Abstract
Antibiotic resistance genes (ARGs) represent a growing environmental and public health concern, with aquaculture activities recognized as significant contributors to their dissemination in aquatic ecosystems. This study investigated the spatial and seasonal variations of ARGs and mobile genetic elements (MGEs) in benthic biofilms collected from temperate freshwater streams impacted by aquaculture runoff. Samples were collected quarterly over a year from sites directly downstream of fish farms and upstream control locations. Quantitative polymerase chain reaction (qPCR) was employed to quantify selected ARGs (e.g., tetA, sul1, blaCTX-M) and the class 1 integron-integrase gene (intI1). Results indicated significantly higher abundances of all target ARGs and intI1 in biofilms downstream of aquaculture operations compared to control sites, with concentrations decreasing with increasing distance from the effluent discharge points. Seasonal analysis revealed elevated ARG and intI1 levels during warmer months, coinciding with peak aquaculture activity and increased water temperatures. These findings underscore the role of aquaculture in driving ARG enrichment and highlight benthic biofilms as critical reservoirs for resistance determinants, emphasizing the need for comprehensive monitoring and mitigation strategies in freshwater environments.
