High prevalence of VanB2 vancomycin-resistant Enterococcus faecium in Taiwan

Abstract

Thirty-six VanB glycopeptide-resistant Enterococcus faecium isolates were collected from patients in five different hospitals in Taiwan. The vancomycin resistance genes were amplified by the long vanB PCR, which amplifies the 6,373-bp vanB gene cluster including the vanR(B2), vanS(B2), vanY(B2), vanW(B2), vanH(B2), vanB2, and vanX(B2) genes. The deduced amino acid sequences were found to be 95 to 98% homologous to those of the vanB1 gene cluster: VanR(B1), 97%; VanS(B1), 97%; VanY(B1), 96%; VanH(B1), 95%; VanB1, 96%; and VanX(B1), 98%. Restriction enzyme analysis of the long vanB PCR products revealed that all 36 isolates had the same vanB2-specific pattern. DNA sequence analysis of the vanB2 gene, which is a D-Ala-D-Lac ligase gene, revealed that none of the 36 sequences were identical to the previously published vanB2 sequence. Thirty-one isolates had 1 nucleotide different from the published vanB2 sequence. The sequences of the other five isolates differed from the published vanB2 sequence by 2 or 3 nucleotides. Four isolates with a low or moderate resistance to vancomycin (MIC = 4 to 32 microg/ml) were found to have the same leucine-to-methionine change at amino acid position 308 of the vanB2 gene. The genomic DNAs of all 36 isolates were digested with SmaI and then typed by pulsed-field gel electrophoresis (PFGE). Eight different PFGE types (I to VIII) were observed, and type I was found to be prevalent in all hospitals examined in this study. This result suggests that intra- and interhospital dissemination of this E. faecium strain has occurred in Taiwan.

FIG. 1

Analysis of long vanB PCR products. (A) PCR products of VRE harboring the vanB gene cluster amplified with primers VB211 and VB6545R. The sizes of PCR products are indicated on the right-hand side of the gel. Lane M, lambda phage DNA digested with HindIII; lane 1, VanB1 V583; lanes 2 to 5, VanB2 TUH2-18, TSGH1, CG4248, and VRE-1; lane 6, VanB3 VRE45. (B) RFLP analysis of long vanB PCR products by HaeII or BclI digestion. Lane M, 1-kb DNA ladder (Life Technologies, Grand Island, N.Y.); lane 1, VanB1 V583; lanes 2 to 5, VanB2 TUH2-18, TSGH1, CG4248, and VRE-1; lane 6, VanB3 VRE45. The numbers on the left are in base pairs.

FIG. 2

PFGE patterns of SmaI digests of chromosomal DNA from VRE isolates. Lanes M, Lambda DNA-PFGE marker ladder; lanes 1 to 6, TSGH1 (type I), 1716 (type II), VRE-1 (type III), VRE-8 (type IV), SLH476 (type V), and CKU-6 (type VI); lanes 7 to 11, CKU-11 (type VII), CKU-12 (type VIII), VanB1 V583 (type IX), VanB2 TUH2-18 (type X), and VanB3 VRE45 (type XI). The numbers on the right are in base pairs.