5 Targets to Test for in Your Production Environment: #1 Listeria

Testing the production environment helps food producers find and eliminate pathogens before they make their way into the final product.

A part of any modern food safety program, environmental monitoring programs, or EMPs, allow producers to find growth niches for dangerous pathogens and are useful in giving early an early indication of any risk of contamination.

But what microorganisms should producers be looking for? In this series, we investigate five targets to test for in your production environment, beginning with Listeria and the pathogenic Listeria monocytogenes.

#1: Listeria

What is Listeria?

Listeria is a genus of bacteria that are gram-positive facultative anaerobes found in soil and water. There are up to 17 Listeria species with one in particular, Listeria monocytogenes, being a human pathogen. Eating food contaminated with L. monocytogenes causes the disease listeriosis, a serious infection in immunocompromised individuals, newborns, elderly and pregnant women. The illness results in a high rate of hospitalizations and a 15-20% mortality rate. High-risk foods such as ready-to-eat meats, dairy, seafood, fruits and vegetables are subject to post-processing environmental contamination with the pathogen. US regulatory agencies (USDA and FDA) maintain a zero-tolerance policy for L. monocytogenes.

Listeria is killed by normal pasteurization temperatures but is more heat tolerant than gram-negative pathogens (such as Salmonella and Shiga toxin-producing E. coli). Listeria can survive freezing temperatures and is able to grow at refrigerated temperatures. Ready-to-eat foods are of major concern for contamination because they can support the growth of the organism during storage and can be consumed without being cooked.

Where does Listeria come from?

Listeria is a very stable organism and can persist in the food processing environment for years. Without proper sanitation and employee hygiene, the pathogen can cross-contaminate both the processing equipment and, eventually, the final product. It thrives in wet, high-salt environments and can form biofilms if not eradicated from the processing environment. Anti-microbial agents (such as pH, moisture level, etc.) and anti-microbial processes (such as fermentation, drying, freezing) can suppress the growth of L. monocytogenes in foodstuffs, but the goal is to prevent the inadvertent cross-contamination of the final product from the processing environment so it does not overwhelm these control measures.

What kinds of process controls work to prevent Listeria?

Traffic patterns, good manufacturing practices (GMPs), sanitary design and sanitation practices are key components to a facility’s hazard analysis and critical control points (HACCP) and preventive control measures for Listeria and L. monocytogenes. Environmental testing is performed to verify the effectiveness of those control programs. If any Listeria species are present then there could be a potential growth niche for the pathogenic L. monocytogenes. Food contact surfaces and non-food contact surfaces are tested for Listeria species according to a robust sampling program. If food contact surfaces test positive for Listeria then finished product testing is required.

What methods do processors use to test?

There are many ways a processor can determine the effectiveness of sanitation and control programs for Listeria (including ATP, total plate count, and Listeria testing).

Rapid methods that test for Listeria species (and Listeria monocytogenes) have proven themselves reliable and are increasing in popularity. Immunoassay-based methods employ antibodies that detect specific proteins, while PCR methods detect DNA. They provide processors with a quick screening tool following the enrichment of environmental samples and food products. A majority of samples will be negative, which allows processors to continue routine operations and release their product faster. Positive test results may indicate potential hot spots or growth niches of Listeria in the plant, indicating that corrective actions must be taken to eliminate the source of the contamination before the finished product is compromised. Processors looking to mitigate the risk of product recalls and human illness associated with L. monocytogenes should carefully map their facilities and track the history of Listeria on their production line.

Stay tuned! The series continues with a look at fecal indicator organisms.