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Summary of the Six Article Series on Listeria in Food Plants

By Bob Lijana
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Over the past six months we have shared a series of articles on many practical aspects of managing Listeria. A summary of each of these articles follows immediately below after their respective titles. In addition, we have added a list of additional references on this subject. Links to all the articles in the series are in the Related Articles section below

What is Listeria: Listeria monocytogenes is one of the most virulent food-borne pathogens. It is an extremely strong organism, able to survive a wide pH range and a wide temperature range. These survival characteristics make Listeria a very insidious organism. Just because a food is cooked or has preservatives or has a low pH doesn’t mean that Listeria is not present—it’s quite the tough organism. Assume it’s there.

Listeria-Related Regulations (FDA & USDA): FDA and USDA have an essentially “zero tolerance” policy for Listeria monocytogenes in foods. However, in spite of past mistakes and costly recalls, Listeria-related recalls still occur. All regulations preach an ongoing vigilance to Listeria presence in the plant environment and in the food. Regulators also use DNA testing to find root sources of Listeria, which can prevent untold tragedy. Regulations help protect public health, so they should be used to that end.

Where Listeria Comes From, and How It Moves Around: Listeria is widely distributed in nature, found in soil, water, vegetation, and animal feces. Thus, it is quite easy for it to get into food plants and be transported around that plant. Given this, a wise food safety team always assumes that the organism is present somewhere in the plant. Harborages are all areas in which Listeria can grow; movement vectors are where those harborages intersect with people and equipment moving around. Best practices necessitate that harborages are eliminated and movement vectors are identified and controlled.

How to Find Listeria in the Plant: before you sample for Listeria, make sure senior management across all functions is supportive of this task, and is willing to share the risk of actually finding Listeria. Some companies test for Listeria species, and some test for a marker organism to avoid a zero-tolerance panic. Best practice is to establish, validate, and execute an environmental monitoring program which is based on strategic sampling of sites around the plant. Doing so is hard work, and requires a lot of patience since Listeria is notoriously hard to find.

How to Get Rid of Listeria in the Plant: there are two complementary approaches to managing Listeria: keep it out to begin with, and eradicate it when it is found. Keeping it out is hard, but try anyway—use interventions such as clean uniforms, captive footwear, and sanitizing mats prior to entry into production. And killing it—involve a reputable chemical company who understands food production. Use quaternary ammonium compounds judiciously, strategically, and smartly. Remember, you are rarely ever done!

Communication—The “Choice to Chase”: deciding to “chase” Listeria is a cross-functional decision, residing not only with the Food Safety & Quality Assurance team. Everyone buys in to be educated on actions and consequences, and to share the risk. The overall food safety culture needs to be one of honesty and openness in communication. A culture of support across the board matters significantly to making sure Listeria is managed well. This is also the kind of environment that FSQA professionals can be proud of, knowing they are making a very positive impact on public health and trust.

