Listeria Monocytogenes: An Overview of the Disease Causing Bacteria

Listeriosis is a food borne illness caused by bacteria (Listeria monocytogenes) that thrive in cold environments. Listeria monocytogenes is found in animal intestines, as well as in soil, water, and plants.

What exactly is Listeria Monocytogenes?

Listeria monocytogenes is a type of bacteria that can be found in soil and water. Animals carry it without becoming ill, contaminating animal-derived foods such as meat and dairy products. This organism can contaminate vegetables grown in soil fertilized with tainted manure.

Who is susceptible to listeriosis?

Anyone can get the disease, but pregnant women, the elderly, people with weakened immune systems (for example, people with cancer, HIV/AIDS, or a transplant), and people with chronic liver or kidney disease, diabetes, or alcoholism are at higher risk.

When healthy adults and children become infected with Listeria, they rarely become seriously ill. Although the majority of cases are isolated incidents, food-borne outbreaks (when two or more people become ill from the same source) do occur.

Which foods are the most frequently contaminated with Listeria monocytogenes?

Animal foods are the most contaminated by listeria monocytogenes; examples of such foods include:

  1. Unpasteurized milk
  2. Listeria monocytogenes can be found in soft cheeses such as feta and brie, as well as raw vegetables.
  3. Poultry, meats (including hot dogs and lunch meat), and ready-to-eat prepared, chilled foods are also at risk.
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How is Listeria Monocytogenes killed?

Listeria monocytogenes can only be killed by the action of heat on food.

Listeria is killed by pasteurization and heat used in the preparation of ready-to-eat processed meats.

Contamination can, however, occur after processing. Listeria multiplies and grows at refrigeration temperatures every day the contaminated product is stored.

What are the signs and symptoms of listeriosis?

If you get a listeria infection, you could have

  1. Fever
  2. Chills
  3. Muscle aches
  4. Nausea
  5. Diarrhea
  6. Vomiting

Symptoms may appear a few days after eating contaminated food, but it may take 30 days or more for the first signs and symptoms of infection to appear.

If the listeria infection spreads to your nervous system, you may experience the following signs and symptoms:

  1. Headache
  2. Stiff neck
  3. Confusion or changes in alertness
  4. Loss of balance
  5. Convulsions
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Listeria monocytogenes typically causes a flu-like illness with fever and chills in pregnant women.

Complications of Listeria Monocytogenes

The majority of listeria infections are so mild that they go unnoticed. In some cases, however, a listeria infection can result in life-threatening complications, such as:

  1. Generalized blood infection
  2. Inflammation of the membranes and fluid that surround the brain (meningitis)

How is Listeria monocytogenes identified?

Only specific laboratory tests can be used to diagnose this disease. If the disease is present, a blood, spinal fluid, or amniotic fluid/placenta test that looks for bacteria will be able to detect it.

What is the cure for listeriosis?

Antibiotics are used to treat listeriosis. Ampicillin can be used alone or in conjunction with other antibiotics.


To avoid a listeria infection, you must do the following:

  1. Maintain a clean environment.
  2. Thoroughly wash your hands with warm, soapy water before and after handling or preparing food.
  3. Cook your food completely.
  4. Make sure your meat, poultry, and egg dishes are cooked to a safe temperature by using a food thermometer.
  5. Cook raw animal foods such as beef, pork, or poultry to the proper temperature. 145 degrees Fahrenheit for whole meats, plus 3 minutes of stand time for safety. No stand time is required for ground meats at 160°F. 165 degrees Fahrenheit for all poultry, whether ground or whole.
  6. Before eating raw vegetables, thoroughly wash them.
  7. Separate the uncooked meats from the vegetables, cooked foods, and ready-to-eat foods.
  8. After cooking,make sure to wash the utensils, cutting boards, and other food preparation surfaces with hot, soapy water.
  9. Clean raw vegetables.
  10. Under running water, scrub raw vegetables with a scrub brush or vegetable brush.
  11. Unpasteurized (raw) milk and foods made from unpasteurized milk should be avoided.
  12. Perishable and ready-to-eat foods should be consumed as quickly as possible.
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