positive Bacterial Infections / Q000175:diagnosis*; D006801:Humans; D008403:Mass Screening / Q000379:methods*; D008826:Microbial Sensitivity Tests / Q000379:methods; D012680:Sensitivity and Specificity; D020713:Vancomycin Resistance
D001426:Bacterial Proteins; D002863:Chromogenic Compounds; D003470:Culture Media; C079913:VanB protein, Enterococcus; D000362:Agar