Food Safety Magazine


Controlling Listeria monocytogenes in Ready-to-Eat Meat and Poultry Products

By Micreos

Listeriosis, a serious infection caused by the bacterium Listeria monocytogenes, is mainly spread through contaminated food and represents an important public health problem. Outbreaks are reported worldwide on a regular basis. In a recent multistate outbreak in 2011, contaminated cantaloupes killed 32 of 146 people sickened. Pregnant women and newborns as well the elderly and persons with weakened immune systems are especially at risk.

In a Canadian outbreak in 2008, serious illness from listeriosis was confirmed in 57 individuals and eventually cost the lives of 23 people. Deli meat products appeared to be the cause of this outbreak. Contamination probably occurred in slicing machines in specific production lines in the manufacturing plant.

These two recent outbreaks are not isolated events—previous multistate outbreaks resulting in illnesses, deaths, stillbirths and miscarriages were linked to consumption of turkey deli meat. Furthermore, in the first quarter of 2012, at least 10 recalls for suspected L. monocytogenes contamination were reported in Canada and the United States, usually involving ready-to-eat (RTE) meat products, but included sprouts, beef sausage, queso fresco and several other cheeses, salmon, chicken salad sandwiches and cooked eggs.

Listeria monocytogenes and Deli Meats: The Most Prevalent Combination
Researchers at the University of Florida Emerging Pathogens Institute ranked various ‘pathogen + food’ combinations based on the number of illnesses and deaths caused and the associated costs and overall public health burden. Their results indicate that in comparison to other combinations, L. monocytogenes in deli meats is the most prevalent. The U.S. Food and Drug Administration (FDA)/U.S. Department of Agriculture Food Safety and Inspection Service (USDA FSIS) declared this pathogen the number one target for control in RTE meat and poultry products.

Although an FDA/FSIS estimate reports that about 90 percent of human listeriosis cases in the United States are caused by consumption of contaminated RTE deli meats,[1] the understanding of L. monocytogenes transmission in retail and deli operations is limited. Studies indicate that Listeria is regularly found in retail environments and that L. monocytogenes strains are often widely distributed in retail, indicating cross-contamination.[2]

L. monocytogenes is omnipresent and hardy, compared to many other pathogens, surviving common adverse conditions quite well. It even grows at refrigeration temperatures and in low-oxygen environments, such as in vacuum-packaged products, common in the RTE industry. As L. monocytogenes can grow under these conditions in RTE foods, prevention of post-lethality contamination, for instance during packaging, slicing and assembly of food products, is crucial. Hence, prevention of contamination at the manufacturer, the retailer and the consumer’s home are all-important. Good manufacturing practices, stringent sanitation procedures, as well as education of people handling foods, like employees in deli departments and consumers, are key.

In the past two decades, numerous measures were introduced by both industry and regulatory agencies to combat Listeria. The introduction of USDA-FSIS’s 2003 final rule for the control L. monocytogenes in RTE meats was a landmark decision. As industry and consumers continue to raise the bar in their continuous pursuit of higher food safety standards, occasionally new technologies emerge, providing new opportunities for food processors for cost-savings, flavor improvement, a cleaner label and safer products. Phage technology is one of these true innovations.

“Interventions such as LISTEX™ enable food processors to take safety to a different level, explains Mark Offerhaus, CEO of Micreos, a Dutch-based developer of phage products. “A rapid 1–3 log reduction of L. monocytogenes can be achieved on food and food contact surfaces. Nevertheless it should be seen as an integral part of proper hygiene, rather than a replacement of control systems.”

LISTEX™ is an easy to apply, clean label solution to control Listeria. It’s applied through dipping or spraying, withstands a wide range of food processing conditions, does not affect organoleptic properties of the treated products such as texture, odor, color or taste, leaves starter cultures and ‘good bacteria’ unaffected and is non-corrosive.

It is used to address post-lethality contaminations of L. monocytogenes under ‘alternative-2’ or ‘alternative-1’anti-Listeria protocols, as defined by USDA/FSIS. It can be applied in the production of ham, sausages, hot dogs, ground meat and smoked chicken. It is considered a processing-aid under USDA directive 7120 and does not require labelling. It is OMRI listed and is therefore suitable for both natural and organic products.

LISTEX™ kills Listeria rapidly; the effect can be measured within hours. A dose-dependent control of L. monocytogenes is typically observed during shelf life. The surface area and the structure of the food product, the point of contamination and the bacterial load all influence the efficacy of the phage treatment. It can be integrated easily within the daily routine of the normal production process. Phage treatment at the stage where a contamination is most likely to occur is most suitable.

Offerhaus adds, “Our technicians examine each phase of our clients' production process, provide input into local HACCP programs and provide support during trials—on specific application methods and by optimizing the moment and dosage rate of the LISTEX™ phages."

The Power of Phage Technology: Harnessing the Power of Nature
“People are curious about phages,” Offerhaus observed. Bacteriophages—Greek for ‘bacteria-eaters’—were discovered nearly a century ago. They are essential for life on earth, killing a quarter of all bacteria on the planet every day. Phages are omnipresent in our environment, including our skin and gut, and on and in many foodstuffs.

“The control of L. monocytogenes on RTE meat and poultry products is a high priority for the food industry and continues to be a major concern. Typical applications of LISTEX™ on roast beef or hot dogs have a cost-of-use of around a penny per pound. “With LISTEX™, cost effective applications are within reach of every company,” Offerhaus emphasizes and as research confirms, food safety measures actually contribute generously to the bottom line; all stakeholders stand to benefit.”

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2. Sauders B.D., M.D. Sanchez, D.H. Rice, J. Corby, S. Stich, E.D. Fortes, S.E. Roof and M. Wiedmann. 2009. Prevalence and molecular diversity of Listeria monocytogenes in retail establishments. J Food Prot 72(11):2337–2349.