耐喹诺酮类抗生素的鱼源嗜水气单胞菌中内生质粒pAhW39的克隆及功能

为探究嗜水气单胞菌中内生质粒与菌株对喹诺酮类抗生素耐药表型的关系,实验克隆并分析了分离自湖北仙桃某渔场患病团头鲂的对喹诺酮类抗生素耐药的嗜水气单胞菌W39菌株中的质粒pAhW39.测序结果显示,质粒pAhW39的大小为6739 bp,GC含量为46.13％,低于目前已公布的嗜水气单胞菌染色体DNA的GC含量(60.1％...

Cloning and functional identification of an endogenous plasmid pAhW39 from quinolone-resistant Aeromonas hydrophila isolated from fish

In this study, to investigate the relationship between endogenous plasmids and quinolone-resistant phenotype of Aeromonas hydrophila isolates, a plasmid termed pAhW39, from a quinolone-resistant A. hydrophila strain W39 which was isolated from a diseased Megalobrama amblycephala from a fish farm in Xiantao, Hubei Province, was cloned and characterized. pAhW39 was 6739 bp long, had a GC content of 46.13%, and contained four putative open reading frames (ORFs) (NspV, NspN-like, repB and qnrS2). The GC content of pAhW39 was lower than the GC content of the currently published A. hydrophila chromosomal DNAs ranged from 61.1% to 62.0%, suggesting a possibility that the plasmid pAhW39 might originate from other strains through the horizontal transfer of plasmids. NspV and NspV-like encoded type II endonucleases NspV and NspV-like, respectively. The repB encoded a replication protein RepB and qnrS2 encoded a quinolone resistance protein QnrS2 which usually confers increased resistance to quinolones. pAhW39 was stable in A. hydrophila strain W39 in the absence of selective pressure. Compared with plasmid pAhW39 elimination strain W39-C, the minimum inhibitory concentrations of nalidixic acid and ciprofloxacin against strain W39 were increased 16-fold and 8-fold, respectively, indicating that the plasmid pAhW39 containing qnrS2 might mediate the resistance of strain W39 to quinolones. Comparative genomics analyses revealed that the plasmid pAhW39 had 99.9% DNA sequence identity over its whole length with the plasmid pAER-e58e from Aeromonas sp. strain ASNIH2 isolated from wastewater from a hospital in Maryland, USA. The result implied that plasmid pAhW39 (or pAER-e58e) was widespread and stable, and reminded us that the existence of plasmid-mediated quinolone resistance in Aeromonas spp. in fish might cause a more widespread dissemination of resistance to quinolones in aquaculture, and this should attract more attention.