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A cluster of VanD vancomycin-resistant Enterococcus faecium: molecular characterization and clinical epidemiology
B E Ostrowsky1, N C Clark, C Thauvin-Eliopoulos
1Department of Medicine, Division of Infectious Diseases, Beth Israel Deaconess Medical Center, Boston, Massachusetts, USA.
Abstract:
VanD-mediated glycopeptide resistance has been reported for an isolate of Enterococcus faecium, BM4339. Three clinical isolates of vancomycin-resistant E. faecium collected from 3 patients during a 6-week period in 1993 had agar dilution MICs of vancomycin and teicoplanin of 128 and 4 microg/mL, respectively. Polymerase chain reaction (PCR) using degenerate primers complementary to genes encoding d-Ala-d-X ligases yielded a 630-bp product that was similar to the published partial sequence of vanD. By use of inverse PCR, vanD, vanHD, and two partial flanking open-reading frames were sequenced. The deduced amino acid sequence of VanD showed 67% identity with VanA and VanB. vanD appeared to be located on the chromosome and was not transferable to other enterococci. The 3 isolates were indistinguishable by pulsed-field gel electrophoresis and differed from BM4339. No other isolates carrying vanD were found in a subset of 875 recent US isolates of vancomycin-resistant enterococci.
Insights
Vancomycin-resistant Enterococcus faecium carrying the vanD gene was identified in three clinical isolates. This vanD gene was chromosomally located and not transferable between bacteria.
Area of Science:
- Microbiology
- Genetics
- Infectious Diseases
Background:
- Vancomycin resistance in Enterococcus faecium is a significant public health concern.
- The vanD gene confers resistance to glycopeptide antibiotics like vancomycin.
Purpose of the Study:
- To characterize vancomycin resistance in clinical isolates of Enterococcus faecium.
- To investigate the genetic basis and transferability of the vanD gene.
Main Methods:
- Agar dilution method to determine Minimum Inhibitory Concentrations (MICs).
- Polymerase Chain Reaction (PCR) and inverse PCR for gene identification and sequencing.
- Pulsed-field gel electrophoresis (PFGE) for strain typing.
Main Results:
- Three clinical isolates of vancomycin-resistant Enterococcus faecium exhibited high-level resistance to vancomycin and teicoplanin.
- The vanD gene was identified and sequenced, showing 67% amino acid identity to VanA and VanB.
- The vanD gene was found to be chromosomally located and not transferable to other enterococci.
- These isolates were distinct from a previously reported vanD-carrying isolate (BM4339) and no other vanD-carrying isolates were detected in a larger sample.
Conclusions:
- The vanD gene in these clinical isolates is chromosomally encoded and not transferable.
- The genetic characterization provides insight into the diversity of vancomycin resistance mechanisms in Enterococcus faecium.
- Surveillance for vanD-mediated resistance is important, though this specific mechanism appears to be non-transmissible in this context.