Nano- and Microplastics Aided by Extracellular Polymeric Substances Facilitate the Conjugative Transfer of Antibiotic Resistance Genes in Bacteria

The prevalence of antibiotic resistance genes (ARGs) among bacteria has become a global environmental issue. There is a lack of research on whether nano/microplastics could affect ARG transfer between bacteria. In this study, 20, 100 nm, 1 μm, and 1 mm polystyrene (PS) plastic particles were investigated to determine if nano/microplastics could affect the ARG transfer. Nanoplastics and 1 μm microplastics significantly enhanced the transfer efficiency, whereas 1 mm microplastics had no significant effect. Exposure to 0.1 mg/L 20 nm nanoplastics resulted in the highest transfer frequency, which was 8.9-fold greater than that of the control. Exposure to nanoplastics increased the expressions of genes related to outer membrane porin proteins and the key genes of conjugative transfer. Exposure to 1 μm microplastics had no significant effect on the genes related to transfer. After exposure to 1 μm microplastics, the amounts of extracellular polymeric substances (EPS) were increased, which affected the transfer efficiency. The addition of nanoplastics also could stimulate the production of EPS, and the increase of EPS content in the nanoplastic treatment group was also an important factor that affected the transfer frequency. This work provides important insights into the evaluation of the environmental and health risks of ARGs caused by microplastics.