'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,” Doyle says. “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’s occurrence in the environment – in soil, on plant walls, contact and non-contact surfaces – it makes it difficult.”

In ready-to-eat (RTE) 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, he says.

The key to control, Craven says, 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 RTE room, it’s very important for them to make sure they’re not bringing any Lm from the raw side,” Craven says. There also needs to be periodic “deep cleaning.”

“Additives have been successful in keeping Listeria out, like sodium lactate and sodium acetate,” Doyle says, “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 voices 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 says.

Gaining Control

“The two pillars of environmental control of Listeria are management and verification,” Butts says. “The control has taken place in the US processed meat industry as measured by more than 25 years of USDA compliance sampling.” He notes there has not been a direct link of a Listeria illness or death associated with a federally inspected meat plant in the US since 2003. He says FSIS regulatory testing for Listeria monocytogenes in ready-to-eat meat and poultry products has found decreasing percentages of Lm positives from 1990 to 2015 – dropping from 4.5 percent in tests in 1990 to 0.5 percent in 2015.

“The process control for Listeria starts with looking for it,” Butts says. “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 explains 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,” Butts says. “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,” he says.

“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,” Butts says.