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.Practical applicationsThe majority of antimicrobial resistant bacteria that are prevalent in aquacultured fish from open ponds can be treated as natural (autochthonous microbiota). In this study, only a minority of resistant bacteria detected in fish could be associated with polluted waters originating from animal farms or human healthcare facilities. Some strains, particularly the family Enterobacteriaceae that is found in fish, contain clinically important resistance determinants that potentially can be transmitted to human microbiota in cases of inappropriate processing of fish intended for food. With regard to antimicrobial resistant bacteria, measures for control of inflowing waters to aquaculture ponds should be taken in addition to monitoring fish microbiota and its' resistance should be investigated on a regular basis.