동일 환자에서 분리된 Enterococcus gallinarum과 E. faecalis 혹은 E. faecium의 Tn1546-like Element 비교

Abstract

Background: Enterococcus gallinarum, an organism often found in the intestine, is intrinsically resistant to low level vancomycin, but some of them are highly resistant to vancomycin due to acquisition of vanA gene. We occasionally detected both vanA carrying E. gallinarum and E. faecalis or E. faecium in the same patients, suggesting transfer of the resistance gene from the latter. In this study, the structures of Tn1546-like elements in E. gallinarum, and E. faecalis or E. faecium from the same patients were compared to determine the clinical significance of the vanA genotype E. gallinarum isolates. Methods: Six pairs of vanA genotype E. gallinarum and E. faecalis or E. faecium were isolated at a tertiary-care hospital in Korea during 2000 to 2004. Species identification was performed by conventional methods. and the vancomycin-resistance genotypes were determined by PCR. For structural analysis of Tn1546-like elements, overlapping PCR amplification and sequencing of the internal regions were performed. Results: All isolates were positive for vanA genes by PCR. The analysis of Tn1546-like elements showed structurally related three types of distribution of IS elements integrated: Type I had insertion of an IS1542 in the orf2-vanR intergenic region, and an IS1216V in the vanX-vanY intergenic region. Type II was similar with Type I but accompanied with the partial and complete deletions of orf1 and orf2. Type III had an IS1216V and an IS1542 in the orf2-vanR intergenic region, and an IS1216V in the vanX-vanY intergenic region. Two of the six vanA clusters in E. gallinarum isolates had structures identical to those in E. faecalis or E. faecium strains isolated from the same patients. However, in some isolate pairs, the origin of Tn1546 cannot be determined, because the structures were not identical, and colonization of multiple clones was supposed. Conclusion: vanA clusters in some E. gallinarum, and in E. faecalis or E. faecium isolates from the same patients had an identical structure, indicating their transfer from the latter. It is assumed that vanA type E. gallinarum can act as a reservoir of vanA gene for interspecies spread.