Diversity of Tn1546 Elements in Vancomycin-Resistant Enterococci Isolated from Korea

Lee, Sun Min; Lee, Wee Gyo; Kim, Young Sun

Abstract

BACKGROUND
The vanA gene cluster of vancomycin-resistant enterococci (VRE) is carried as a part of Tn1546-like elements. In this study we characterized the structure of Tn1546-like elements in Enterococcus. faecium isolated from patients in Korea. The isolates were also typed by pulsed-field gel electrophoresis (PFGE). METHODS: During 2000, 21 clinical isolates of vanA-containing E. faecium were collected from ten university hospitals in Korea. E. faecium BM4147 was used as a control. PFGE was performed on a CHEF-DR III apparatus. For structural analysis of Tn1546, the overlapping PCR amplification of internal regions of Tn1546 was performed. The purified PCR products were directly sequenced by using ABI Prism 3100 DNA SEQUENCER. RESULTS: All isolates were divided into 3 types according to the distribution of insertion sequences (IS elements) integrated Tn1546 elements. Type I and II were characterized by an IS1542 insertion in the orf2-vanR intergenic region and an IS1216V insertion in the vanX-vanY intergenic region. Type III represented two copies of IS1216V at the orf1 and in the vanX-vanY intergenic region as well as IS1542 in the orf2-vanR intergenic region. No isolates were identical to the prototype, which was identical to the predicted pattern for the published sequence of Tn1546. The PFGE results revealed that all strains except A13, C1, A2 and A9 were genetically unrelated. CONCLUSIONS: The distribution of IS in Tn1546-like elements of the Korean isolates is similar to that of the European VREs. Considering the results of PFGF and Tn1546 typing, the horizontal transfer of vanA resistance gene may be occurring among genetically diverse strains of E. faecium in Korea.