A series of studies conducted by the Department of Food Science at the University of Arkansas in Fayetteville, and WBA Analytical Laboratories, has found that Salmonella and other food-borne pathogens are able to attach to reusable plastic containers (RPCs), even after they have been cleaned and sterilized according to industry standards.
The study involved looking at the materials used to make theRPCs at the microscopic level. The containers have become very popular in recent years as the preferred method of shipping produce. The studies were a follow-up to previous research conducted at the University of California-Davis and Canada’s Guelph University that showed visible residues left on the RPCs after the cleaning process. This led to the conclusion that the residues could harbor bacteria.
What the research revealed was something called a biofilm. Pathogenic bacteria are able to defend themselves while continuing to grow by producing a covering film over their colony. The clusters of bacteria communicate with each other, and form a slimy aggregate to defeat antibiotics. This same process of forming a biofilm in the human body can result in an untreatable infection.
The researchers grew Salmonella, Listeria monocytogenes, and E. coli O157:H7 bacteria on the surfaces of RPRs. They then cleaned and sterilized the RPCs according to industry standards. In all cases, the biofilm was not affected by the cleaning, theoretically allowing for the bacteria to contaminate the next batch of produce put into the containers.
“Anytime you start using these things over and over again, you increase the opportunities for pathogens to propagate,” Steven Ricke, co-author of the study and a professor at the University of Arkansas Center for Food Safety. told Food Safety News. “It’s really increasing the chance of bacteria getting fixed to the surface.”
One interesting issue was brought out in this study. The research team examined the RPC surfaces under an electron scanning microscope and discovered the seemingly smooth surface of the plastics were actually more like the lunar surface, full of pock-marked craters and valleys. Ricke said this landscape suggested the rough surfaces are easier for bacteria to colonize.
While scientific studies have suggested that reusable plastic produce shipping containers can harbor pathogens capable of producing biofilms, there has been no evidence to date of any food-borne illnesses being caused by RPCs. But talking about the bacterial cells found on the containers in the study, Ricke said, “These were definitely viable cells, alive and recoverable, so the opportunity is there. Any guess as to where they go is speculation, but if they’re there and they’re alive they’re sitting there like a smoking gun.”