Figure 6.

Alterations in bactericidal activity of vancomycin against laboratory mutants and clinical strains. (a) Against laboratory mutant WS2, vancomycin was only bactericidal (3 log reduction) at 1024 mg/L, but was bactericidal against clinical strains (MT1470 and 491858) at 64 mg/L. (b) Laboratory mutants WS2 and WS4 were less autolytic than their isogenic parent R20291. The reduced autolysis of WS2 and WS4 could contribute to tolerance to vancomycin. The MIC for WS2 is 8 mg/L and the MBC for WS2 is ∼1024 mg/L, while the lesser autolytic strain WS4 has an MIC of 16 mg/L and an MBC of >1024 mg/L.