The Food Journal and Food, Nutrition & Science

An alliance between The Lempert Report and The Center for Food Integrity

Listeria Update

Listeria Update

Food Safety Update

March 30, 2008

Listeria Update
Last month, the FDA issued new guidance documents to the industry regarding the control of Listeria monocytogenes, more commonly known as Listeria, in refrigerated or ready-to-eat foods (RT-RTE). The documents are designed to help food manufacturers reformulate RT-RTE foods so that they will not support the growth of listeria and so that they will help reduce the potential for listeria contamination in the manufacturing process.
Listeria is a type of bacteria found in soil, ground water and plants. In many cases, animals and people can carry the bacteria in their bodies without getting sick. Persons with weakened immune systems, pregnant women and their unborn babies and newborns, and the elderly, however, are more susceptible to listeriosis, a severe, sometimes life-threatening illness characterized by fever, vomiting and diarrhea. In fact, pregnant women are 20 times more likely to contract listeriosis than other healthy adults. The CDC estimates that 2,500 people become seriously ill with listeriosis each year in the U.S. One in five die from the disease.
Most infections in humans result from consuming contaminated foods, and usually occur in an isolated manner without any pattern. Rarer, outbreak-associated cases are more closely associated with foods that are ready-to-eat (like coleslaw, soft cheeses made with unpasteurized milk, deli meats, etc.) and a result of a processing or production failure. Canned and pasteurized foods are usually considered to be safe from this type of bacteria.
Contamination occurs most frequently when raw or under-processed foods are stored in the same area as cooked foods, when waste bins are not properly maintained or when equipment breaks down. New employees unfamiliar with listeria management practices working with RF-RTE can be an issue too. The FDA recommends that any processor of a RF-RTE food, including processors of fresh-cut fruits and veggies, and processors of frozen fruits and veggies, follow the new standards set out in their guidance documents.
The risk of listeriosis varies greatly among different food categories, according the FDA. Listeria does not grow when the pH of the food is less than or equal to 4.4, or when the food is frozen or close to frozen. Since foods may naturally have a pH or water activity that prevents the growth of listeria, some foods can be deliberately processed to reach these thresholds.
For example, acid can be added to deli-type salads to bring the pH to less than or equal to 4.4. There are also antimicrobial substances that can be introduced to prevent the bacteria from growing in things like soft cheeses. Other useful processes include thermal processing, irradiation, ultraviolet light and high pressure.
The FDA recommends that any product in the potential risk category be treated as if it already contains listeria. Every lot of the ingredient should be tested and testing should occur in regular intervals. Sanitation programs should be specific to RF-RTE foods. Listericidal control measures, when used consistently, should destroy viable cells of listeria and result in a finished food that contains less than .04 cfu/g of the bacteria.
“Retailers can do some of the same things that consumers do to keep foods safe, at the store level. Keep everything clean, make sure that products at risk for listeria do not contaminate other products, and keep the deli case at the proper temperature. Consumers should ask their retailers about the freshness of ready-to-eat and pre-cooked items,” says Danielle Schor, RD, Senior Vice President of Food Safety for the International Food Information Council.
Meanwhile, retailers should educate their consumers on the ways to prevent listeriosis and keep their food safe. Pregnant women and all at-risk consumers should not eat hot dogs or deli meats (unless they are reheated until steaming hot), soft cheeses like feta and Brie, refrigerated pâté, refrigerated smoked seafood like salmon and whitefish (unless used as an ingredient in a cooked dish), and raw or unpasteurized milk.
“Listeria is present in the environment, so if it’s present in the refrigerator, it can actually contaminate a listeria-free processed food a consumer has brought home from the store. Consumers should clean their refrigerators regularly, consume pre-cooked and ready-to-eat foods as soon as possible – deli meats, for example, within three to five days, and make sure their refrigerator temperatures stay at 40 degrees or below,” says Schor.