어류 장내세균에서의 qnr (Quinolone resistance gene) 유전자 검출 및 특성 분석

Abstract

Quinolones are broad-spectrum antimicrobial aganets widely used in both human and veterinary medicine and they are among the most widely used antibiotics in the aquacultures. The extensive use has been associated with worldwide increasing quinolone resistance. Although quinolone resistance commonly results from chromosomal mutation, recent studies indicate that such resistance can also be transferred on plasmids carrying the gene responsible, qnr. Aims of this study was to confirm the prevalence of quinolone resistance genes (qnr) in fish intesinal microflora and identified transfer of qnr. To investigate the prevalence of the qnr genes in various microflora , we are isolated normal microflora of imported ornamental and cultured marine fish on various selective media plate supplemented with ciprofloxacin 0.125㎍/㎖. Each isolated were screened for the qnr genes (qnrA, qnrB, qnrS) by PCR. Among the 78 isolates indicated in intestinal microflora of dwarf gourami, qnrA and qnrS were present in 24.4%, 21.8%, respectively. Among the 93 isolates indicated in intestinal microflora of red seabream, qnrB and qnrS were present in 10.8%, 6.5%, respectively. it is remarkable that dual genes were found in 52.6%, 3.2% in isolates of dwarf gourami and red seabream, respectively. Qnr-positive isolates showed higher MIC levels to quinolones, and ampicillin, tetracycline. Through this results, a variety of intestinal microflora has been already multi-drug resistance. To determine whether the qnr genes were located on plasmids or chromosomes, we were performed transformation to test the mobility of the qnr genes. Qnr was transferred from six of the 24 probe-positive isolates selected randomly and confirmed transformants containing qnrS. Transformants containing qnrS showed 1- to 32-fold increases in quinolone MICs and 128-fold increases in ampicillin MIC of two transformants. In this results, qnrS might be located on plasmid and co-transferred ESBL genes. This study was identified prevalence of qnr genes, MICs of qnr-positive isolates, transfer of qnr gene. We should be made to continuous monitoring and interest of qnr genes and another antibiotic resistance genes in aquaculture.