Health Care

By Arlene Schag

Listeria are mainly soil bacteria, though as a pathogen they are food-borne. The illness caused by the bacteria in people is called listeriosis. Listeria monocytogenes is estimated to cause at least 43 percent of food-borne illness in the United States.

The ability of Listeria to inhabit a wide range of environments coincides with the presence of 331 genes encoding different transport proteins, comprising 11.6% of the total gene compliment of L. monocytogenes. Listeria also has an extensive regulatory repertoire occupying 7.3% of the total genome.

The bacteria propel themselves through the cytoplasm of an infected cell using a tail composed of actin. Both pathogenic and innocuous forms of listeria have the ability to form biofilms, which allow them to attach to solid surfaces where they proliferate and become extremely difficult to remove.

While most bacteria grow poorly when temperatures fall below 40°F, Listeria survives at temperatures from below freezing to body temperature, and grows best at the 0°F to 50°F range. Listeria challenges us because of its ability to grow in diverse environments.

Food processing plant surveys have found Listeria in the following locations (listed approximately in the order of prevalence):

• floors

• drains

• coolers

• cleaning aids such as brushes, sponges, etc.

• product and/or equipment wash areas

• food contact surfaces

• condensate

• walls and ceilings

• compressed air

Control of Listeria relies on detecting and managing harborage sites with thorough and frequent cleaning.

The body's defense against Listeria monocytogenes and other intracellular pathogens is called "cell-mediated immunity" because it depends on our cells (as opposed to our antibodies), especially lymphocytes called "T-cells." Therefore, it is not surprising that individuals whose cell-mediated immunity is suppressed are more susceptible to the devastating effects of Listeriosis. Persons with AIDS suffer listeriosis 65-145 times more frequently than the general population.

Pregnant women naturally have a depressed cell-mediated immune system; many think that this occurs so that the mother's immune system will not reject the fetus. Pregnant women are about 20 times more likely than other healthy adults to contract listeriosis. About one-third of listeriosis cases happen during pregnancy. The incidence of listeriosis in the newborn is 8.6 per 100,000 live births (Tappero et al., 1995). Newborns, rather than the pregnant women themselves, suffer the serious effects of infection in pregnancy.

Symptoms

• Fever

• Muscle aches

• Nausea or diarrhea (sometimes)

If the infection spreads to the nervous system, listeriosis can cause:

• Headache

• Stiff neck

• Confusion

• Loss of balance

• Convulsions

Prevention

• Ready-to-eat foods: Hot dogs, cold cuts, lunchmeats, deli counter meats, and other ready-to-eat foods. Eat these foods only if they're reheated until steaming hot. Even cured meats such as salami must be heated.

• Meats and seafood: Cook these all the way through. Stay away from rare meat and seafood.

• Leftovers: Reheat all until steaming hot.

• Fruits and vegetables: Listeria can grow on some fruits and vegetables. Do not buy sliced melon. Wash all fruits and vegetables with water. Scrub hard produce such as cucumbers and melons with a clean produce brush.

• When you buy pre-cooked or ready-to-eat foods that go in the fridge, use them as soon as you can.

• Clean your fridge often.

• Make sure that the fridge always stays at 40 degrees F or colder. Use a refrigerator thermometer.

• Read labels. Follow instructions on foods that must be kept in the fridge or have a "use by" date.

• Wash your hands with warm soapy water after you touch raw foods. Wash any knives or other tools you used with hot, soapy water before you use them again.

Diagnosis

There is no routine screening test for susceptibility to listeriosis during pregnancy, as there is for rubella and some other congenital infections. The SafePathä Listeria ELISA is a rapid and reliable test, which significantly reduces the time required to screen foods for the presence of Listeria. The assay can detect LM, L. innocua and L. welshimeri. Primary enrichment cultures grown for 24 to 48 hours can be tested in less than one hour, allowing ELISA-negative product to be released sooner than with standard methods. Presumptively positive ELISA samples can be cultured further for confirmation by standard methods.

Treatment

Listeriosis is treated with the antibiotics ampicillin (Omnipen) or sulfamethoxazole-trimethoprim (Bactrim, Septra). Because the bacteria live within macrophage cells, treatment may be difficult and the treatment periods may vary.

http://www.safepath.com/Listeria-96well.php

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