Seafood as a source of antibiotic resistant Enterococcus spp

Seafood is a crucial global food source, but its role as a reservoir for antibiotic-resistant pathogens is concerning. This study focuses on the prevalence of antibiotic resistance in retail seafood, using Enterococcus spp. as an indicator. Seven categories of raw seafood were collected from retail markets in Central Italy. Out of 422 samples, 288 tested positive for Enterococcus spp., resulting in a prevalence rate of 68.25% (CI95%: 63.66%-72.51%). The most common species were E. faecalis (48%) and E. faecium (17.4%). Enterococcus spp. was most frequently found in cephalopods, salmon, bivalves, and crustaceans than in sea bass and bream. The odds of Enterococcus spp. recovery were higher in frozen than in fresh samples, while there was no difference between farm-raised and wild-caught seafood. A subset of 102 isolates was selected for antibiotic resistance testing, showing the highest resistance rates to quinupristin/dalfopristin (52.94%) and tetracycline (27.45%). Over 70% of isolates were multidrug-resistant. Additionally, strains resistant to vancomycin and oxazolidinones, two last-resort antimicrobials, were detected. Vancomycin resistance was observed in E. casseliflavus and E. gallinarum, which are naturally resistant due to the vanC chromosomal cluster. The optrA gene, responsible for resistance to oxazolidinones and phenicols, was found in E. thailandicus and E. faecium, where it was located on to a transferable plasmid. In conclusion, this study confirms the widespread presence of Enterococcus spp. in retail seafood. The detection of multi-resistant isolates and resistance to last-resort antimicrobials highlights significant human health risks, stressing the importance of including Enterococcus spp. in seafood antibiotic resistance surveillance.