Listeria Mitigation Plan – Listeria monocytogenes

Plan Objective: define and describe the microorganism Listeria, its environment, means of transmission, methods of causing illness and, most critical, the means of controlling its spread and growth. While Listeria can be found in many ready-to-eat, non-shelf stable foods, the emphasis here is on cooked meats and raw produce.

Listeria defined: Listeria is a facultative, anaerobic, non-spore-forming microorganism. While it grows better in oxygen-deficient environments(anaerobic), it will survive and grow with or without oxygen(facultative), growing in a wide range of environments. Thus, the removal of oxygen by itself will not restrict the growth of Listeria. Since it is not a spore former, it can be controlled through heat treatments such as pasteurization. The fact that makes Listeria a serious risk, and distinguishes it from other microorganisms, is its ability to grow at cold temperatures between 32-39.2 degrees F., refrigeration temperatures.It grows in a wide range of foods, notably most, mild foods with a high water activity (above .92) and pH (above 4.4)

Enzyme growth induced by cold temperatures allows Listeria to withstand colder environments. The presence of flagella (whip-like appendages) allows it to move inside the cell, attaching itself to intestinal bacteria as protection from the human immune system. As with most microorganisms, it grows best in moist, warm environments; however, it can be found in soil, air, and aerosols.

Summary points: Careful temperature controls below 41 degrees F., combined with limited storage under 7 days, will slow the growth of Listeria. The use of preservatives might slow growth by lowering pH and water activity.

Environments: Listeria is found naturally in soil, surface water, produce and decaying organic matter in agricultural settings. It has been isolated in healthy farm animals, deer, boar, cattle, sheep, and pigs and on dairy farms. It can also be found in 10% of healthy humans, raising the potential for healthy carriers, often as late as 30 days after overt symptoms have disappeared.

Summary points: Listeria can easily enter a food service in any manner soil enters, on feet/shoes, soiled uniforms, street clothes, maintenance tools, insects, air from fans, biofilms from incomplete cleaning, contamination between food processing areas, and further possibilities.

Its occurrence is most common in summer months and fluctuates with the length of the growing season, the soil pH, sanitation of irrigation and processing waters used on the crops, the presence of wildlife, birds and livestock and fecal contamination also closely relate to the prevalence of L. monocytogenes during crop production. Even seeds have been found contaminated by Listeria. Crops implicated in foodborne outbreaks have included produce such as mushrooms, celery, melons, apples, lettuce, and corn.

Summary points: Select approved food suppliers who institute HACCP principles in their operations. Further, since Listeria exists in so many different environments, diligence is necessary to control the entry of Listeria into the food establishment.

Primary Foods at Risk: Listeria can be found in foods such as raw sprouts, unpasteurized milk, sandwiches, salads, soft cheeses, cold meats, cold hot dogs, and smoked seafood – ready-to-eat foods. These foods do not include a heat treatment prior to service and are susceptible to further contamination during processing. Our emphasis here is on cooked meats, poultry and produce.

Foodborne Illness: Listeria causes two types of foodborne illness: invasive (referred to as Listeria monocytogenes) and non-invasive types. Most occurrences are non-invasive and relatively mild (symptoms are usually flu-like, fever and diarrhea), occurring on average, 24 hours after eating and lasting 1-3 days.

In contrast, invasive illnesses, most common with highly susceptible populations (young, elderly, pregnant women, immune-compromised) account for 19% of deaths and nearly always require hospitalization. This type of illness may not occur for up to 2 weeks after eating.

Early symptoms include fever, chills, muscle aches, nausea, and diarrhea; however, headache and a stiff neck can result later in the illness. Illness incidence increases with age, usually above 55 years, and usually with urban populations. Since the microorganism can be isolated in a small percentage of humans, possibly from asymptomatic carriers, person to person transmission is possible.

Recommendations: After this discussion, what steps should be taken to limit the spread of Listeria in a food service operation?


1. Inspected and Audit – Every shipment into the facility must be inspected for (a) safe temperatures below 41 degrees F. at the minimum; (b) a clean organized delivery vehicle; and (c) no potential for cross-contamination between ready-to-eat foods and raw meats, poultry, and seafood. Records must be maintained of each delivery

2. Encourage HACCP – Select trained and certified suppliers, with specifications agreed upon prior to each delivery. Encourage suppliers to institute approved HACCP systems at their facilities. When possible, visit suppliers to audit their facilities. Have a system in place to expedite handling when products must be refused or declared recalled.

