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Detection of an unusual van genotype in a vancomycin-resistant Enterococcus faecium hospital isolate.

ABSTRACT: We highlight the detection of a rare vanM genotype in Enterococcus faecium. This isolate exhibited a VanB phenotype, with high levels of resistance to vancomycin (MIC, >256 mg/liter) and susceptibility to teicoplanin (MIC, 1 mg/liter). It was, however, vanB negative by PCR. Further screening for other van loci revealed the presence of a complete vanM operon.

SUBMITTER: Teo JW

PROVIDER: S-EPMC3232975 | biostudies-literature | 2011 Dec

REPOSITORIES: biostudies-literature

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Detection of an unusual van genotype in a vancomycin-resistant Enterococcus faecium hospital isolate.

Teo Jeanette W P JW Krishnan Prabha P Jureen Roland R Lin Raymond T P RT

Journal of clinical microbiology 20111012 12

We highlight the detection of a rare vanM genotype in Enterococcus faecium. This isolate exhibited a VanB phenotype, with high levels of resistance to vancomycin (MIC, >256 mg/liter) and susceptibility to teicoplanin (MIC, 1 mg/liter). It was, however, vanB negative by PCR. Further screening for other van loci revealed the presence of a complete vanM operon. ...[more]

PMID: 21998432

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Project description:Enterococcus faecium clinical isolates A902 and BM4538, which were resistant to relatively high levels of vancomycin (128 and 64 microg/ml, respectively) and to low levels of teicoplanin (4 microg/ml), and Enterococcus faecalis clinical isolates BM4539 and BM4540, which were resistant to moderate levels of vancomycin (16 microg/ml) and susceptible to teicoplanin (0.25 microg/ml), were studied. They were constitutively resistant by synthesis of peptidoglycan precursors ending with d-alanyl-d-lactate and harbored a chromosomal vanD gene cluster which was not transferable by conjugation to other enterococci. VanX(D) activity, which is not required in the absence of d-Ala-d-Ala, was low in the four strains, although none of the conserved residues was mutated; and the constitutive VanY(D) activity in the membrane fractions was inhibited by penicillin G. The mutations E(13)G in the region of d-alanine:d-alanine ligase (which is implicated in d-Ala1 binding in A902) and S(319)N of the serine involved in ATP binding in BM4538 and a 7-bp insertion at different locations in BM4539 and BM4540 (which led to putative truncated proteins) led to the production of an impaired enzyme and accounted for the lack of d-Ala-d-Ala-containing peptidoglycan precursors. The same 7-bp insertion in vanS(D) of BM4539 and BM4540 and a 1-bp deletion in vanS(D) of A902, which in each case led to a putative truncated and presumably nonfunctional protein, could account for the constitutive resistance. Strain BM4538, with a functional VanS(D), had a G(140)E mutation in VanR(D) that could be responsible for constitutive glycopeptide resistance. This would represent the first example of constitutive van gene expression due to a mutation in the structural gene for a VanR transcriptional activator. Study of these four additional strains that could be distinguished on the basis of their various assortments of mutations confirmed that all VanD-type strains isolated so far have mutations in the ddl housekeeping gene and in the acquired vanS(D) or vanR(D) gene that lead to constitutive resistance to vancomycin.

Dataset Information

Detection of an unusual van genotype in a vancomycin-resistant Enterococcus faecium hospital isolate.

Publications

Detection of an unusual van genotype in a vancomycin-resistant Enterococcus faecium hospital isolate.

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