The recent identification of glycopeptide intermediate-resistant @entity794 (GISA) clinical isolates has provided an opportunity to assess the stability of the glycopeptide resistance phenotype by nonselective serial passage and to evaluate reversion-associated cell surface changes. Three GISA isolates from the United States (MIC of @entity2176 = 8 microg/ml) and two from Japan (MICs of @entity2176 = 8 and 2 microg/ml) were passaged daily on nutrient agar with or without @entity2176 supplementation. After 15 days of passage on nonselective medium, @entity2176 - and @entity11248 -susceptible revertants were obtained from each GISA isolate as determined by broth dilution MIC. Revertant isolates were compared with parent isolates for changes in @entity2176 heteroresistance, capsule production, @entity2142 phenotype, coagulase activity, and lysostaphin susceptibility. Several revertants lost the subpopulations with intermediate @entity2176 resistance, whereas two revertants maintained them. Furthermore, although all of the parent GISA isolates produced capsule type 5 (CP5), all but one revertant tested no longer produced CP5. In contrast, passage on medium containing @entity2176 yielded isolates that were still intermediately resistant to @entity2176 , had no decrease in the MIC of @entity11248 , and produced detectable CP5. No consistent changes in the revertants in @entity2142 phenotype, lysostaphin susceptibility, or coagulase activities were discerned. These data indicate that the @entity2176 resistance phenotype is unstable in clinical GISA isolates. Reversion of the @entity2176 resistance phenotype might explain the difficulty in isolating @entity2176 -resistant clinical isolates from the blood of @entity1 who fail @entity2176 therapy and, possibly, may account for some of the difficulties in identifying GISA isolates in the clinical laboratory.

Reversion of the glycopeptide resistance phenotype in XXXX clinical isolates.

@entity1 :: ('9606', 'Species') :: ['patients'] @entity2176 :: ('MESH:D014640', 'Chemical') :: ['vancomycin'] @entity794 :: ('1280', 'Species') :: ['Staphylococcus aureus'] @entity11248 :: ('MESH:D017334', 'Chemical') :: ['teicoplanin'] @entity2142 :: ('MESH:D006461', 'Disease') :: ['hemolysis']
@entity794 :: (1280,Species) :: ['Staphylococcus aureus']
