Intracellular activity of vancomycin and Ly333328, a new semisynthetic glycopeptide, against methicillin-resistant Staphylococcus aureus.

The activity of vancomycin and Ly333328, a new semisynthetic glycopeptide, against eight strains of Staphylococcus aureus showing various susceptibilities to methicillin and ciprofloxacin was examined using a colony count method. We compared the growth of strains ingested by polymorphonuclear leucocytes and non-ingested strains. MICs of vancomycin and Ly333328 against staphylococci resistant and susceptible to methicillin were 2 mg/l and 2-4 mg/l, respectively. Against all the tested extracellular staphylococci, vancomycin had only bacteriostatic activity, whereas Ly333328 showed cidal activity at 10 MIC. Against ingested staphylococci, vancomycin had nearly no activity compared with the controls, regardless of the concentration of the drug. Ly333328 at concentrations of 1 MIC and above was highly active against ingested staphylococci regardless of their susceptibility pattern. The results suggest that Ly333328 in contrast to vancomycin is active against intracellular S. aureus.