Heterogeneously vancomycin-resistant Staphylococcus epidermidis strain causing recurrent peritonitis in a dialysis patient during vancomycin therapy

Methicillin-resistant Staphylococcus epidermidis (MRSE) was recovered over a 2-month period from the dialysis fluid of a peritoneal dialysis (PD) pati ent who experienced recurrent episodes of peritonitis during therapeutic an d prophylactic use of vancomycin, Characterization of five consecutive MRSE isolates by molecular and microbiological methods showed that they were re presentatives of a single strain, had reduced susceptibility to vancomycin, did not react with DNA probes specific for the enterococcal vanA or vanB g ene, and showed characteristics reminiscent of the properties of a recently described vancomycin-resistant laboratory mutant of Staphylococcus aureus, Cultures of these MRSE isolates were heterogeneous: they contained-with a frequency of 10(-4) to 10(-5)-bacteria for which vancomycin MICs were high (25 to 50 mu g/ml) which could easily be selected to "take over" the cultur es by using vancomycin selection in the laboratory. In contrast, the five c onsecutive MRSE isolates recovered from the PD patient during virtually con tinuous vancomycin therapy showed no indication for a similar enrichment of more resistant subpopulations, suggesting the existence of an "occult" inf ection site in the patient (presumably at the catheter exit site) which was not accessible to the antibiotic.