Micro- and nanoplastics are already a growing public health concern due to dietary exposure via food and water, the extent and health impacts of which are not yet fully understood. The latest study suggests these plastic particles may indirectly affect human health by influencing how pathogens like Escherichia coli behave in water systems.

"It is very important to better understand the adverse effects of the nanoplastics on human health, and not just in humans but also in the environment, which indirectly influences human health," said Jingqiu Liao, Ph.D., Assistant Professor of Civil and Environmental Engineering at Virginia Tech and an author of the study. "The nanoplastics can make the antimicrobial-resistant pathogens better survive, which could be harmful to the environment and would have public health implications."

The study was authored by researchers from Virginia Tech, Rice University, the Chinese Academy of Sciences, the Swiss Federal Institute of Aquatic Science and Technology, and Zhejiang University.

Nanoplastics Strengthened E. coli, Pseudomonas Biofilms

Biofilms are communities of bacteria that attach to surfaces and surround themselves with a protective matrix known as extracellular polymeric substances (EPS). These microbial communities that develop inside drinking water distribution systems can harbor opportunistic pathogens and make them more difficult to eliminate.

To understand how nanoplastics influence biofilm dynamics, the researchers exposed dual-species biofilms comprising E. coli and Pseudomonas aeruginosa to positively and negatively charged polystyrene nanoplastics at environmentally relevant concentrations ranging from 100–1,000 nanograms per liter (ng/L). Positively charged nanoplastics produced the strongest effects.

The researchers found that nanoplastics entered bacterial cells and increased oxidative stress, raising reactive oxygen species (ROS) levels by approximately 2.2-fold. This stress activated dormant bacteriophages, or viruses that infect bacteria, triggering partial lysis of E. coli cells and releasing intracellular material into the surrounding biofilm.

At the same time, transcriptomic and proteomic analyses showed that nanoplastics activated bacterial stress responses, stimulated bacteriophage replication, and enhanced quorum sensing—the chemical communication system bacteria use to coordinate group behavior. As bacteria "talked" to one another, they secreted larger amounts of EPS, producing thicker, denser, and more protective biofilms.

The researchers also observed activation of bacterial antiviral defense systems in response to prophages, which are bacteriophages that insert their own genomes into the DNA of bacterial hosts and destroy the bacterial cells they inhabit while producing large numbers of new virus particles. To defend against these prophages, bacteria deploy Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) of DNA or RNA.

Together, these processes increased extracellular DNA within the biofilm, improved its mechanical strength by approximately 1.5-fold, and significantly increased resistance to chlorine disinfection. Metagenomic analysis of pipeline biofilms suggested these bacterium–phage interactions also promoted more resilient, multi-species biofilm communities.

The authors concluded that stronger, more disinfectant-resistant biofilms could create new challenges for drinking water treatment and distribution systems by making biofilms more difficult to eradicate from infrastructure surfaces.

Future research is necessary to identify the molecular processes that drive the responses of complex biofilms containing multiple microbial species to plastic particles, as well as to understand the role of particle size (i.e., microplastics vs. nanoplastics) on bacterium–phage dynamics.

Findings Build on Emerging Evidence Linking Plastics to Microbial Risks

The new findings add to a growing body of research suggesting that microplastics and nanoplastics can alter bacterial behavior in ways that increase microbial persistence, antimicrobial resistance (AMR), and virulence.

For example, a 2025 study out of Boston University found that microplastics increased AMR and biofilm formation in E. coli, raising concerns that plastic pollution could contribute to the spread of AMR among foodborne pathogens.

Researchers at the University of Illinois Urbana-Champaign have reported similar findings for nanoplastics. One study found that charged nanoplastics altered the growth, viability, physiological stress responses, virulence, and biofilm formation of pathogenic E. coli. Another study showed that nanoplastics increased Salmonella virulence, promoted biofilm formation, and exacerbated AMR, with greater nanoplastic concentrations producing stronger effects.

Taken together, these studies suggest that plastic particles may influence microbial communities through multiple biological pathways, potentially increasing the persistence of pathogenic bacteria in both food matrices and water systems.