The vanB Gene Confers Various Levels of Self-Transferable Resistance to Vancomycin in Enterococci

Thirty-nine strains of Enterococcus faecium and Enterococcus faecalis resistant to vancomycin and susceptible to teicoplanin on disk susceptibility testing (phenotypic class B) were isolated in 15 hospitals in Europe and the United States. The MICs of vancomycin for these strains ranged from 4 to 1024 micrograms/mL. Part of the vancomycin resistance gene vanB from E. faecalis V583 hybridized with a single but variably sized HindIII-KpnI fragment of total DNA from all 39 strains. This indicates that a single class of resistance determinants accounts for the VanB phenotype. No hybridization was detected with DNA from intrinsically resistant Enterococcus gallinarum or Enterococcus casseliflavus. Hybridization with DNA from enterococcal strains susceptible to or with acquired resistance to vancomycin and teicoplanin was not observed. The genes conferring resistance to vancomycin were self-transferable to other Enterococcus strains in 14 of the 39 strains. It thus appears that vanB confers various levels of conjugative vancomycin resistance in enterococci.