SPARE-SEA's objectives of measuring antibiotic resistance genes (ARGs) in oyster culture regions included specific experiments to understand the transfer of ARGs among oysters in the wild. For this, a common stock of specific pathogen free-oysters served as the basis for field experiments. The common stock, produced and raised by project partners in Ifremer, Brest, France, were divided and distributed to additional partner institutions: AWI in Sylt (Germany), CNRS in Thau (France) and IRTA in Ebro Delta (Spain). There, they were held in local waters for two weeks among other commercial stocks of oysters produced locally. After the two weeks among other oyster stocks in local waters, each partner collected 60 oysters for analysis of culturable and non-culturable bacteria and their ARGs within. Our data showed that two weeks in a novel environment were sufficient for oysters to acquire several colistin-resistance genes (variants of eptA and mcr) specific to each European environment. This finding has important implications for the potential spread of antimicrobial resistance (AMR) across Europe via transport of oysters, a common and still unregulated practice in aquaculture. This practice has already contributed to the spread of oyster pathogens, such as Vibrio aestuarianus and the OsHV-1 µvar virus, at the European scale.

More details can be found at: https://www.biorxiv.org/content/10.1101/2024.10.10.617683v1