Molecular epidemiology and antibiotic susceptibility of enterococci in Cincinnati, Ohio: a prospective citywide survey

Abstract

To determine patterns of antimicrobial susceptibility among enterococci and to assess molecular characteristics of vancomycin-resistant enterococci, 157 clinical blood isolates of enterococci from 10 hospitals in Cincinnati, Ohio, were prospectively collected during a 6-month period from February to July 1995. The isolates included 108 (69%) E. faecalis isolates, 46 (29%) E. faecium isolates, and 1 isolate each of E. avium, E. durans, and E. gallinarum. The E. faecalis and E. faecium isolates differed in their susceptibilities to ampicillin (100 versus 20%), ampicillin-sulbactam (100 versus 13%), vancomycin (100 versus 57%), imipenem (94 versus 2%), and high levels of gentamicin (59 versus 83%). Supplemental susceptibility testing of the 21 vancomycin-resistant isolates showed that 21 (100%) were susceptible to chloramphenicol and that only 7 (33%) were susceptible to doxycycline. Nineteen (90%) of the vancomycin-resistant E. faecium isolates were of the VanB phenotype, with vanB resistance genes detected by PCR and hybridization with gene-specific probes; and the E. gallinarum isolates demonstrated the VanC phenotype with the vanC1 gene. One vancomycin-resistant E. faecium isolate was highly resistant to both teicoplanin and vancomycin, corresponding to the VanA phenotype; however, it was found to have the vanB gene. Pulsed-field gel electrophoresis (PFGE) revealed that all of the 19 E. faecium isolates with the VanB phenotype had identical to closely related banding patterns. Hybridization of restriction enzyme-digested DNA separated by PFGE with a vanB gene probe demonstrated differences in the locations of vanB genes that corresponded closely to the PFGE banding patterns. Our study has documented that the emerging vancomycin resistance in our city was mainly due to the clonal dissemination of a single strain of E. faecium VanB.