REFERENCES

  1. Butts, J. 2003. Seek & Destroy: Identifying and Controlling Listeria monocytogenes Growth Niches. Food Safety Magazine. 9 (2). Available at: https://www.food-safety.com/articles/4802-seek-destroy-identifying-and-controlling-listeria-monocytogenes-growth-niches.
  2. CDC. 2016. Etymologia: Listeria. 22(4). Available at: https://wwwnc.cdc.gov/eid/article/22/4/ET-2204_article.
  3. Neogen Corporation and Cornell University. 2025. Environmental Monitoring Handbook for the Food and Beverage Industries, 2nd Edition. Available at: https://www.neogen.com/en/usac/neocenter/resources/food-beverage-environmental-monitoring-handbook/.
  4. 2008. Compliance Policy Guide CPG Sec 555.320 Listeria monocytogenes. Available at: https://www.fda.gov/regulatory-information/search-fda-guidance-documents/cpg-sec-555320-listeria-monocytogenes.
  5. 2017. Draft Guidance for Industry: Control of Listeria monocytogenes in Ready-to-Eat Foods: Guidance for Industry. Available at: https://www.fda.gov/regulatory-information/search-fda-guidance-documents/draft-guidance-industry-control-listeria-monocytogenes-ready-eat-foods.
  6. 2020. Get the Facts About Listeria. Available at: https://www.fda.gov/animal-veterinary/animal-health-literacy/get-facts-about-listeria
  7. 2022. BAM Chapter 10: Detection of Listeria Monocytogenes in Foods. Available at: https://www.fda.gov/media/157717/download.
  8. Foundation for Meat & Poultry Research & Education. 2021. Food Safety Equipment Design Principles. Available at: https://www.meatinstitute.org/sites/default/files/original%20documents/Sanitation%20booklet%202021.pdf.
  9. Jay, J., Loessner, M., and Golden, D. 2005. Modern Food Microbiology. Available at: https://link.springer.com/book/10.1007/b100840.
  10. Jespersen, L., Butts, J., Holler, G., Taylor, J., Harlan, D., Griffiths, M., and Wallace, C. 2019. The Impact of Maturing Food Safety Culture and a Pathway to Economic Gain. Food Control. 98:367-379. Available at: https://www.sciencedirect.com/science/article/abs/pii/S0956713518305863.
  11. Lijana, B. 2021. Whole-Genome Sequencing: A Double-Edged Sword for the Food Industry. Food Quality & Safety. Available at: https://www.foodqualityandsafety.com/article/opinion-whole-genome-sequencing-is-a-double-edged-sword-for-the-food-industry/
  12. Lijana, B. 2024. Checklists: Useful Tools or Traps? Food Safety Tech. Available at: https://foodsafetytech.com/feature_article/checklists-useful-tools-or-traps/
  13. National Fisheries Institute. 2019. Ready-to-Eat Seafood Pathogen Control Guidance Manual. Available at: https://aboutseafood.com/wp-content/uploads/2018/09/3rd-Edition-RTE-Manual-Final-3-15-19.pdf.
  14. Powitz, R., Balsamo, J., Coleman, N., Collins, C., Noonan, G., Radke, V., and Treser, C. 2025. Complexities and Strategies for Controlling Contamination. Environmental Health. 87(6):32. Available at: https://www.researchgate.net/publication/390360674_Complexities_and_Strategies_for_Controlling_Contamination.
  15. SQF Institute. 2020. Food Safety Code: Food Manufacturing. Edition 9. Available at: https://www.sqfi.com/docs/sqfilibraries/code-documents/edition-9/code-pdfs/20227fmin_foodmanufacturing_v3-2-final-w-links.pdf?sfvrsn=7f70c75a_8
  16. FSIS Compliance Guideline: Controlling Listeria monocytogenes in Post-lethality Exposed Ready-to-Eat Meat and Poultry Products. Available at: https://www.fsis.usda.gov/sites/default/files/import/Controlling-Lm-RTE-Guideline.pdf.
  17. Zoellner, C., Ceres, K., Ghezzi-Kopel, K., Wiedmann, M., and Ivanek, R. 2018. Design Elements of Listeria Environmental Monitoring Programs in Food Processing Facilities. Comprehensive Reviews in Food Science and Food Safety. 17: 1156-1171. Available at: https://pubmed.ncbi.nlm.nih.gov/33350161/.
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Communications – The “Choice to Chase” Listeria

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The “choice to chase” Listeria should not and cannot be made lightly. This is not a task to be given solely to the Food Safety & Quality Assurance (FSQA) department. Senior management across the organization needs to understand what this means, be educated on the actions and consequences, share the risk, and share the accolades. In a very real sense, all of this relates to the food safety culture of the company and its business success. Dr. Lone Jespersen addresses these factors in her paper on economic gain and a mature food safety culture.

No company is going to say publicly they would not make a choice to chase. It’s unethical, and bad business practice. However, it’s their actions which are telling. How they chase is what matters. The hierarchy of the chase:

  1. Close your eyes and hope nothing happens.
  2. Put the FSQA organization on the front line to handle any audits and inspections which relate to the microbiological cleanliness of the plant. They are on their own.
  3. Form a FSQA + Sanitation Team that is charged with plant cleanliness. They are on their own.
  4. Provide the FSQA + Sanitation Team whatever it needs to assess Listeria risks in the plant–people, equipment, training, and budget.
  5. Expand the “choice to chase” team to include the HACCP team, and representatives from senior management.
  6. Charge the team with finding Listeria species wherever they may be, and communicating those results to management.
  7. Charge the team with finding Listeria monocytogenes (Lm) wherever it may be, getting DNA results for Lm, and comparing those results with the CDC’s database, PulseNet.

The challenge (and opportunity) with the latter two approaches is that the company will end up with data demonstrating that Listeria exists in the plant. If Listeria is in the plant, it could get in the food. Hence, many senior managers do not want to know these kinds of results, and they enable an organizational culture that does the same. See point #1, above.

Looking for Lm and finding it in non-product zones can be truly enlightening and empowering. Confirming that its DNA is not in the CDC database can be comforting–no one else has found “your” Listeria in their plants or in listeriosis cases. This gives you the freedom to contain your own problem.

In all cases except #1 above, sanitation and microbiological results must be shared properly with senior management. This requires ongoing education, and a competent team that can address contamination (this requires senior management to hire the right people). Why is this important? Of course it’s to make sure everyone is on the same proverbial page regarding the data. But far more importantly, it’s to raise everyone’s awareness of food safety risk to the company’s products.

Sharing data, sharing ideas to solve contamination problems, and sharing effectiveness of corrective actions serve the purpose of sharing the risk across the company, i.e., the senior management team. Said another way, senior management needs to be aware of all the data, at all times.

