Emerging risk of chronic microplastic exposure: Evolution of Escherichia coli toward antibiotic resistance and pathogenicity

Microplastics (MPs) are widely used and persist in the aquatic environment, leading to inevitable exposure for organisms, concerns have arisen regarding the potential health risks associated with MPs. However, current research has largely overlooked the microbiological effects of chronic exposure to MPs on bacteria, which have significantly health implications. Herein, we exposed susceptible Escherichia coli to an environmentally relevant concentration (1 mg/L) of polystyrene MPs over ~1800 generations (36 days). In parallel, the control group was serially passaged in MPs-free LB medium for 36 days. Our results reveal that the evolved E. coli cells ( E MP ) exhibited significantly increased resistance to oxidative stress (465-fold) and to multiple antibiotics including cefotaxime, ceftriaxone, and kanamycin, as evidenced by inhibition zone decreasing by 0.81–0.96-fold. Additionally, we observed physiological adaptations including flattened morphology, fitness cost, enhanced biofilm formation capacity, and increased cell motility, which decreased the cells' sensitivity to multiple stressors. Notably, these adaptive traits were associated with increased pathogenicity, as demonstrated by higher adhesion to macrophages and intestinal epithelial cells in vitro and more severe bacterial infections in Galler mellonella in vivo . Mechanistically, the observed adaptations were primarily attributed to the regulation of genes involved in the electron transport chain, energy metabolism and two-component systems, which are known to play crucial roles in bacterial stress responses. This study underscores the urgent need to consider and regulate the health risks posed by long-term exposure to persistent and harmful MPs.