다제내성 Acinetobacter와 유출펌프 유전자

Abstract

I. ABSTRACT

Multidrug-resistant Acinetobacter and efflux pump genes

Shim, Jae-Kwang Adviser: Prof. Jang, Sook-Jin,M.D.,Ph.D Dep.of Bio New drug Development Graduate school of Chosun University

Background : Increased expression of chromosomal genes for efflux systems plays a major role in MDR. Among the five superfamilies of efflux pumps, resistance-nodulation-division (RND) systems are the most prevalent in multi-drug resistant Acinetobcter baumannii. Overexpression of AdeABC constitutes a major mechanism of multi-resistance in A. baumannii. The assessment for the role of AdeABC in carbapenem resistance differ from studies to studies. Studies for the role of efflux pump for carbapenem resistance for A. baumannii isolated from Korea are hard to find out. The prevalence of common efflux pumps in CRAB were not known well. The aim of this study is 1) to investigate the role of the AdeABC multidrug efflux pump in the decreased susceptibility of clinical isolates of A. baumannii to meropenem, 2) to assess the frequency of common efflux pump genes in carbapenem-resistant A. baumannii isolates Methods: We determined MIC value by agar dilution test in the absence and presence of carbonyl cyanide m-chlorophenylhydrazone (CCCP), efflux pump inhibitor (EPI), in 119 clinical isolates of A. baumannii and 17 reference strains of Acinetobacter species. We performed RT-PCR to test the expression of the gene of adeB which encode the efflux pumps adeB. The isolates were also tested by PCR for adeB, adeJ and adeE genes.

Results: Real-time PCR identified 6-fold increases in adeB expression in the group of meropenem-resistant isolates compared to that in the group of meropenem-susceptible isolate. The expression of adeB did not correlate with carbapenem resistance, and 20 isolates with absent or negligible expression of this system were still able to achieve high-level resistance. The addition of CCCP led to a fourfold reduction in the MIC of meropenem for 20 isolate, twofold reduction in the MIC of meropenem for 30 isolate and no reduction in the MIC of meropenem for 69 isolate. The overexpression of adeB was found in 76 (88%) of 86 strains of meropenem resistant group and 15 (58%) of 26strains of meropenem susceptible group. The frequencies of the adeB, adeJ and adeE gene were 91%, 92%, and 10%, respectively.

Conclusion: The synergy between meropenem and CCCP was found in 20(17%) of 119 A. baumannii. No definite correlation was observed between the synergy of meropenem with CCCP and adeB overexpression in most strains tested. The adeB overexpression may be induced by other compounds other than meropenem in most isolates in this study. It seems that the increased expression of AdeABC was not an important contributor to meropenem resistance in most strains of crab tested in this study.