Inflow water is a major source of trout farming contamination with Salmonella and multidrug resistant bacteria

摘要

The impact of European aquaculture, namely trout farms, in the spread of antibiotic resistance and/or zoonotic pathogens has been scarcely addressed. Moreover, aquaculture contamination sources and bacterial dissemination routes have been barely explored. In this study, we assessed the contribution of Portuguese land-based intensive rainbow trout farms and retailed market trout to the spread ofSalmonellaand bacteria carrying clinically-relevant antibiotic resistance genes (ARGs) as well as inflow water and feed as possible sources of those contaminants. Cultural and molecular methods were used to analyse 53 fish farm samples (upstream/downstream water and sediments, tanks and trout) and 25 marketed trout. Plasmid-mediated quinolone resistance (PMQR) genes were found in 21% (n = 11/53) of samples (water/sediment/feed/trout), from all collection points (upstream/within/downstream tanks) and seasons, as well as in 12% (n = 3/25) of marketed trout (3 supermarkets). PMQR genes (qnrS1-S2-S3,qnrB7-B19,qnrD1,oqxAB) were detected inEnterobacteriaceaeorAeromonas hydrophila. AnE.colistrain producing extended-spectrum-beta-lactamase SHV-12 was detected in all sampled points of a fish farm.Salmonella(4 serotypes, includingS. Newport-ST118) was detected in 26% (n = 14/53) of the samples from both farms (water/sediment upstream/within tanks). The clinically-relevant plasmid-mediated colistin resistancemcrgenes were not detected. However, colistin resistantS. Abony with new mutations in the chromosomalpmrAandpmrBgenes was observed. IdenticalSalmonellaand SHV-12-producingE.colistrains (by PFGE/MLST) in water upstream and within trout tanks points to inflow-water of trout farms as an important source of pathogenic bacteria and ARG contamination. These results highlight the need to define microbiological standards for water supplying fish farms in the EU and to establish surveillance and control strategies to limit bacterial transmission associated with this fastest growing food sector worldwide.