Seafood as a source of antibiotic resistant Enterococcus spp.

Seafood represents an important source of food for humans worldwide and a concerning source of antibiotic-resistant pathogens. A subset of the Enterococcus spp. isolates was subjected to antibiotic susceptibility tests and genomic analysis. The E. faecalis and E. faecium were the most frequent species isolated. More than two-third of the isolates tested resulted resistant to at least three antibiotics and were classified as multidrug-resistant. Resistance to quinupristin/dalfopristin, tetracyclines, fluoroquinolones and macrolides were particularly frequent. No resistance was observed for daptomycin and nitrofurantoin. We reported intrinsic vancomycin-resistant Enterococcus gallinarium and Enterococcus casseliflavus strains. Interestingly, in two isolates of our collection the optrA gene conferring resistance to oxazolidinone resistance was detected. In Enterococcus thailandicus, the optrA gene showed a chromosomal location, while in E. faecium strain optrA was located in a new transferable plasmid, here named pV662optrA. In conclusion, our study showed that Enterococcus species are ubiquitously present on seafood at retail. The presence of isolates showing resistance to last-resort antimicrobials, such as glycopeptides and oxazolidinones is of great concern for human health and underlines the need to include seafood in the surveillance of antibiotic resistance in food.