Polystyrene Nanoplastics Flip Salmonella Between Offensive and Defensive Modes
Plastic packaging is pervasive in the food supply chain for good reason. It extends shelf life, reduces food waste, and keeps products hygienic during transit. But as plastics degrade - under mechanical stress, UV light, and microbial action - they shed increasingly small particles. Microplastics are now found in virtually every environment on Earth. Their further breakdown produces nanoplastics, particles small enough to interact with individual biological molecules in ways that are only beginning to be understood.
Pratik Banerjee, associate professor in the Department of Food Science and Human Nutrition at the University of Illinois Urbana-Champaign, studies foodborne pathogens and plastic contamination. His team's earlier work examined how nanoplastics interact with E. coli O157:H7, a strain responsible for severe gastroenteritis outbreaks. Their new study, published in the Journal of Hazardous Materials, turns to Salmonella enterica - a bacterium routinely found in meat and poultry and a leading cause of foodborne illness globally.
What Happens When Salmonella Meets Polystyrene
The experimental setup exposed Salmonella enterica to polystyrene nanoplastics, a polymer widely used in food packaging and disposable utensils. Lead author Jayita De, a graduate student in Banerjee's lab, measured changes in gene expression, biofilm formation, and bacterial behavior across different exposure periods and nanoplastic concentrations.
Initial exposure produced a clear defensive mobilization. Virulence-related genes showed increased expression. The bacteria also formed thicker biofilms - organized communities of cells encased in a protective matrix that makes them more resistant to physical removal and chemical treatment. A thick biofilm on food packaging or a cutting board is more difficult to eliminate with standard sanitation procedures than dispersed bacterial cells.
Prolonged exposure produced a different response. Rather than sustaining elevated virulence, the bacteria shifted toward what De describes as defensive mode: conserving resources and energy while maintaining their ability to persist in the environment. If nanoplastic concentrations increased again, Salmonella shifted back toward the more aggressive state. The behavior suggests the bacteria are making adaptive trade-offs in response to nanoplastic-induced stress - marshaling resources for attack when the threat seems manageable and for survival when it proves sustained.
The Antibiotic Resistance Question
A separate finding from the study warrants attention even though it remains preliminary. Banerjee notes that physiological stress from any source can trigger bacterial mechanisms associated with antimicrobial resistance, and that nanoplastics - though not antibiotics themselves - appear to activate resistance-related genes in Salmonella. This process, called cross-resistance, can convert bacteria that were previously susceptible to a particular antibiotic into strains that are not, even without direct antibiotic exposure.
This work is ongoing. Initial findings indicate that polystyrene nanoplastics increase the expression of antimicrobial-resistant genes in Salmonella, but the researchers are careful not to overinterpret results from early-stage laboratory experiments. Whether this translates into clinically meaningful resistance changes, under real food chain conditions and at the concentrations of nanoplastics humans realistically encounter, is an open question that will require substantially more research to answer.
What the Study Does and Does Not Tell Us
Banerjee is explicit about the uncertainty. These experiments were conducted in laboratory conditions at nanoplastic concentrations chosen for experimental tractability, not necessarily because they reflect realistic exposures in commercial food products or kitchen environments. The team does not advocate for abandoning plastic food packaging based on these findings. The food safety benefits of packaging - reduced spoilage, lower waste, maintained hygiene - are real and substantial.
What the research establishes is a phenomenon that deserves systematic investigation: nanoplastics alter the physiology of an important foodborne pathogen in ways that could affect its virulence and persistence. Whether those changes increase actual risk to consumers, under what conditions, and at what concentrations, requires the kind of field-realistic and epidemiologically grounded research that has not yet been done.
Banerjee's group is among the first to examine these interactions from a food safety perspective, and they explicitly invite other researchers to build on this foundation before any policy recommendations can responsibly be made.