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What Food Processors Should Know About Listeria Monocytogenes


What Food Processors Should Know About Listeria MonocytogenesListeria monocytogenes, also known as L. monocytogenes or Listeria, is a type of pathogenic bacteria that thrives in moist environments such as soil, water, animals, and decomposing vegetation. It can also survive in harsh environments such as refrigerators, freezers, and food preservation chemicals, making it particularly challenging to address in a food processing environment.

Understanding where Listeria lives and thrives is crucial for food processors when developing strategies to prevent it.  


In what types of food is Listeria found?

According to the FDA, Listeria outbreaks have been linked to:

  • Soft cheeses.
  • Frozen vegetables.
  • Leafy greens.
  • Ice cream.
  • Caramel apples.
  • Sprouts.

Other food products in which Listeria has been identified include raw dairy products, fruits, vegetables, deli meats, hot dogs, and seafood products.


How does Listeria spread?

Listeria can spread during virtually any step in the food supply chain, including:

  • Harvesting.
  • Processing.
  • Preparation.
  • Packing.
  • Transporting.
  • Storing.

Contamination can be caused by a range of sources, including air, water, soil, meat, and produce. During food processing and preparation, the bacteria can be spread from one food to another through contaminated cutting boards, work surfaces, and utensils. During storage and transportation, Listeria will continue to grow, even in a refrigerated environment, so food that has been contaminated can spread the bacteria to other items in cold storage or to the surfaces of refrigeration equipment. When it adheres to storage equipment surfaces, the bacteria can spread to multiple food batches, making it potentially difficult to identify the source of the contamination.   

What are the effects of Listeria transmission?

Eating food that is contaminated with Listeria can lead to a disease called listeriosis, which causes symptoms that range from mild to severe, with the risk of death for certain populations, especially pregnant women, newborns, seniors, and those with compromised immune systems. In addition to fever and mild digestive symptoms, listeriosis can also cause headaches, a stiff neck, confusion, muscle aches, loss of balance, and convulsions. The CDC estimates that 1,600 people get listeriosis and about 260 die from the disease each year.


How can the spread of Listeria be prevented by consumers?

Unlike other common foodborne pathogens, Listeria’s ability to grow under refrigeration means it can be found at many points in the food supply chain. People at every step in the process must be aware of the risks that Listeria presents and the methods for preventing its spread.

For consumers and restaurants, Listeria prevention includes:

  • Setting refrigerators to 40°F and freezers to 0°F.
  • Washing and sanitizing the inside walls and shelves of refrigerators and freezers.
  • Washing and sanitizing cutting boards, countertops, and utensils.
  • Immediately cleaning up spills in refrigerators and freezers.
  • Washing hands after performing sanitizing procedures.

Food processors can also use these tips and more to prevent cross-contamination in facilities.

We’ve created a new guide that outlines proactive steps you can take to overcome common food processing plant sanitation challenges ➤

How can I prevent Listeria in food processing environments?

Addressing cross-contamination is just one method for preventing the spread of Listeria in a food processing environment. Manufacturers should also implement prevention programs to avoid costly outbreaks. This includes regular sanitizing protocols to reduce the presence of bacteria to safe levels on any surface where it might grow, such as:

  • Food handling surfaces.
  • Processing equipment.
  • Walls and ceilings.
  • Floors and drains.
  • Forklifts and other mobile equipment.


Best practices for sanitizing in a food processing environment include:

  • Disassembling equipment.
  • Using products that adhere to vertical walls, ceilings, and smooth surfaces.
  • Following the manufacturer’s recommendations for concentration levels.
  • Leaving sanitizers on surfaces for the minimum recommended contact time.
  • Rinsing or allowing the sanitizer to dry, depending on the product.

Sanitizers reduce bacteria to a safe level, but do not eradicate them completely. Any bacteria that are left behind have the potential to grow, spread, and develop biofilms. This is one reason daily sanitation procedures are critical for preventing the spread of Listeria. When Listeria is detected at levels that are not safe, surfaces should be treated again with a sanitizer or disinfectant to bring them to acceptable levels.  


Learn more about preventing Listeria in your facility

Protecting your food processing plant by preventing the spread of foodborne pathogens such as Listeria also protects your brand. To learn more about best practices for sanitizing and disinfecting in a food processing environment, read The Busy FSQA Manager’s Guide to Proactive Plant Sanitation.

The Busy FSQA Manager's Guide to Proactive Plant Sanitation