Composition and antimicrobial resistance profile of Gram- negative microbiota prevalent in aquacultured fish

Aquatic environments are one of the most favorable settings for acquisition and dissemination of antimicrobial resistance. The aims of this study were twofold: (1) to isolate and identify antimicrobial resistant Gram-negative bacteria that are prevalent in fish kept in open aquaculture ponds and (2) to analyse their antimicrobial resistance profiles. One hundred and nineteen isolates from fish resistant to at least one antimicrobial were investigated. The most predominant genera were Pseudomonas, Chryseobacterium, Enterobacteriaceae, and Aeromonas. The highest numbers of multiresistant isolates were found within Pseudomonas spp., and the lowest, in Aeromonas spp. Resistance to beta-lactams was the most common among all of the bacterial genera. The absence or very low rates of resistance to fluoroquinolones, the small number of clinically important resistance genes, and bacterial taxonomic composition suggest that the most widespread resistant bacteria in aquacultured fish are autochthonous microbiota.