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Phenotypic and genotypic heterogeneity of glycopeptide resistance determinants in gram-positive bacteria
S Dutka-Malen1, R Leclercq, V Coutant
1Unité des Agents Antibactériens, Unité Associé National de la Recherche Scientifique 271, Institut Pasteur, Paris France.
Abstract:
Gram-positive glycopeptide-resistant bacteria isolated in various hospitals in Europe and in the United States between 1986 and 1988 were collected. Three resistance phenotypes could be distinguished. Thirty-one enterococci were highly resistant to vancomycin and teicoplanin. Resistance was transferable to other enterococci by conjugation for 16 of the 22 isolates that were tested. Homology was detected by hybridization between a probe specific for the vanA gene, which encodes an inducible high-level glycopeptide resistance protein in Enterococcus faecium BM4147, and DNA of the 31 clinical isolates and the 16 corresponding transconjugants. This indicates that a single class of resistance determinants accounts for high-level glycopeptide resistance in enterococci. The strains differed in their biotypes and resistance phenotypes and harbored resistance plasmids of various sizes, suggesting that spread of this resistance phenotype is due to dissemination of a gene rather than of a bacterial clone or of a single plasmid. Four enterococcal isolates were resistant to low levels of vancomycin and susceptible to teicoplanin. Twenty-three coagulase-negative staphylococcal isolates were resistant to teicoplanin and susceptible to vancomycin. These two groups of strains did not hybridize with the vanA probe and did not transfer resistance at a detectable frequency. The vanA gene was not detected in the glycopeptide-producing strains of Amycolatopsis orientalis (vancomycin) and Actinoplanes teichomyceticus (teicoplanin) or in various gram-positive bacteria intrinsically resistant to glycopeptides.
Insights
High-level glycopeptide resistance in enterococci is primarily due to the vanA gene. This resistance determinant spreads through gene dissemination, not solely by bacterial clones or plasmids.
Area of Science:
- Microbiology
- Molecular Biology
- Antimicrobial Resistance
Background:
- Glycopeptide antibiotics like vancomycin and teicoplanin are crucial for treating Gram-positive bacterial infections.
- Emergence of resistant strains poses a significant threat to public health.
Purpose of the Study:
- To investigate the genetic basis of glycopeptide resistance in Gram-positive bacteria isolated in Europe and the US.
- To characterize different resistance phenotypes and their transferability.
Main Methods:
- Collection and phenotypic characterization of resistant bacterial isolates (enterococci and staphylococci).
- Conjugation experiments to assess resistance transfer.
- DNA hybridization using a vanA gene-specific probe.
Main Results:
- Thirty-one enterococcal isolates exhibited high-level resistance to vancomycin and teicoplanin, with resistance transferable in 16 isolates.
- The vanA gene probe hybridized with DNA from these resistant enterococci and their transconjugants, confirming its presence.
- Four enterococci with low-level vancomycin resistance and 23 coagulase-negative staphylococci resistant to teicoplanin did not carry the vanA gene.
Conclusions:
- A single resistance determinant, the vanA gene, accounts for high-level glycopeptide resistance in enterococci.
- Dissemination of the vanA gene, rather than specific clones or plasmids, is the likely mechanism for the spread of this resistance phenotype.