Abstract Microplastics (MPs) have emerged as a significant environmental pollutant with profound implications for public health, particularly as novel substrates for antimicrobial resistance (AMR). Recently, studies have shown that microplastics might play an important role in the development of AMR due to their ability to accommodate not only microbial communities but also chemical contaminants and genetic material containing antibiotic-resistant genes through biofilm formation. This study investigated the effects of MP concentration, composition, and size on the development of multidrug resistance in Escherichia coli to elucidate the potential variables that impact AMR growth. Specifically, we exposed E. coli to subinhibitory levels of antibiotics and varying concentrations of different MP types, including polyethylene (PE), polystyrene (PS), and polypropylene (PP), across a range of sizes (3-10 µm, 10-50 µm, and 500 µm). Results indicated a direct correlation between MP presence and elevated levels of multidrug-resistant (MDR) E. coli strains. Notably, MPs exhibited a higher propensity for inducing resistance than control substrates such as glass, likely due to their hydrophobicity, greater adsorption capacities, and surface chemistries, which facilitate antibiotic binding. Furthermore, we observed that MPs not only fostered higher magnitudes of resistance at faster rates but also contributed to the formation of biofilms, which provide a protective niche for resistant bacteria. Our study underscores MPs urgent and multifaceted role in propagating antimicrobial resistance and highlights the immediate need for comprehensive environmental management strategies to mitigate the risk posed by microplastics. Importance Antimicrobial resistance is one of the world’s 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 to where it begins. One emerging dimension of antimicrobial resistance is the environment. This study highlights the relationship between a widespread environmental pollutant, microplastics, and the rise of drug-resistant bacteria found in the environment. 5 While it is known that microplastics facilitate resistance through several modes (biofilm formation, plastic adsorption rates, etc.), this study fills the knowledge gap on how different types of microplastics are contributing to antimicrobial resistance.

Microplastics as a novel substrate for antimicrobial resistance: Effects of concentration, composition, and size onE. colimultidrug resistance