Microplastics, plastic fragments smaller than 5 millimeters, have shown up in oceans, rivers, soils, wildlife and even the human body. Now, new research suggests these particles may pose another risk: they can act as vehicles for harmful microbes.
A study published in Environment International analyzed how different microplastic materials behave once they enter coastal waterways. After two months in the water, the team found that microplastics of all types had become coated with dense bacterial biofilms, including pathogens and bacteria carrying antimicrobial-resistant (AMR) genes.
To test how this happens in real-world conditions, researchers from the University of Exeter and Plymouth Marine Laboratory deployed a set of materials, including common plastics like polystyrene and nurdles, along a waterway that flowed from hospital wastewater toward the open coast. The design allowed scientists to track how microbial communities changed as pollution levels dropped downstream.
“Our research shows that microplastics can act as carriers for harmful pathogens and antimicrobial-resistant (AMR) bacteria, enhancing their survival and spread,” said Pennie Lindeque, a co-author on the study.
Across every site, microplastics consistently accumulated bacteria linked to disease and antibiotic resistance. Polystyrene and nurdles showed the highest levels of AMR-related genetic material, possibly because these plastics can bind antibiotics and promote the dense biofilms that help bacteria exchange resistance genes.
The findings also revealed that some pathogens became more common as particles drifted downstream, suggesting the ocean isn’t diluting the risk as much as once believed. That’s especially important near aquaculture sites, where filter-feeding shellfish can ingest microplastics along with the microbes growing on them.
Researchers stress that the study doesn't show people are being infected by microplastics. Instead, it highlights an emerging pathway by which antimicrobial-resistant microbes can move through the environment, from wastewater to rivers to coastal areas where people swim, fish or harvest seafood.
Volunteers participating in beach cleanups should wear gloves and wash hands afterward, the team said. Improving waste management systems could reduce how many contaminated particles reach the ocean.
As research continues, scientists say the findings underscore how plastic pollution intersects with broader public-health issues, including antibiotic resistance and environmental food safety.
This research was supported by philanthropic contributions from Melissa Murdoch, the Barnsbury Trust and Beach Guardian; by the University of Exeter and Plymouth Marine Laboratory; and by grants from the UK Natural Environment Research Council (NERC) and the Biotechnology and Biological Sciences Research Council (BBSRC).