Reusable plastic containers used to transport large amounts of fruits and vegetables to grocery stores can continue to harbor potentially harmful bacteria directly on their surfaces, even after undergoing industry-standard cleaning and sanitizing, according to a new study conducted by researchers from the University of Arkansas and WBA Analytical Laboratories. The study took a microscopically close look at the materials used to make the reusable plastic containers (RPCs) that have gained a foothold in the grocery industry in recent years as a preferred method of transporting produce. The findings suggest that a return to single-use containers for fresh produce might reduce the risk of foodborne illness outbreaks associated with those products, said Steven Ricke, co-author of the study and a professor at the University of Arkansas Center for Food Safety. The researchers allowed Salmonella, Listeria monocytogenes, and E. coli O157:H7 bacteria to grow on the RPC surface and then subjected sample surfaces to cleaning and sanitizing practices typical in the industry. In all cases, the materials still harbored biofilms that protected the bacteria and would theoretically allow bacteria to colonize the next shipment of fruits and vegetables to be put in the containers. “Any time you start using these things over and over again, you increase the opportunities for pathogens to propagate,” Ricke told Food Safety News. “It’s really increasing the chance of bacteria getting fixed to the surface.” He said the study’s objective was to see whether or not bacterial biofilms could survive on the surface of RPC material. After cleaning, they examined RPC samples with a scanning electron microscope (SEM) and found the bacteria on every sample cleaned. “One of the interesting things we saw in the SEM is that it might look fine to the naked eye, but when you look closer it has almost a lunar landscape to it,” Ricke said, suggesting the rough surfaces might be easier for bacteria to colonize. In a future study, the researchers hope to measure the exact percentage of bacteria that remains after the cleaning process, but they don’t have that information based on this study, Ricke said. For now, they were just interested in seeing if the bacteria could survive the cleaning at all. There is no hard evidence linking any foodborne illness outbreaks to lingering contamination on RPCs, and Ricke said he did not want to make any speculations about illnesses caused without evidence. However, he added, the presence of bacteria after cleaning meant that the possibility of disease transmission could not be ruled out. Ricke said that industry needs to look into doing a risk assessment and cost assessment of using RPCs for transporting produce, adding that he knew the suggestion makes him sound “like an academic.” Reusable plastic containers have been under scrutiny from certain food safety academics in recent years. Researchers from both the University of California-Davis and the University of Guelph have conducted studies finding that RPCs are often still contaminated when delivered to produce packers. In November 2014, the president of the Reusable Packaging Association responded to the criticisms, saying that there have been no cases of illness linked to RPCs and that the association had established a food safety standards committee to strengthen the safety of the containers even more.