Waiter, is there some Listeria in my food?

STILLWATER, Okla. – Illness due to Listeria monocytogenes, or listeriosis, can be acquired by consumption of contaminated foods.

Listeria monocytogenes is a foodborne pathogen that first received widespread recognition from a 1983 outbreak linked to pasteurized milk product in Massachusetts and another in 1985 in the Los Angeles area with a Mexican style cheese that resulted in the deaths of 48 of 142 infected individuals, said Peter Muriana, Food & Agricultural Products Center food microbiologist.

“Because of the nature of these products, early research was focused on processing conditions and thermal resistance of Listeria to help identify if processing conditions needed to be changed to address this new foodborne pathogen as well as better detection methods,” Muriana said.

Listeria monocytogenes, one of five species of Listeria and the only one to be considered a human foodborne pathogen, can colonize the intestinal tracts of mammalian, avian and invertebrate species of animals.

As with any intestinal colonizing bacteria, and especially with pathogenic bacteria such as Listeria, Salmonella and E. coli O157:H7, intestinal colonization allows the dispersal of bacteria through fecal droppings.

In this method of dispersal, bacteria are found on foods that do not traditionally support the growth of these organisms, such as vegetables and fruits, and of course, associated with raw meats that are contaminated during slaughter of animals.

“Recognition of the seriousness of illness and fatalities that can result from illness by Listeria monocytogenes prompted both FDA and USDA to set a ‘zero-tolerance’ for L. monocytogenes on ready-to-eat foods, or RTE foods,” Muriana said. “That is, FDA-regulated foods such as cheese and dairy products and USDA-regulated foods such as cold cuts and luncheon meats that do not need further cooking by consumers.”

In order to curtail foodborne illnesses derived from animal-related foodborne pathogens, including Listeria, Salmonella, Campylobacter and E. coli O157:H7, the USDA-FSIS passed the Hazard Analysis and Critical Control Point/Pathogen Reduction Act in 1996 that was implemented from 1998 through 2000 in meat and poultry processing facilities.

During this time, the USDA-FSIS also declared the presence of E. coli O157:H7 in raw ground beef as an ‘adulterant’ making the food unfit for human consumption.

“The meat and poultry processing industries have had much publicity involved with E. coli O157 in raw ground beef and with Listeria monocytogenes in RTE processed meat plants along with various regulations and directives to control these organisms so that they don’t occur in their associated meat products,” Muriana said.

The zero-tolerance Listeria regulation has been difficult for many types of processors of RTE products, including dairy products, luncheon meats, and potato, macaroni, and ham salads, Muriana said.

Processors have argued that the zero-tolerance legislation is unnecessary in foods in which Listeria may be present in low levels at the point of manufacture but may decline due to the inability to survive in these products. For example, Listeria is likely to decline in mayonnaise-containing products due to the acidity of mayonnaise.

“Scientists have indicated the potential for various pathogens, including Listeria, to demonstrate acid-resistance or adaptation to acid when treated with sub-lethal levels of organic acids, thereby proposing caution to allowing the presence of even low levels in RTE foods,” Muriana said. “Proponents of softening some of the zero-tolerance restrictions appeal to these types of situations and point to changes in regulations in other countries that have a regulatory acceptable level of Listeria in foods that do not support its growth.”

During the end of May, 15 trade organizations submitted a citizen’s petition to the FDA. Some of the organizations included the American Bakers Association, American Frozen Food Institute, American Meat Institute, Grocery Manufacturers of America, National Cheese Institute, National Food Processors Association and National Chicken Council.

The organizations proposed that the FDA should amend the regulation regarding Unavoidable Contaminants in Food for Human Consumption and Food-Packaging Material to establish a regulatory limit of 100 colony forming units of Listeria monocytogenes per gram in foods that do not support the growth of Listeria, such as found in France.

Other countries also have similar regulations. For instance, Denmark has six categories of RTE foods with the ultimate target being less than 100 CFU/gram at the point of consumption. For comparison, the USDA and FDA zero-tolerance is 0 CFU/25 gram sample size.

The FDA is accepting public comment on the petition through Aug. 9, 2004.

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CONTACT:

Peter Muriana
Food Microbiologist
Robert M. Kerr Food & Agricultural Products Center
148 FAPC
Stillwater, OK 74078
Phone: 405-744-6071
Fax: 405-744-6313
E-Mail: peter.muriana@okstate.edu

Oklahoma State University, U.S. Department of Agriculture, State and Local Governments Cooperating. The Oklahoma Cooperative Extension Service offers its programs to all eligible persons regardless of race, color, national origin, religion, sex, age, disability, or status as a veteran, and is an equal opportunity employer.

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