Heterogeneous expression of glycopeptide resistance in enterococci associated with transfer of vanB.

In mating experiments using a clinical strain that constitutively expresses vanB-encoded glycopeptide resistance, resistance transfer was detectable at a frequency of <10(-7) transconjugants/donor. Vancomycin MICs for transconjugants were 2- to 10-fold lower than those for the donor; both inducibly and constitutively resistant transconjugants were obtained. These findings demonstrate that the transfer of vanB among enterococci can be associated with substantial alterations in the level and control of glycopeptide resistance expression.