Detection and Characterization of Antimicrobial Resistance and Putative Virulence Genes in Aeromonas veronii Biovar Sobria Isolated from Gilthead Sea Bream (Sparus aurata L.).

The purposes of this study were to investigate the antimicrobial resistance of Aeromonas veronii biovar sobria isolated from gilthead sea bream and to characterize the virulence-implicated genes. Fish samples (n=365) were collected from wholesale and retail markets in Aljouf, Saudi Arabia between 2013 and 2014. A total of 45 A. veronii biovar sobria isolates (12.3%) from those samples were tested for resistance to a range of antimicrobial agents. All strains exhibited 100% resistances to nalidixic acid, carbenicillin, cephalothin, erythromycin, kanamycin, tetracycline, and trimethoprim-sulfamethoxazole. Additionally, the highest susceptibility encountered was to ciprofloxacin (100%). In the present study, we examined the presence of several genes, including aerolysin, elastase, lipase, flagellin, enterotoxin, and DNases, that code for putative virulence factors that may play important roles in bacterial infection. It was found that all of these genes were common in these strains. Several strains isolated from diseased gilthead sea bream were tested for virulence in gilthead sea bream by intraperitoneal injections. The median lethal dose values ranged from 5×10(3) to 5.2×10(9) colony-forming units per fish. These data suggest that commercial gilthead sea bream fish may act as the reservoir for multiresistant A. veronii biovar sobria and facilitate the dissemination of virulence genes.