Two widely disseminated strains of Enterococcus faecalis highly resistant to gentamicin and ciprofloxacin from bacteraemias in the UK and Ireland

Abstract

A strong association was observed between high-level resistance to ciprofloxacin and gentamicin for isolates of Enterococcus faecalis collected in the UK and Ireland as part of the BSAC Bacteraemia Resistance Surveillance Programme, 2001. Thus, 60 of 66 E. faecalis isolates with gentamicin MICs ≥ 512 mg/L were highly resistant to ciprofloxacin (MICs ≥ 32 mg/L), compared with only three of 83 E. faecalis isolates with normal gentamicin susceptibility (MICs ≤ 128 mg/L) (P < 0.0001). Pulsed-field gel electrophoresis of Smal-digested genomic DNA was used to investigate 38 representative E. faecalis isolates with the double resistance from 18 hospitals. Based on the criterion of ≥80% banding pattern similarity, two large clusters were observed: cluster 1 included 14 isolates, from seven hospitals, that were related at 84.8% similarity; cluster 2 included 10 isolates, from six hospitals, that were related at 83.3% similarity. Sporadic isolates and small clusters with the double resistance were also observed, but were not closely related to those in clusters 1 and 2. Further work is needed to characterize these two 'epidemic' E. faecalis strains and to investigate the presence of virulence genes.