How do foodborne pathogens hide from sanitisers?

When ingested, Listeria monocytogenes can be deadly to those with weakened immune systems, as well as pregnant women, the elderly and infants.

While L. monocytogenes can be killed using heat processing, this step isn’t always possible with minimally processed fresh produce that is consumed raw. As a result, much research has been conducted to develop detection technologies and find pre-harvest control strategies to prevent produce contamination.

L. monocytogenes may also survive and persist in food processing environments due to formation of biofilms that co-exists in these environments. Now, Penn State researchers in the US may have gained a better understanding about how L. monocytogenes can survive and persist in fruit-packing plants by evading and surviving sanitisers.

According to their study, which is now available online and will be published in the June issue of the journal Biofilm, biofilms — comprising otherwise harmless microorganisms that attach to each other and the food surface — result in a kind of shield that surrounds and protects the Listeria. The findings may result in changes to sanitation protocols in food-processing facilities, which the researchers believe could help to diminish contamination of food with Listeria.

“We found two groups of microorganisms in the tree fruit packing environments, Pseudomonadaceae and Xanthomonadaceae, that are very good at forming biofilms and protecting Listeria monocytogenes,” said corresponding author Jasna Kovac, the Lester Earl and Veronica Casida Career Development Professor of Food Safety. “Biofilms represent a physical barrier that reduces the effective diffusion and antimicrobial action of sanitisers and is hypothesised to increase L. monocytogenes’ tolerance to sanitisers used in food processing facilities.”

The researchers tested the biofilm-forming ability of assemblages comprising the foodborne pathogens Listeria monocytogenes and environmental microbiota.  Image credit: Penn State

As a result of the biofilms shielding the pathogen, the sanitisers are not as effective in killing Listeria monocytogenes, explained Laura Rolon, who recently earned her doctorate from Penn State and spearheaded the study.

“Our research suggests that if packing facilities are having a recurring problem with Listeria monocytogenes, they may need to assess whether biofilm-forming microorganisms are causing it,” she said.

This study’s results indicate a need to assess the efficacy of commonly used sanitisers against non-pathogenic biofilm-forming microorganisms commonly found in the food processing environments to prevent biofilms from establishing, Kovac explained. The results of further assessments could help inform practical recommendations for the industry, such as application concentrations and times, to prevent biofilm formation and improve the control of Listeria monocytogenes in these environments.

In future workshops and short courses, Penn State Extension educators will communicate the research findings to professional organisations dedicated to sanitation in food-processing facilities, noted study co-author Luke LaBorde, professor of food science and extension specialist.

“The findings of this research project will inform and enhance sanitation protocols and extension training efforts targeted at the tree-fruit industry to effectively control L. monocytogenes,” said LaBorde, an expert in the tracking of Listeria monocytogenes in produce production and processing environments.

Top image credit: iStock.com/siculodoc