Epidemiology and Molecular Characterization of Vancomycin-Resistant Enterococcus faecalis / 대한임상미생물학회지

BACKGROUND: Vancomycin-resistant Enterococci (VRE) infections are caused by Enterococcus faecium in about 90% of the cases but can also be caused by Enterococcus faecalis. Thus, this study investigates factors that cause a low isolation rate of vancomycin-resistant E. faecalis (VREfs). To this end, the authors study the clinical traits, resistant gene structure, genomic classification, and molecular characteristics of the virulent factor. METHODS: From January 2001 through September 2011, 17 vanA-containing E. faecalis isolates were collected from hospitalized patients at Ajou University Hospital in Korea. Identification, antimicrobial susceptibility testing, and PCR of van and esp genes were performed. Pulsed-field gel electrophoresis (PFGE) was used for strain typing. PCR and sequencing of the internal regions of Tn1546 were performed for structural analysis of the van gene. RESULTS: Of 4,235 VRE infections, 3,918 (92.5%) were caused by E. faecium, and 95 (2.2%) were caused by E. faecalis. In 67% of VREfs infections, there was a preceding occurrence of E. faecium infection. All isolates were of genotype vanA. Our isolates were divided into three types according to the distribution of IS elements integrated into Tn1546 (types I to IIb). The PFGE results showed no clonal relatedness among isolates. CONCLUSION: Our study found that VREfs infections affect patients who have experienced vancomycin-resistant E. faecium. (VREfm) infection or undergo invasive procedures. The VREfs seems to involve the horizontal transfer of Tn1546 transposon from VREfm.

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

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.