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Listeria monocytogenes

Photomicrograph of listeria monocytogenes

Electron micrograph of listeria monocytogenes

Pathogens & Protocols

Why it's a Threat

This pathogen causes nearly 2,500 cases of listeriosis per year in the United States. It primarily affects pregnant women, newborns, and adults with weakened immune systems.


Gram-positive bacteria, found as single short rods or chains approximately 0.5 micron wide and 1 micron long. Listeria may swim with 1-5 flagella to invade human cells.


Cold and/or wet places including refrigeration and air handling systems; thrives in dairy products including soft cheeses, deli meats, hotdogs, and food processing plants.


  • Cook raw food from animal sources, such as beef, pork, or poultry to a safe internal temperature. For a list of recommended temperatures for meat and poultry, visit's safe minimum cooking temperatures chart web page.
  • Use precooked or ready-to-eat food as soon as you can. Do not store the product in the refrigerator beyond the use-by date.
  • Do not drink raw (unpasteurized) milk, and do not eat foods that have unpasteurized milk in them.More


Although harmless in most healthy people, listeriosis poses a serious threat to pregnant women, newborns, and individuals with weakened immune systems.

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