Fighting Listeria

by Bernard Shire
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A major food-safety concern is back in the news, the recontamination of ready-to-eat (RTE) foods or foods already cooked after processing has taken place. The pathogen once again largely responsible for this recontamination is Listeria monocytogenes (Lm). It can cause a disease called Listeriosis that is particularly dangerous to infants and young children, pregnant women, the elderly and people with weakened immune systems.

RTE products susceptible to Lm, which can survive even in cold refrigerated environments, include lunch meats, hot dogs, spreads and salads, large-diameter sausages, uncured cooked poultry, jerky and roast, corned and cooked beef.

While USDA has recommended the re-cooking of RTE products or treatment with antimicrobials to prevent these products from becoming recontaminated by Lm, there is another important step to keep Listeria monocytogenes out of meat and poultry processing plants altogether – operating a complete cleaning and sanitation program.

Dr. Catherine Cutter, associate professor and food-safety extension specialist in the Department of Food Science at the Pennsylvania State Univ., acknowledges it may be hard for some plants to control pathogens by investing in new, sanitary design of processing equipment. “Unfortunately, small and very-small plants don’t always have money to invest in new equipment; they’re often using equipment that may have been around the plant for quite some time, or equipment they buy from someone else,” which may have been rolled out before the era of sanitary design. “Lm lurks in many plant harborage sites. Luckily, frequent sanitation and cleaning in the plant assume a much higher level of importance and can play a major role in removing pathogens like Lm,” she says.

A great challenge
Cutter says the challenge becomes greater because some of the postcooking product contact surface areas can become contaminated by Lm including saws, dicers and slicers, shelves, containers, casing peelers, hand tools, packaging equipment, conveyors, and tables if used for raw products and not sanitized properly – and cleaning equipment itself.

There are several potential sources of Lm contamination in meat and poultry processing plants, including the employees and their clothing, and the environment, including airborne bacteria from other work areas. But the main source probably is improperly cleaned and sanitized equipment.

She points out some particular reservoirs of Lm, especially in small processing plants, include floors and drains, ceilings and overhead pipes, standing water in a plant, refrigeration units, cleaning tools, overhead rails, forklifts and pallet jacks, maintenance tools and wood pallets.

Once an RTE product is cooked properly, manufacturing a safe product depends on proper sanitation, limited handling of the product and elimination of cross-contamination in the RTE processing areas.

“Slicers are a huge problem. They’re sharp; crews don’t like to break them apart, especially making sure the blades are clean,” Cutter says. “In fact, any space you can get a piece of paper into, that’s a place for bacteria and other pathogens to hide.”

Cleaning and sanitation tips
Effective equipment sanitation steps for crews include the following:
• Dry cleaning, pre-rinsing, foaming and scrubbing and rinsing.

• Application of chemical sanitizers, visual inspection of equipment, drying or removing of standing water (drying is important because it removes the opportunity for Listeria to grow on floors; the pathogen needs moisture to grow).

Baseline microbial testing is important
• Baseline microbial testing of contact and environmental surfaces will help establish the effectiveness of plant sanitation and help cleaning and sanitation crews learn the location of potential sources of contamination.

• These tests can include microbial analyses, like Aerobic Plate Counts (APC), generic Listeria or Listeria species (spp.), or ATP bioluminescence assays.

Recommended frequency of cleaning and sanitation for crews:
• All processing equipment, floors and drains, waste containers and storage areas – daily.

• Walls – weekly. Condensate drip and coolers – weekly to monthly. Freezers – semi-annually.

• Depends on the types of products and the risks involved.

• Equipment and tools used only to process RTE products should be sanitized before and after use.

• Do not place equipment parts on the floor to clean them.

• When cleaning equipment and product storage rooms, crew members must be careful not to splash water from the floor onto the product, possibly contaminating it with bacteria.

• Crews should pay close attention to difficult-to-clean places where pathogens can easily hide.

Effective sanitizers targeting L. monocytogenes:
• Include quaternary ammonia products (quats), chlorine solutions and products containing peracetic acid.

• Sanitation and cleaning crews would be wise to rotate sanitizers every month or two to prevent bacterial resistance against any one sanitizer.

• Choose appropriate acid-based detergents to avoid “soapstone” or hard water buildup leading to biofilms.

• Some crews alternate detergents, which changes the pH and may keep bacteria from adapting to a particular environment.

• Care must be taken not to use chlorine and acid-based detergents at the same time, due to potential hazards to cleanup crews.

Cleaning and sanitation crew members should work with suppliers of these products and/or with sanitation professionals to develop specific usage schemes or plans for each particular operation or task.

This list is to be used only as a guideline. Address specific questions to your supervisor.

Bernard Shire is a free-lance writer based in Lancaster, Pa. He also works as a food safety consultant and writer for Shire & Associates.

M&P’s Sanitation Tips are to be used only as guidelines for cleaning and sanitizing processing facilities. Specific issues and questions should be addressed to a sanitation crew supervisor.
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