Complete nucleotide sequence of a quinolone resistance gene (qnrS2) carrying plasmid of Aeromonas hydrophila isolated from fish

Aeromonas hydrophila strain AO1 isolated from an infected fish was found to be resistant to several quinolones. A plasmid isolated from the strain AO1, termed pBRST7.6, was cloned and sequenced and shown to be 7621 bp in length with a GC content of 60%. Further analysis confirmed that it contained a gene with 100% identity to qnrS2 genes described in plasmids associated with other Aeromonas species, the product of which usually confers increased resistance to quinolones. The plasmid backbone contained a replication initiation module (repA repC) belonging to the IncQ-family and two genes (mobC and mobB), the products of which are putatively involved in plasmid mobilization. Putative iteron-based origin of replication and characteristic oriT like sequences were also present in the plasmid. The result suggests that Aeromonas spp. carrying plasmids with quinolone resistance genes are potential reservoirs of antimicrobial resistance determinants in the environment.