Vancomycin 내성 Enterococcus faecalis의 분자생물학적 특성과 전파 양상
Epidemiology and Molecular Characterization of Vancomycin-Resistant Enterococcus faecalis
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배경: 반코마이신 내성 장알균(vancomycin-resistant enterococci, VRE) 감염은 Enterococcus faecium에 의한 경우가 90% 이상인 반면 Enterococcus faecalis에 의한 경우는 드물다. 이에 본 연구에서는 반코마이신 내성 E. faecalis 분리율이 낮은 원인이 E. faecium의 항균제 내성 획득력 이외의 요인이 존재하는지 여부를 알아보고자 반코마이신 내성 E. faecalis 균주를 대상으로 임상적 특성과 내성유전자 구조분석, 유전적 형별 분석 및 병독성 인자의 분자생물학적 특성을 분석하였다. 방법: 2001년부터 2011년까지 아주대학교 병원 진단검사의학과에서 분리된 반코마이신 내성 E. faecalis 17균주를 대상으로 항균제 감수성 검사, 내성 유전자형, 내성 유전자 구조분석, 병독성 인자 및 pulsed-field gel electrophoresis를 이용한 유전적 연관성을 조사하였다. 결과: 연구기간 동안 분리된 4,235 VRE 균주 중 E. faecium의 균주수는 3,918 (92.5%), E. faecalis 균주수는 95 (2.2%)였다. E. faecalis가 분리된 환자의 경우 E. faecium 감염이 선행된 경우가 67%였다. 내성 유전자형은 모두 vanA형이었다. 내성 유전자 구조 분석에 따른 유형은 3가지로 분류되었고(I형, IIa형 및 IIb형), 모든 균주에서 IS1542와 IS1216V가 삽입되어 있었다. 병독성 인자 esp 유전자 분석 결과 58.8%에서 양성이었고, PFGE를 이용한 균형 분석에서 대상 균주 모두 유전적 연관성은 없었다. 결론: 반코마이신 내성 E. faecalis 감염은 기존의 반코마이신 내성 E. faecium 감염이 있거나 입퇴원의 반복 및 침습적 시술을 자주 받는 환자에서 주로 발생하며 내성유전자는 반코마이신 내성 E. faecium으로부터 수평전이 되었음을 알 수 있었다. [Ann Clin Microbiol 2015;18:76-81]
Abstract
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. (Ann Clin Microbiol 2015;18:-81)
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