Anatomy of a pathogen: Listeria

Listeria is a common family of bacteria that can be found in the soil, water and even in some animals (including poultry and cattle). One member of the Listeria family is one of the major foodborne pathogens—alongside Salmonella and E. coli 0157:H7—and also one of the more dangerous ones, as it can survive not only in normal, ambient temperatures, but in cold temperatures as well.

Today, we will be focusing on what exactly this pathogen is—and how to best avoid getting a foodborne illness from it.

What is the difference between Listeria and Listeria monocytogenes?

Listeria monocytogenes is a specific strain of Listeria. According to the U.S. Food and Drug Administration (FDA), at least 37 mammalian species, 17 species of birds, 1–10% of humans and potentially even some species of fish and shellfish may be carriers of the pathogen. Like all Listeria, L. monocytogenes can defend itself quite well against both hot and cold conditions.

Where is L. monocytogenes most commonly found?

It is found in ready-to-eat deli meats or hot dogs (learn more about food safety of hot dogs here). Listeria can also be found in refrigerated pâtés, meat spreads and smoked seafood; products made with unpasteurized or raw milk, such as queso fresco and brie; and raw sprouts.

What is listeriosis?

Here’s an easy explanation: there is a pathogen called L. monocytogenes. It is very bad. Listeriosis is the name of disorders associated with L. monocytogenes.

Now that we have all of that covered: What is the basic history?

There is some discrepancy as to the exact year the pathogen was discovered, but it was first discovered sometime around the 1920s (see different dates here, here and here), and discovered as a pathogen known to infect humans sometime later. In the 1980s, it was recognized as a foodborne pathogen.

Originally upon its discovery, the pathogen was called Bacterium monocytogenes, and was later named into the genus Listeria in 1940.

What are the symptoms?

Listeriosis is usually accompanied by fever, muscle aches, diarrhea and/or other gastrointestinal symptoms—although symptoms may not be the same across all individuals. Those who are pregnant may experience a fever, aches, fetal loss or other harm to their newborns (such a meningitis). Older individuals, or those with compromised immune systems, may also experience gastroenteritis or no symptoms at all.

If you become sick with a fever, muscle aches or a stiff neck, especially while pregnant, consult your doctor. They may perform a blood or a spinal fluid test to look for the bacteria.

Should it be confirmed that you have listeriosis, the disease is treated with antibiotics. Pregnant women, older adults and anyone with a  weakened immune system who “experiences a fever with other non-specific symptoms, such as fatigue and aches, within two months of eating contaminated foor should seek medical care and tell [their physician] about eating the contaminated food,” according to the Centers for Disease Control and Prevention.

In some cases, listeriosis can result in death.

How can I prevent it?

In general, keep a clean kitchen environment. Rinse all raw fruit and vegetable products before cutting, cooking or eating. Separate raw meat products from other food items (and use separate cutting boards, knives and utensils for these items, if possible). Wash your hands often with warm, soapy water when cooking, and be sure to keep all countertops clean as well.

Remember that Listeria can also survive, and thrive, in the refrigerator. Use a refrigerator thermometer to ensure it is kept at a temperature of 40°F or lower; your freezer should be kept at 0°F or lower.

In addition, cook foods properly and thoroughly (for more information, click here), and be sure to store your foods safely.

Pregnant women are advised to not eat hot dogs, smoked seafood, lunch or deli meats unless they are reheated and steaming hot. Pregnant women should also not eat soft cheeses, pâté or meat spreads. For more information on prevention practices, click here.

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