The study, published today in Applied and Environmental Microbiology, adds a new layer to concerns about the role that the extremely small (less than 5 millimeters in length) pieces of plastic, which are ubiquitous in the environment, play in promoting the emergence and spread of drug-resistant bacteria. While previous studies have shown how microplastics can serve as vehicles on which bacterial communities can form and share resistance genes, this study suggests there's an interaction occurring between the microplastics and bacteria that influences the development of AMR.

Microplastics 'actively drive' development of resistance
To investigate the interaction between bacteria and microplastics, Gross and her colleagues exposed Escherichia coli bacteria grown in liquid media to varying concentrations of different sizes and types of microplastics, including polyethylene, polystyrene, and polypropylene, until biofilm growth was detected. They then added subinhibitory levels of four different antibiotics commonly found in the environment—ampicillin, ciprofloxacin, doxycycline, and streptomycin—and tested for antibiotic susceptibility every 2 days.

For comparison, the researchers tested antibiotic susceptibility in E coli grown without exposure to microplastics. They also measured the minimum inhibitory concentration (MIC, the amount of antibiotic needed to kill bacteria) in cells grown with a single subinhibitory antibiotic with or without microplastics.

Within 10 days, they found that exposure to microplastics led to increased resistance to all four antibiotics compared with E coli grown in liquid media without microplastics. 

Source: https://www.cidrap.umn.edu/antimicrobial-stewardship/microplastics-contribute-evolution-antimicrobial-resistance-study-finds