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Abstract
Background
Recently, vancomycin-resistant enterococci (VRE) with the vanA genotype that are susceptible to teicoplanin have been described in Japan, Taiwan, and Korea. The investigators suggested three point mutations in the putative sensor domain of vanS or impairment of accessory proteins VanY and VanZ as an explanation for the VanB phenotype-vanA genotype VRE. In this study, we analyzed Tn1546-like elements to determine the molecular mechanisms responsible for the impaired glycopeptide resistance of clinical VRE isolates with VanB phenotype-vanA genotype from Korea.
Methods
From 2001 to 2004, 28 clinical isolates of Enterococcus faecium with VanB phenotype-vanA genotype were collected from 8 different university hospitals in diverse geographic areas in Korea. For structural analysis of Tn1546-like elements, PCR amplifications for internal regions of Tn1546 were performed. The purified PCR products were directly sequenced with an ABI Prism 3100 DNA sequencer.
Results
The sequence data of the vanS regulatory gene revealed that none of the isolates had any point mutations in this gene. All 28 isolates had a complete or incomplete deletion of vanY gene. Of these, 13 strains represented a complete deletion of vanZ, and 2 strains showed the deletion of nucleotides near the end point of vanX.
References
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Fig. 1.
Dendrogram of E. faecium isolates with VanB phenotype-vanA. To produce the dendrogram, the banding patterns of E. faecium isolates were interpreted by Dice analysis and analysis by the unweighted pair group method with arithmetic averages.
Fig. 2.
The genetic maps of Tn1546 types of E. faecium isolates with VanB phenotype-vanA genotype from Korean hospitals. The positions of genes and open reading frames (orf1 and orf2) and the direction of transcription are marked by dark arrows at the top. The inverted triangles represent IS elements. The positions of the first nucleotide upstream and the first nucleotide downstream from the IS insertion sites are depicted. Solid arrows indicate the transcriptional orientation of the inserted IS elements. Deletions are indicated by dotted lines.
Table 1.
MICs of vancomycin and teicoplanin for clinical VRE isolates with VanB phenotype-vanA
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