High Occurrence of Multiple-Drug Resistance Mediated by Integron in Aeromonas Isolated from Fish-Livestock Integrated Farms

Fish-livestock integrated farming is a traditional practice in South China and Southeast Asia. The administration of antimicrobial agents in livestock may potentially facilitate the spread of antimicrobial resistance to aquaculture through the drainage of livestock manure. Aeromonas spp. are fish pathogens that are the predominant bacteria in water bodies. The aim of this study was to characterize multiple-drug-resistantAeromonas spp. isolated from integrated and nonintegrated fish-livestock farms and to investigate the occurrence of class 1 integrons. Of the 481 Aeromonas strains examined in this study, isolates from pig manure, fish, and environmental samples from pig-fish or goose-fish integrated farms were significantly more resistant to various antimicrobial agents than those from nonintegrated farms (P < 0.05). High rates of resistance to nalidixic acid and sulfamonomethoxine were observed in the isolates from the integrated farm. Fifty Aeromonas isolates (10.4%) from integrated farms contained class 1 integrons. In addition, 96.0% (48/50) of the integron-positive strains displayed multiple-drug resistance. Ten types of gene cassette arrays were determined by sequencing, including dfrA17, dfrA12-orfF-aadA2, catB8, dfrB4-catB3-aadA1, aac6(6 ')-Ib-cr-arr-3, aac-II-blaOXA-21-catB3, aar2-aacA4-drfA1-orfC, aac(6 ')-Ib-cr, dfrA15, and dfrB4-catB3-blaOXA-10-aadA1. Notably, among the 50 integron-positive isolates, twenty isolates showed integrons located in plasmids, which may facilitate the transmission of resistance in integrated farms. Our investigation confirmed the high prevalence of multiple antimicrobial resistances mediated by class 1 integrons in Aeromonas isolates from integrated farms. Therefore, it is necessary to establish a risk assessment method for antimicrobial resistance in aquaculture.