VANCOMYCIN TOLERANCE IN STAPHYLOCOCCUS AUREUS ISOLATED DURING TREATMENT OF CAPD PERITONITIS

The susceptibility to vancomycin of nine staphylococcal strains responsible for nine episodes of peritonitis in patients on continuous ambulatory peritoneal dialysis was correlated with outcome of therapy. All strains examined had MIC values indicating sensitivity (MIC .:; 4 μg/ml). Tolerance was observed in one strain of Staphylococcus aureus (MIC = 1 μg/ml., MBC = 64 μg/ml). Time-kill studies using three different media demonstrated this organism's reduced susceptibility to vancomycin and suggested that testmedium composition may also affect the result. The patient with the tolerant strain, required an extended period of treatment. A bacterium is said to exhibit tolerance when the ratio between the minimum bactericidal concentration (MBC) and minimum inhibitory concentration (MIC) is 32 or greater (9). Originallyobserved in a laboratory strain of Streptococcus pneumoniae (13), other workers have From the Sir Patrick Dun Research Laboratory, St. James's Hospital, Dublin 8*, Department of Clinical Microbiology (Trinity College), St. James's Hospital, Dublin 8**, Department of Nephrology , Meath Hospital, Dublin 8*** and formerly from the Department of Clinical Microbiology, St. James's Hospital, Dublin 8, Ireland.