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Plasmid-mediated vanB glycopeptide resistance in enterococci
N Woodford1, D Morrison, A P Johnson
1Laboratory of Hospital Infection, Central Public Health Laboratory, London, UK.
Abstract:
Enterococcus faecium, which was highly resistant to vancomycin (MIC 256 mg/liter), but susceptible to teicoplanin (MIC 2 mg/liter), caused two distinct episodes of infection on a renal unit in the United Kingdom. Pulsed field gel electrophoresis (PFGE) indicated that a single strain caused the first episode, while the second episode, which occurred 1 year later, involved multiple strains, all of which were distinct from the original strain. Vancomycin resistance in all but one of these strains was mediated by transferable plasmids that carried the vanB glycopeptide 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 been 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 analysis indicated no similarity between the plasmids from the three different centers, all contained a 2.1-kb EcoRV fragment that hybridized with a probe for the vanB gene. This suggests that there has been dissemination of a conserved glycopeptide resistance determinant, of which vanB is a part.
Insights
Highly vancomycin-resistant Enterococcus faecium strains emerged, with resistance transferable via plasmids carrying the vanB gene. This study highlights the dissemination of conserved glycopeptide resistance determinants, including vanB, across different Enterococcus strains and UK centers.
Area of Science:
- Microbiology
- Infectious Diseases
- Genetics
Background:
- Enterococcus faecium infections pose challenges due to antibiotic resistance.
- Vancomycin resistance in enterococci is a significant public health concern.
- The vanB gene confers resistance to glycopeptide antibiotics.
Purpose of the Study:
- To investigate the molecular mechanisms and epidemiology of vancomycin-resistant Enterococcus faecium (VRE) infections.
- To characterize the role of transferable plasmids in the spread of vanB gene.
- To assess the dissemination of conserved glycopeptide resistance determinants in the UK.
Main Methods:
- Pulsed field gel electrophoresis (PFGE) for strain typing.
- Plasmid analysis to identify resistance determinants.
- Hybridization studies using a vanB gene probe.
- Retrospective analysis of a reference collection of enterococcal isolates.
Main Results:
- Two distinct episodes of infection caused by vancomycin-resistant Enterococcus faecium were identified.
- The second episode involved multiple strains, distinct from the initial strain, with resistance mediated by transferable vanB-encoding plasmids.
- Evidence of vanB gene transfer between strains during the second episode was observed.
- Retrospective analysis revealed other vanB-encoding plasmids from different UK centers, sharing a conserved EcoRV fragment.
Conclusions:
- Plasmid-mediated vanB resistance is a significant factor in VRE outbreaks.
- The vanB gene and associated resistance determinants are disseminated across different Enterococcus species and geographic locations.
- Conserved glycopeptide resistance elements contribute to the spread of antibiotic resistance in enterococci.