Prevalence and antimicrobial resistance of Lactococcus petauri, L. formosensis, and L. garvieae in retail fish, Japan: A pilot study for antimicrobial resistance monitoring of gram-positive bacteria in seafoods.

Antimicrobials are used in aquaculture to treat bacterial infections, and their use could promote the emergence of antimicrobial-resistant bacteria. Monitoring the antimicrobial resistance profiles of fish-derived bacteria, especially those pathogenic to fish and humans, such as Lactococcus petauri, L. formosensis, and L. garvieae, can be essential for assessing the risk of antimicrobial-resistant bacteria. Therefore, we conducted a pilot study to continuously monitor the contamination and antimicrobial resistance of these bacterial species in retail fish in Japan. We purchased domestic seafood fish samples (n = 490), including wild-caught and farm-raised fish, from supermarkets in Japan between 2023 and 2024. We isolated bacteria from 16.1% of the samples, with L. petauri (8.8%) being the most prevalent species, followed by L. formosensis (5.5%) and L. garvieae (2.2%). Oxytetracycline, erythromycin, and lincomycin resistance rates were 11.6%, 5.8%, and 88.4%, respectively, and we detected resistant isolates both in retail wild-caught and farm-raised fish products. The erythromycin- and oxytetracycline-resistant L. petauri isolate harbored the plasmid harboring the multidrug-resistance genes (erm(B), tet(L), and tet(S)). Phylogenetic analysis revealed that genetically similar isolates were present across the same and different supermarkets over several months. These results suggest that L. petauri, L. formosensis, and L. garvieae could be useful indicators for monitoring antimicrobial-resistant bacteria in seafood, and highlight the potential for bacterial cross-contamination throughout the food supply chain.