A new series of studies conducted independently by the University of Arkansas’ Department of Food Science points to a potential avenue for contamination from bacterial residue sometimes found in reusable plastic containers.

While there have been no outbreaks of produce-based foodborne illnesses traced to RPC residues, the Arkansas research, led by the center’s director, Steven C. Ricke, represents a possible entry point for contamination in the food-safety chain.

The research follows up previous studies from University of California-Davis and Canada’s University of Guelph University that shows visible residues remain on some RPCs even after the cleaning process and could potentially harbor bacteria.

The Arkansas study shows that even in materials that appear clean to the naked eye, bacteria like Salmonella, Listeria and E. coli can adhere and create biofilms that resist commercial and industrial cleaning efforts.

“What we’ve done is basically secured visual proof for what has been being talked about in terms of attachment on these types of surfaces,” Ricke said. “These are complex biological organisms and they constantly surprise us. Attachment is a complex process, bacteria attaching to surfaces with the ability to create biofilms. Things can look visibly clean and from a visibility standpoint are clean but you can’t use that as your final decision-making step as to whether something’s clean. When you use a tool such as electron microscope to visualize things you can’t see with the naked eye, it’s more complex than I think we maybe have been believing as we go along.”

Ricke’s research, like the previous studies, could not identify whether the contamination potential is the result of human error or the process for sanitizing reusable packaging -- or a combination of both.

“I wouldn’t rule out both human error and process, but this gets to assumptions being made,” Ricke said. The food industry has “a lot of food-safety regulations in place and we do a very good job, but what we don’t realize is the foodborne pathogens don’t always get the regulatory memo. One of the things we’re thin on, we need more data – we need to understand. I don’t think anybody’s really dug in and looked hard. As a food-safety expert, one of the things that upsets me is assumptions and decisions being made in a vacuum. I don’t know how big a problem this is because the data’s not there one way or another.”

So does the potential exist for foodborne illnesses attributable to residual biofilms?

“Our data would suggest that. How big a problem is it we don’t know,” Ricke said. “I think the way to look at this to some extent is the ability to be exposed to foodborne pathogens is an exercise in probability: The more chances you give foodborne pathogens to come in contact with a particular piece of equipment or surface area, the more you increase potential of risk. You want to avoid opportunities. Things that are reused and equipment in general changes from time to time, it’s not a constant, it’s a bit of a moving target and that’s part of the problem – it’s hard to make it an exact science. We need to go out and do the surveys and see how prevalent the microorganisms are. We need that kind of data in front of us to make some conclusions. Let the data speak for itself – we get into trouble when we don’t do that.”

That means research will inexorably continue, but “that requires patience, time and resources. The problem is people want to rush ahead with judgment without taking a step back and saying, ‘Let’s take a good long look at this.’ This sounds a bit clichéd, but obviously more research needs to be done. We know [bacteria] can attach. How extensive is that attachment? How permeable into food products?” Ricke said.

In addition to “the scanning electron microscope work, we also did a molecular test – which means we had to recover live cells,” he added. “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.”