Plastic products are ubiquitous in our food supply chain, shedding microplastics into every part of the human ecosystem. As they degrade, microplastics break down into even smaller fragments called nanoplastics — tiny particles that can affect biological molecules in ways not fully understood.
In a new study, researchers at the University of Illinois Urbana-Champaign examined what happens when nanoplastics interact with Salmonella, potentially affecting food safety and human health.
“Salmonella enterica is a major foodborne pathogen that is often found in meat, poultry, and ready-to-eat food. We are testing ground turkey from grocery stores in our lab for a study on food safety, and finding that it is frequently positive for Salmonella.
“If you cook the meat properly, you should not have a problem. However, ground turkey is often packaged in plastic, and we wanted to explore how Salmonella react when they come into contact with plastic polymers,” said senior author Pratik Banerjee.
Banerjee’s team previously studied the interaction of nanoplastics and an E. coli strain responsible for major outbreaks of severe gastroenteritis. In this study, they focused on Salmonella enterica and polystyrene, a commonly used plastic material for food packaging and disposable utensils.
“We examined the physiology of Salmonella in response to nanoplastics, and we found an increased expression of virulence-related genes. The bacteria also formed thicker biofilms, which further indicates they are becoming more virulent,” said Jayita De, a graduate student in Banerjee’s lab and lead author on the paper.
Biofilm is an agglomeration of microorganisms growing together to form a protective layer, increasing survival for pathogenic bacteria under physiological stress. You might see biofilms as a slimy film in your kitchen sink or on your cutting board after handling raw meat.
However, while Salmonella initially showed increased virulence, prolonged exposure to nanoplastics slowed its stress response.
“When the bacteria first encounter nanoplastic particles, they go into offensive mode and become more virulent. But after a while, they start losing their resources and energy, so they switch to defensive mode, which allows them to persist in the environment for a longer time. If the concentration of nanoplastics rises, they can again switch to an offensive mode. It’s a trade-off between offense and defense,” De said.
The overall conclusion is that interaction with nanoplastics induces behavioral changes in Salmonella enterica, but further research is needed to determine the direction and impact of those changes.
Equally concerning is the possibility that nanoplastics can affect antibiotic resistance in Salmonella, Banerjee said.
“Any compound that puts physiological stress on the bacteria can trigger antimicrobial resistance. Nanoplastics are not antimicrobials, but mere exposure to them could convert bacteria that previously were not resistant to a particular antibiotic in a process called cross-resistance,” he explained.
This is the topic of an ongoing study, but initial findings indicate that polystyrene nanoplastics can cause Salmonella to increase the expression of antimicrobial-resistant genes, Banerjee added.
“However, we don’t want to sound the alarm and advocate that people stop using plastics. Plastic packaging provides a lot of benefits, such as reducing food spoilage and waste while keeping expenses low. We don’t know yet whether this is something we should be worried about,” he said.
Banerjee’s research team is among the first to examine the interactions between foodborne pathogens and plastic particles, thereby advancing this emerging field from a food safety perspective. He hopes other researchers around the world will pick up the mantle, because there is a lot more to learn about consequences, risks, and tolerances before any policy recommendations can be made.
