Researchers at the University of Georgia are studying the risk of Listeria monocytogenes developing a tolerance to sanitizers, with a specific focus on fresh produce production plants.

The project, titled “Possibility, duration and molecular predictors of sanitizer tolerance in Listeria monocytogenes,” is examining the potential for resistance to chlorine and quaternary ammonium compounds. The research will evaluate how different sanitizer levels and lengths of exposure affect the degree of tolerance in selected Listeria strains. Listeria monocytogenes is often responsible for foodborne outbreaks.

Xiangyu Deng, Ph.D., with the University of Georgia, hopes his research project will help the industry make more informed decisions about the need for chemical rotation to fight Listeria. Ultimately, he hopes their results lead to a genetics-based tool to assess the risk of Listeria developing sanitizer tolerance.

The Food and Drug Administration and the U.S. Department of Agriculture’s Food Safety and Inspection Service recommends rotating sanitizers in fresh-cut produce processing facilities to minimize the chances of pathogens developing tolerance. However, there is not much data on whether Listeria monocytogenes specifically develops a tolerance to commonly used sanitizers. Debates continue on whether or how frequently processing facilities should rotate sanitizing agents. To date, Deng has not heard of any confirmed case wher the pathogen developed tolerance to commonly used sanitizers in produce processing facilities. If the pathogen does develop tolerance through sublethal exposure to sanitizers, there is little data that exists to predict how long tolerance will last before reverting to susceptibility, Deng explained.

The research is looking at two ways Listeria may acquire tolerance.  First is acquired resistance which occurs when an organism is exposed to sublethal doses of a control agent. Those that survive commonly display, but don’t genetically acquire, elevated tolerance to the agent. The second is evolved tolerance, which occurs by long-term exposure to sanitizers, establishing evolutionary changes to Listeria genomes.

But if products are rotated and the tolerant organisms are no longer exposed to the original chemical, the population is unlikely to maintain the tolerance indefinitely. Deng hopes this study will help answer how long it takes for susceptibility to return.

This project is funded in part by the Center for Produce Safety (CPS).  The CPS is a collaborative partnership that leverages the combined expertise of industry, government and the scientific and academic communities to focus on providing research needed to continually enhance food safety.