The meat and poultry industry has had greater success in fighting the Listeria pathogen in its products than other sectors of the food industry. But that doesn’t mean poultry and meat processors are resting on their laurels when it comes to controlling Listeria. If anything, they’re taking even more steps to stop the pathogen from contaminating plants, equipment and products.

Listeria monocytogenes can be underestimated. Symptoms can include diarrhea, nausea or other gastrointestinal problems. But if the pathogen gets into people’s blood and they contract Listeriosis, 20% of people will die, compared to a much more common pathogen, Salmonella, which kills less than 1% of people who get sick. Listeria causes the highest mortality rate of the major foodborne pathogens.

The other threat from Listeria is that people who are most susceptible are least able to fight it off: people aged 65 or older, pregnant women and newborn children, or individuals who suffer from weakened immune systems.

Six years ago, 147 people suffered Listeria infections from cantaloupes and 33 people died. Last year, there was a multi-state outbreak of Listeriosis tied to frozen vegetables. The people who got sick ranged in age from 56 to 91.

Meat and poultry don’t get off the hook. Deli meats and poultry are most susceptible to Listeria contamination. Other products vulnerable to Listeria are foods that consumers don’t cook, such as produce, spouts and soft cheeses.

“But thanks to the steps we’ve taken in the meat and poultry industry, we seem to have had more success in preventing Listeria,” said Michael Doyle, Ph.D., director of the Univ. of Georgia’s Center for Food Safety, and Regents Professor of Food Microbiology at UGA.

But that’s not to say industry is letting down its guard – it can’t. The Global Food Safety Initiative held its food safety conference at the end of February and beginning of March. Listeria was a major topic of discussion. And in April, the North American Meat Institute held one of its semi-annual Advanced Listeria monocytogenes Intervention and Control Workshops in Kansas City.

John Butts Ph.D., vice-president of research at Land O’Frost Inc. and president of Food Safety by Design LLC, a consulting firm, who spoke at the GFSI meeting, voiced his concerns about the increasing presence of Listeria in food products. An important thrust of the conference was how to deal with the pathogen, and how to detect and prevent it in meat and poultry.

Butts says Listeria monocytogenes (Lm) control is an increasing global-wide challenge.

'Seek and destroy'

While some areas of industry have already addressed the pathogen, using a “seek-and-destroy” approach, along with “best practices” based on employee education, equipment and facility design and environmental monitoring, outbreaks are now being looked into more quickly by using Whole Genome Sequencing (WGS). This is a “fingerprinting” technology increasingly used as an industry and regulatory tool, GFSI participants at the meeting agreed.

“The irony is that there are probably fewer cases of Listeria in the meat and poultry industry. But because of this Whole Genome fingerprinting technology, there are more cases being discovered,” Mr. Doyle said. “And because of this innovative technology, instead of needing a large cluster of cases to tie sicknesses and manufacturing together, Listeria can be traced to a single company or manufacturer even if there are only two or three cases of illness.”

Doug Craven, corporate QC manager of sanitation for Hormel Foods, spoke at NAMI’s Advanced Listeria monocytogenes Intervention and Control Workshop. He said another factor making Listeria different from other pathogens and hard to control, is its ability to survive and grow in the cold.


“It can not only survive, but continue growing in refrigeration up to 32° F. Even in freezing temperatures, it won’t grow, but it will survive; it won’t be killed off. Add that to Listeria’soccurrence in the environment – in soil, on plant walls, contact and non-contact surfaces – it makes it difficult.”

In ready-to-eat (R.-T.-E.) meats, Listeria is an adulterant. In raw meat products that are cooked, the pathogen is killed. In raw products that are not cooked, including non-meat products, Lm can survive – in soil, produce, vegetables, and can be a problem, Mr. Craven said.

The key to control, Mr. Craven said, is the design of plant facilities to manage and prevent bacteria from entering the environment.

“NAMI and the industry have created 10 principles of sanitary design for all processors (non-competitive). They include making equipment cleanable to a microbiological level; materials must be compatible; surfaces must be accessible for cleaning and inspection; equipment must be self-draining to prevent harborage; no hollow areas in equipment; no niches; sanitary operational performance; hygienic design of maintenance enclosures; hygienic compatibility with other plant systems; and validated cleaning and sanitizing protocols.

“It is also very important not to cross-contaminate in plants. As employees enter an R.-T.-E. room, it’s very important for them to make sure they’re not bringing any Lm from the raw side,” Mr. Craven said. There also needs to be periodic 'deep cleaning.'

“Additives have been successful in keeping Listeria out, like sodium lactate and sodium acetate,” Mr. Doyle said, “because they act as antimicrobials, reducing the risk. When I was at the University of Wisconsin, Listeria was one of the first pathogens we worked on. Now these (deli) products are very safe.”

He voiced some concern about the “natural” and “clean label” movement in the industry, because keeping these kinds of additives out will lessen protection against Listeria and other pathogens. Environmental testing and final product testing are very important, he said.

Gaining control

“The two pillars of environmental control of Listeria are management and verification,” Mr. Butts said. “The control has taken place in the U.S. processed meat industry as measured by more than 25 years of U.S.D.A. compliance sampling.”


He said there has not been a direct link of a Listeria illness or death associated with a federally inspected meat plant in the U.S. since 2003. He said FSIS regulatory testing for Listeriamonocytogenes in ready-to-eat meat and poultry products has found decreasing percentages of Lm positives from 1990 to 2015 – dropping from 4.5% in tests in 1990 to 0.5% in 2015.

“The process control for Listeria starts with looking for it,” Mr. Butts said. “Starting with dry cleaning, rinsing, then foaming and rinsing, including looking for growth niches. Then there is sanitizing, and checking effectiveness. Then we’re into production, spelled by breaks to verify control of Listeria during the production cycle.

“There are two types of sampling. There’s aggressive process control sampling, and we can find positives with process control sampling. And if the positives are verified, that indicates process control failure.”

Butts explained how a “seek-and-destroy” investigation is carried out. It begins with a normal cleaning and sanitation process. Assembly of equipment is observed, followed by a post-assembly sanitizer application. Next is normal setup and startup activities, and the operation is stopped before product is placed on the line. Equipment is disassembled and any remaining machine components are disassembled. Then all disassembled line components are cleaned and flooded or heat-sanitized.

“These questions are asked,” Mr. Butts said. “Are all components being adequately sanitized (chemical or heat)? Are GMPs being followed? After disassembling, any suspect areas are inspected and swabbed. Evidence of any unacceptable organic buildup is looked for. Is disassembly and cleaning acceptable? If the aerobic plate count shows the suspect area is a growth niche for Listeria and if it is found, then the suspect area is a harborage site.

“Best practices include having clean, dry floors with no cracks in plants; one tool or no tool equipment disassembly; cleaning ‘out-of-place’ for small parts, equipment subassemblies and hand tools; the importance of cleaning critical air handling systems; cleaning interstitial spaces above processing areas, where mechanical systems often are kept; the physical separation of raw and ready-to-eat products; and the importance of ‘decluttering’ meat and poultry plants."