Dataset Information

First nosocomial outbreak of vancomycin-resistant Enterococcus faecium expressing a VanD-like phenotype associated with a vanA genotype.

ABSTRACT: Although enterococci expressing acquired vancomycin resistance phenotype have been reported increasingly worldwide, they have been rarely reported in France. From August to December 2004 we faced an outbreak of vancomycin-resistant Enterococcus faecium (VRE) isolates in the nephrology department at Bicêtre Hospital (K.-Bicêtre, France). The expression of the glycopeptide resistance varied among the 26 VRE isolates, with vancomycin MICs ranging from 12 to >256 microg/ml, whereas teicoplanin MICs ranged from 4 to 48 microg/ml. However, several strains appeared to be susceptible to glycopeptides according to disk diffusion testing and expressed resistance only after subculture with glycopeptides. In addition, a heterogeneous expression of glycopeptide resistance was also observed. This so-called VanD-like phenotype of resistance (low-level resistance to vancomycin and mostly susceptibility to teicoplanin) was surprisingly associated with a vanA gene. Plasmid extraction and mating-out experiments indicated that the vanA gene was located on a 200-kb self-transferable plasmid. Pulsed-field gel electrophoresis identified mostly dissemination of a single clone, whereas diffusion of the VanA-positive plasmid in different genomic backgrounds had also occurred. The vanA gene was part of a vanA-type operon for expression of resistance located on a Tn1546-like transposon. Sequencing of this transposon identified insertion of insertion sequence IS16 in the vanY gene that encodes a d,d-carboxypeptidase that might explain in part the peculiar VanD-type phenotype of resistance. This report is the first description of a VRE outbreak in France and underlines the difficulty in detecting this organism due to variability on the expression of the glycopeptide resistance trait, if any.

SUBMITTER: Naas T

PROVIDER: S-EPMC1233916 | biostudies-literature | 2005 Aug

REPOSITORIES: biostudies-literature

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First nosocomial outbreak of vancomycin-resistant Enterococcus faecium expressing a VanD-like phenotype associated with a vanA genotype.

Naas Thierry T Fortineau Nicolas N Snanoudj Renaud R Spicq Colette C Durrbach Antoine A Nordmann Patrice P

Journal of clinical microbiology 20050801 8

Although enterococci expressing acquired vancomycin resistance phenotype have been reported increasingly worldwide, they have been rarely reported in France. From August to December 2004 we faced an outbreak of vancomycin-resistant Enterococcus faecium (VRE) isolates in the nephrology department at Bicêtre Hospital (K.-Bicêtre, France). The expression of the glycopeptide resistance varied among the 26 VRE isolates, with vancomycin MICs ranging from 12 to >256 microg/ml, whereas teicoplanin MICs ...[more]

PMID: 16081891

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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.

Project description:We studied the clinical isolates Enterococcus faecium NEF1, resistant to high levels of vancomycin (MIC, 512 microg/ml) and teicoplanin (MIC, 64 microg/ml); Enterococcus faecium BM4653 and BM4656 and Enterococcus avium BM4655, resistant to moderate levels of vancomycin (MIC, 32 microg/ml) and to low levels of teicoplanin (MIC, 4 microg/ml); and Enterococcus faecalis BM4654, moderately resistant to vancomycin (MIC, 16 microg/ml) but susceptible to teicoplanin (MIC, 0.5 microg/ml). The strains were distinct, were constitutively resistant via the synthesis of peptidoglycan precursors ending in D-alanyl-D-lactate, and harbored a chromosomal vanD gene cluster that was not transferable. New mutations were found in conserved domains of VanS(D): at T(170)I near the phosphorylation site in NEF1, at V(67)A at the membrane surface in BM4653, at G(340)S in the G2 ATP-binding domain in BM4655, in the F domain in BM4656 (a 6-bp insertion), and in the G1 and G2 domains of BM4654 (three mutations). The mutations resulted in constitutivity, presumably through the loss of the phosphatase activity of the sensor. The chromosomal Ddl D-Ala:D-Ala ligase had an IS19 copy in NEF1, a mutation in the serine (S(185)F) or near the arginine (T(289)P) involved in D-Ala1 binding in BM4653 or BM4655, respectively, and a mutation next to the lysine (P(180)S) involved in D-Ala2 binding in BM4654, leading to the production of an impaired enzyme. In BM4653 vanY(D), a new insertion sequence, ISEfa9, belonging to the IS3 family, resulted in the absence of D,D-carboxypeptidase activity. Strain BM4656 had a functional D-Ala:D-Ala ligase, associated with high levels of both VanX(D) and VanY(D) activities, and is the first example of a VanD-type strain with a functional Ddl enzyme. Study of these five clinical isolates, displaying various assortments of mutations, confirms that all VanD-type strains isolated so far have undergone mutations in the vanS(D) or vanR(D) gene, leading to constitutive resistance, but that the Ddl host ligase is not always impaired. Based on sequence differences, the vanD gene clusters could be assigned to two subtypes: vanD-1 and vanD-4.

Dataset Information

First nosocomial outbreak of vancomycin-resistant Enterococcus faecium expressing a VanD-like phenotype associated with a vanA genotype.

Publications

First nosocomial outbreak of vancomycin-resistant Enterococcus faecium expressing a VanD-like phenotype associated with a vanA genotype.

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