DECREASED SUSCEPTIBILITIES TO TEICOPLANIN AND VANCOMYCIN AMONG COAGULASE-NEGATIVE METHICILLIN-RESISTANT CLINICAL ISOLATES OF STAPHYLOCOCCI

Of 41 methicillin-resistant coagulase-negative staphylococcal clinical isolates collected during a 5-month period between late 1995 and earl y 1996, 28 showed tube dilution teicoplanin MICs of 4 to 8 mu g/ml whi ch increased to 16 to 32 mu g/ml upon prolonged incubation, Cultures o f such bacteria were heterogeneous; they contained subpopulations with frequencies of 10(-5) to 10(-4) that could grow on up to 50 mu g of t eicoplanin per mi, The same cultures were also heterogeneous with resp ect to susceptibility to vancomycin; while the MICs for the majority o f cells were 2 to 4 mu g/ml, subpopulations that could grow on 6 to 12 mu g of vancomycin per mi were also present at frequencies of 10(-5) to 10(-7). Selective enrichment of such cultures for the resistant sub population occurred with relative ease under laboratory conditions, He terogeneous phenotypes for teicoplanin (but not for vancomycin) suscep tibility were also identified in several Staphylococcus epidermidis is olates collected during the preantibiotic era, The addition of half th e MIC of teicoplanin inhibited autolysis and caused formation of cellu lar aggregates which disintegrated to individual bacteria in the stati onary phase when the titer of teicoplanin in the medium fell to undete ctable levels, indicating removal of the antibiotic from the culture m edium by the bacteria.