Molecular epidemiology of vancomycin-resistant enterococci from 6 hospitals in New York State

Background: Vancomycin resistance among enterococci is an emerging nosocomi al problem. Consequently, it is important to understand the distribution of vancomycin-resistant enterococci (VRE) within and between hospitals to imp lement appropriate infection control measures. Methods: In this study, 116 VRE isolates obtained from patients in 6 New Yo rk State hospitals were analyzed by antibiotic susceptibility testing, puls ed-field gel electrophoresis (PFGE) fingerprinting, plasmid profile analysi s, vanA and vanB polymerase chain reaction, and DNA:DNA hybridization with vanA and vanB probes. Results: PFGE and plasmid typing generally agreed, but plasmid profiles wer e more variable. These analyses revealed that genetic heterogeneity among i solates from within each of the 6 hospitals varied considerably. Among 23 E nterococcus faecium isolates from one hospital, there were only 3 PFGE type s, and 20 isolates had the same type. However, in another hospital, each is olate was genetically distinct. Closely related strains were not found in s eparate hospitals. VRE strains with vanA genes and strains with vanB genes were found in 3 hospitals. Both plasmid and chromosomal carriage of these g enes was detected. Conclusions: PFGE typing showed that nosocomial VRE transmission had occurr ed in some hospitals. However, there was no evidence for it in others. Neit her was there evidence for intrahospital transmission or for emergence of a n endemic strain. These observations demonstrate that it is important to ev aluate genetic heterogeneity among VRE before implementation of infection c ontrol measures. PFGE is the method of choice for epidemiologic typing, but polymerase chain reaction, plasmid, and hybridization studies can provide important information concerning the presence and potential for transfer of vancomycin resistance genes.