PLASMID-MEDIATED VANB GLYCOPEPTIDE RESISTANCE IN ENTEROCOCCI

Enterococcus faecium, which was highly resistant to vancomycin (MIC 25 6 mg/liter), but susceptible to teicoplanin (MIC 2 mg/liter), caused t wo distinct episodes of infection on a renal unit in the United Kingdo m. Pulsed field gel electrophoresis (PFGE) indicated that a single str ain caused the first episode, while the second episode, which occurred 1 year later, involved multiple strains, all of which were distinct f rom the original strain. Vancomycin resistance in all but one of these strains was mediated by transferable plasmids that carried the vanB g lycopeptide resistance gene. Transfer either of resistance plasmids or the vanB resistance determinant itself to different strains occurred during the second episode. Plasmid-mediated vanB resistance has not be en widely documented. A retrospective study of a reference collection revealed two other vanB-encoding plasmids from an E. faecalis and an E . faecium referred from two further UK centers. Although restriction a nalysis indicated no similarity between the plasmids from the three di fferent centers, all contained a 2.1-kb EcoRV fragment that hybridized with a probe for the vanB gene. This suggests that there has been dis semination of a conserved glycopeptide resistance determinant, of whic h vanB is a part.