Microplastics as a novel substrate for antimicrobial resistance: Effects of concentration, composition, and size on E. coli multidrug resistance

Microplastics (MPs) have emerged as a significant environmental pollutant with profound implications for public health, particularly as substrates to facilitate bacterial antimicrobial resistance (AMR). Recently, studies have shown that MPs may accommodate microbial communities, chemical contaminants and genetic material containing AMR genes. This study investigated the effects of MP concentration, composition, and size on the development of multidrug resistance in Escherichia coli. Specifically, we exposed E. coli to varying concentrations of different MP types, including polyethylene (PE), polystyrene (PS), and polypropylene (PP), across a range of sizes (3-10 {micro}m, 10-50 {micro}m, and 500 {micro}m). Results indicated a direct correlation between MP presence and elevated multidrug-resistant (MDR) in E. coli. Notably, MPs exhibited a higher propensity for facilitating resistance than control substrates such as glass, likely due to their hydrophobicity, greater adsorption capacities, and surface chemistries. Furthermore, we observed that co-culture with MPs resulted in biofilm formation. Notably, we found that the bacteria from passaged MPs formed stronger biofilms once the MPs were removed, associated with changes in motility. Thus, we find that MPs also select for cells that are better at forming biofilms, which can lead to recalcitrant infections in the environment and healthcare setting. Our study highlights the immediate need for comprehensive environmental management strategies to mitigate the risk posed by MPs. ImportanceAntimicrobial resistance is one of the worlds most pressing global health crises, with an estimated 10 million deaths per year forecasted by 2050. With the pipeline of antibiotics running dry, it is imperative that mitigation strategies understand the mechanisms that drive the genesis of antimicrobial resistance. One emerging dimension of antimicrobial resistance is the environment. This study highlights the relationship between a widespread environmental pollutant, (MPs), and the rise of drug-resistant bacteria. While it is known that MPs facilitate resistance through several modes (biofilm formation, plastic adsorption rates, etc.), this study fills the knowledge gap on how different types of MPs are contributing to antimicrobial resistance.