If leadership listens and provides resources (and stops shipping product when appropriate), then the FSQA team is well supported and can feel empowered to work even harder to make the choice to chase Listeria. This is the kind of culture and support which matters most to making sure Listeria is managed well. It is also the kind of environment FSQA professionals can be proud of, knowing they are making a very positive impact on public health.

This is the 6th in a series of 6 Listeria in Food Plants articles. See the Related Articles below to read the series.

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Where Listeria Comes From, and How it Moves Around

By Bob Lijana
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Listeria is widely distributed in nature, found in soil, water, vegetation, and animal feces. And since it can be found in soil, it has the ability to contaminate vegetables and produce grown in that soil. This can also occur if contaminated manure is used as fertilizer.

Thus, it is quite easy for Listeria to get into a food plant on someone’s shoes, or equipment being brought in from outside, or ingredients coming from a supplier.

Given the ubiquity of Listeria, a good food safety team (and their management) always assumes that the organism is present somewhere in the plant. Even with regular microbiological sampling coming up negative (i.e., no Listeria found), that is not a reason to lower the level of vigilance. Ever.

The insidious nature of Listeria is such that it can hide, even in untoward conditions, and it can be moved around, up, down, and sideways. The same factors which allow Listeria to enter a plant allow it to be transported within that plant.

Let’s talk about “harborages” and “movement vectors.”

Harborages are all areas in a plant which have the necessary conditions for Listeria to grow. Biofilms (resistant coatings which protect the organism) can offer an additional level of security for the organism. Listeria may or may not grow, but it can certainly survive. These areas (e.g., underneath equipment, in drains) are also called “growth niches” in the scientific literature.

Movement vectors are those locations in which harborages intersect with people and equipment moving around the plant. These are the opportunities for Listeria to move. These points (e.g., a fork truck running through contaminated water) are also called “transfer points” in the scientific literature. An example:

  • An employee accidentally drops Listeria-laden potatoes on the floor.
  • The employee walks through those potatoes and across another production line to get a stainless steel scoop to clean up the potatoes.
  • The employee walks back through the clean production line to scoop up the dirty potatoes, throw them in a trash container, and then put the scoop back.
  • Another employee, not observing any of this, picks up that scoop later to sample ready to eat potato salad.

As you can infer, unbeknownst to the employees, the potatoes were harborages for Listeria, and the scoop (and footwear) were movement vectors likely resulting in Listeria getting into food.

Now think about all of the movement and travel of people and equipment that occurs in your own plant. You may even see the following:

  • Fork trucks moving pallets from a warehouse to a product zone.
  • Stainless steel carts wheeled from one line to another.
  • Production operators carrying ingredients from one line to another.
  • Maintenance tool boxes being set on the floor, and then carried to another location.
  • Mixing implements being used and then hung for ready use later without being cleaned.
  • Bowls containing work-in-progress being wheeled across production lines on their way to a cooler.
  • Employees leaving their production line to get to a break area by walking across other production lines that use different allergens than theirs.

Best practices for Listeria control necessitate that harborages are eliminated and movement vectors are identified and controlled. Attacking Listeria in this way can reduce food safety risk dramatically. Note that the root source is almost assuredly a harborage site (a hiding spot for Listeria). So one of the best ways to find that harborage site is by identifying and mapping movement in the plant. Then follow the movement backwards and forwards, and up and down. You may find yourself surprised at where water can run or come from. And therein lie the “eureka” moments.

The objective is to identify the true root source of the Listeria, and eliminate it. This is very different than simply finding some Listeria and tossing sanitizer on it—this is very common, and people are lulled into believing that the Listeria has now been controlled. This is hardly ever the case if the root source has not been eliminated and if the movement vectors have not been identified and actively managed.

See the Related Articles below to read the series.

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Retail Food Safety Forum

Totally Cool, Inc., Recalls All Ice Cream Products Because of Possible Lm Contamination

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According the the FDA’s website, Totally Cool, Inc. of Owings Mills, Maryland is recalling multiple brands of ice cream products, because they have the potential to be contaminated with Listeria monocytogenes. Products were distributed nationwide, and available in retail locations and direct delivery. No illnesses have been reported to date.

The brands involved were Abilyn’s Frozen Bakery, Amafruits, Chipwich, Cumberland Farms, Dolcezza Gelato, Friendly’s, Hershey’s Ice Cream, Jeni’s, LaSalle, Marco, Taharka Brothers, the Frozen Farmer and Yelloh. More than 65 products were recalled, including ice cream cakes and sandwiches, as well as sorbets, according to a list published by the FDA that includes expiration dates.

Totally Cool, Inc. has ceased the production and distribution of the affected products due to FDA sampling which discovered the presence of Listeria monocytogenes. The company continues its investigation and is taking preventive actions. No other products produced by Totally Cool, Inc. are impacted by this recall.