Sub-inhibitory concentrations of antibiotics modulate antimicrobial resistance fate in a biofilm-grazer system

Antimicrobial resistance (AMR) represents an escalating global health challenge, primarily driven by the extensive use of antibiotics in agriculture and medicine. Environmental compartments like soil, water, and biofilms contribute to the spread and persistence of resistance genes. Biofilms and wildlife microbiota are recognized as reservoirs for antibiotic-resistant bacteria and antibiotic resistance genes (ARGs) in aquatic ecosystems. The ecological interactions between biofilms and wildlife gut microbiota, under antibiotic selective pressure, and their implication regarding the dissemination of antimicrobial resistance in aquatic ecosystems is poorly understood. This study examined the impact of sub-inhibitory concentrations of sulfamethoxazole, ciprofloxacin and trimethoprim (10 μg. L^-1) on the resistome in a Biofilm-grazer system, using a river biofilm and Xenopus laevis larvae over a 12-day period. The results indicated that antibiotic pressure resulted in notable variations in microbial composition in both biofilms and gut microbiota. Additionally, comparison of bacterial community composition between gut and biofilm compartments indicated increased microbial exchange between these environments, with stronger effects observed under antibiotic exposure. An increase of the resistome was observed only in biofilm especially under antibiotics exposure. Variations in the grazer's bacterial communities appeared to attenuate the increase of ARGs within the gut. However, grazing activity concomitantly enhanced the resistome abundance and diversity within the biofilm. This study presents an original perspective on the understanding of impact of sub-inhibitory antibiotic concentration on ecosystems though a microcosm experiment, highlighting the necessity for environmental monitoring and further studies across diverse and complex ecological settings to mitigate antibiotic resistance dissemination.