South Dakota State University doctoral student Neha Neha, left, and professor Sanjeev Anand examine Listeria colonies, as part of research to improve Listeria risk assessment models. More robust risk assessment models will help food manufacturers enhance food safety protocols and thus protect consumers from foodborne illnesses. (Photo courtesy of South Dakota State University)

About 1,600 Americans become ill from eating foods contaminated with Listeria each year according to the Centers for Disease Control and Prevention. The pathogen’s recent influx in a variety of fresh, frozen and processed foods is reinforcing the importance of understanding how contamination occurs in processing plants.

A recent article by South Dakota State University’s Department of Dairy and Food Science examines the industry’s need for a more comprehensive approach in Listeria risk-assessment.

According to dairy science professor Sanjeev Anand, Listeria contamination has been  traced to niches in food processing environment that provide safe harbor for the bacteria. For example, bacteria on the spout of an ice cream freezer in one commercial ice cream plant was identified as the source of Listeria contamination.

“Listeria is a cold-loving microorganism. Pasteurization and cooking kills Listeria, but the bacteria can grow at temperatures 40 degrees F and above in refrigerators and can even survive freezing,” according to the university’s report.

With the issue of cross contamination in manufacturing environments, researchers are working to determine how Listeria builds up in those settings, what characteristics make it possible, and how it resists cleaning efforts.

To examine the pathogen’s persistence, the scientists will conduct whole genome sequencing of the bacteria, with the goal of understanding the gene expression that leads to colonization.

It will also help them compare resident strains of Listeria, which have the ability to form resilient biofilms in the harborage sites and are difficult to eradicate.

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