Microplastics are fueling the rise of deadly superbugs

"Addressing plastic pollution is not just an environmental issue, it is an important public health priority to combat drug-resistant infections," said Neila Gross, the study's lead author and a doctoral student in the laboratory of Professor Muhammad Zaman at Boston University.

As plastic use increases globally, microplastic pollution has become widespread, and wastewater is a major "reservoir." At the same time, antimicrobial resistance is also on the rise, with environmental factors playing a key role. It is well known that microplastics host bacterial communities on their surfaces, a phenomenon known as "plastic balls".

In this study, researchers investigated how microplastics contribute to AMR at a clinically relevant level. They tested different types of plastic - polystyrene (commonly found in packaging peanuts), polyethylene (used in plastic ziplock bags) and polypropylene (commonly found in crates, bottles and jars).

The microplastics, which range in size from 10 microns to half a millimeter (the size of bacteria), were cultured with E. coli for 10 days. Every two days, the scientists measured the minimum inhibitory concentrations (MICs), or the dose of antibiotics required to stop bacterial growth, of four widely used antibiotics. This way, they can track whether the bacteria develop resistance over time.

The researchers found that regardless of size and concentration tested, microplastics promoted multi-drug resistance in E. coli to four of the antibiotics tested (ampicillin, ciprofloxacin, doxycycline and streptomycin) within 5-10 days of exposure.

Researchers have demonstrated that microplastics alone can contribute to the development of AMR. "This means that microplastics significantly increase the risk that antibiotics will be ineffective against a variety of high-impact infections," Gross said. "Previous research has focused on antibiotic-driven resistance without taking into account the role of environmental contaminants such as microplastics. Research on microplastics has focused on resistance factors such as antibiotic resistance genes (ARGs) and biofilms, rather than studying the speed or extent of AMR through their minimum inhibitory concentrations for different antibiotics."

The researchers found that microplastic- and antibiotic-induced resistance tended to be significant, measurable, and stable, even after the antibiotics and microplastics were removed from the bacteria. Ultimately, this means that microplastic exposure may select for genotypic or phenotypic traits that maintain antimicrobial properties independent of antibiotic pressure.

"Our results show that microplastics actively drive the development of resistance in E. coli even in the absence of antibiotics, and that resistance persists after exposure to antibiotics and microplastics," Gross said. "This challenges the idea that microplastics are only passive vectors for drug-resistant bacteria and highlights the role that microplastics play as active hotspots for the evolution of antimicrobial resistance."

Given that polystyrene microplastics promote the highest levels of resistance and that biofilm formation - known to increase bacterial survival and resistance - is a key mechanism, the findings underscore the urgency of addressing microplastic contamination in antimicrobial resistance mitigation efforts.

Compiled from /ScitechDaily