3. Isolate Deliveries – Establish ‘clean’ designated areas where ready-to-eat foods will be stored and processed. Restrict entry by anyone in street clothes, who use maintenance tools, loading carts, etc. such as delivery or maintenance personnel. Limit their entry into clean areas. Receive shipments away from clean and sanitize processing areas. Employees taking deliveries must wear gloves and smocks/aprons (covering from the knees upward) when moving foods, and immediately change both items after use. Clean and sanitize delivery carts between uses

4. Eliminate Growth – If possible, build or remodel the facility to eliminate ‘hiding’ places for Listeria. Seal pipes and conduits to the walls fill in spaces where cleaning is difficult (between equipment, around pipes)


Employee Education

1. Train employees about the importance of these programs.

2. Use clean uniforms, gloves and head coverings – change from street clothes in a separate room prior to entry into the designated ‘clean’ area(where ready to eat foods will be processed). Cover street shoes to prevent tracking soil.

3. Use designated employees for raw animal foods production or for trash removal; if this is impractical, uniforms and head coverings must be changed, hands washed, when moving out or into the clean area where ready to eat foods are processed.

4. Proper Hand Washing – be certain hand sinks are accessible, and well stocked with hand cleansers and single-use towels, and conduct training to illustrate how to wash hands and when.

5. Employee health records – have an employee health system in place to monitor for symptoms of Listeria and to exclude employees from ready-to-eat production areas.

Sanitation Records

1. Develop Written Sanitation Proceduresthe physical facility (floors, walls, and ceiling), food contact, and non-food contact equipment and utensils all require a specific method for cleaning and sanitizing. Listeria thrives in warm, moist environments such as are found in floor drains, air fans or simply between piping and the walls, annular spaces around the pipes, and behind equipment with limited access. Audit the facility to identify areas needing extra attention and increase the frequency of cleaning. Unless the facility is newly constructed, there will be many areas where more stringent cleaning is needed.

Food regulations require smooth easily cleanable surfaces and equipment; replace any cracked, split, or damaged items where cleaning might be difficult.

Establish a Benchmark establish a monitoring program to sample random surfaces for either generic Listeria or just a general plate count of microorganisms. Due to expense, this might not be frequent but it must be routine. Repeat sampling at a set frequency to determine if the cleaning program has been effective. Establish corrective actions to be instituted if sample results increase. The records will indicate either the success of sanitation efforts or the need for further action.

Establish a Food Benchmark – Have each food analyzed at a set frequency to check for Listeria (generic Listeria and/or a plate count of all microorganisms) but also to know the pH and water activity. The latter will be valuable in determining if the product is shelf stable but also whether further formulations might restrict Listeria growth. It is also a good policy to test incoming shipments.

Biofilms – Biofilms, the thin invisible film created on surfaces by infrequent or inadequate cleaning, allow microorganisms to thrive. Cleaning must be frequent and thorough, at least every 4 hours but depending on how often the areas are in use. Use separate cleaning utensils for ready-to-eat processing areas

1. Establish written procedures with employee training, including what will be cleaned (be specific for each area to be cleaned – floors require a different procedure, for instance), how often, by whom, and the procedure and materials needed to do the job. Train employees about the importance of Food safety programs. Allow them to practice these tasks under observation and establish record-keeping monitoring effectiveness 2. Prevent Cross ContaminationCross contamination can occur through airflow from raw animal food preparation areas, through the failure to separate areas and equipment, through poor employee hygiene, through unsafe food storage, as well as inside the ready-to-eat food processing area itself.

Establish air flow away from ready-to-eat areas, establishing air curtains or other barriers. Clean ventilation filters and fans often, so they do not introduce contamination.

Use care in washing both the floors (use foaming agents rather than high-pressure hoses) and floor drains to avoid the splash and standing water which might be tracked through the facility

Note: Floor drains should be located away from food equipment to avoid backflow, splash, or migration of Listeria into food areas. Where this is not possible, avoid the splash and use diligent cleaning of the floor area.

CONTROL – Temperatures, Date Labels,

Temperatures monitor temperatures of ready-to-eat foods, both in storage as well as in processing. Either holds these foods below 41 degrees F.; or, if they are being prepared, restrict the amount of food to under 2 hours of preparation time.

Use first in first out (FIFO) and clear date marking to be sure foods are used rapidly, prior to any date limits established by the manufacturer or by the ‘7-day use by’ (preparation date plus 6 days) food regulation.

Keep utensils, slicers, and physical facilities for ready-to-eat foods well separated from raw animal foods.

Establish clean separate storage areas for all ready-to-eat food processing items, both in processing as well as inside cold storage. If separate storage is not available, store ready-to-eat foods above and away from raw animal foods. Establish clear large signage and partitions to delineate the different areas.

Monitor this program and keep careful records to indicate any problems and corrective actions.