Seasonal prevalence and antimicrobial resistance profiles in <i>Enterococcus</i> spp. identified from mussels farmed along the coasts of the Abruzzo region

The present study aimed to investigate the antimicrobial resistance (AMR) circulation through the different seasons in the Enterococcus genus isolated from mussels (Mytilus galloprovincialis) for human consumption and farmed along the coasts of the central Adriatic Sea (Abruzzo region, Italy). A total of 250 mussels were collected, and 32 Enterococci (90.62% Enterococcus faecium and 9.37% Enterococcus durans) were identified using the VITEK 2 system (bioMérieux, France). Antibiograms included 26 molecules used for the treatment of veterinary and human infections. Biomolecular screenings involved 45 genetic determinants responsible for AMR. Results showed mainly resistance against tetracycline (44.44%), vancomycin (27.78%), quinupristin-dalfopristin (16.67%), nitrofurantoin, and linezolid (11.11%). Concerning the antibiotic resistance genes (ARGs), multiplex end-point polymerase chain reaction assays mostly amplified tetC (59.37%), tetD (50.00%), cfr (43.75%), vanA and vanD (37.50%), vatE (21.87%), vatD, poxtA, and qnrS (18.75%), and 52.67% and 35.11% in winter and spring seasons, respectively. The consistent environmental ARG circulation confirms the genetic pollution of marine environments, and the season variable (water temperatures) significantly influences their horizontal circulation and phenotypical expression. The AMR phenomenon, defined as uncontrolled, represents a crucial public health concern that needs to be monitored.