Exposure to a Subinhibitory Sulfonamide Concentration Promotes the Spread of Antibiotic Resistance in Marine Blue Mussels (Mytilus edulis)

Although antibiotic resistance has become a significant and growing threat to public and environmental health, the occurrence and prevalence of this phenomenon in seafood have not been extensively explored. This study aims to evaluate the impact of subinhibitory antibiotic concentrations on the spread of antibiotic resistance in mussels. Marine blue mussels were exposed to 100 mu g/L sulfamethoxazole (SMX); then, the presence of genes conferring resistance to sulfonamides (sul1 and sul2) and the class 1 integron-integrase gene (intI1) and the bacterial community composition associated with the gastrointestinal tract were investigated. Results showed that all analyzed genes were present in mussels, even in those not exposed to SMX. Moreover, exposure to SMX caused a significant increase in the absolute copy number of sul1 in mussels, although no significant changes were observed for sul2 and intI1 genes. Because the bacterial community composition was not affected by SMX exposure, the increase for sul1 may be attributed to its spread within mussel's microbiome due to the pressure exerted by SMX pollution. Overall, our results showed the presence of antibiotic resistance genes (ARGs) in blue mussels and highlighted the contribution of anthropogenic pollution to the spread of ARGs in aquatic organisms.