Common Foodborne Pathogens: Listeria monocytogenes

What is Listeria monocytogenes?

Listeria monocytogenes is a bacterium commonly found in soil, water, sewage, and decaying plant material. L. monocytogenes is a particularly hardy pathogen, capable of surviving in damp areas, and on stainless steel and glass within the food processing environment. Once established, it is difficult to eliminate and may often be the cause of post-process food contamination.

Although easily killed by heat; refrigeration does not prevent the growth of this organism. In fact, L. monocytogenes is unique among foodborne pathogens in that it not only survives, but can grow at refrigeration temperatures! Foods most commonly associated with this illness are refrigerated foods that are not reheated before consumption

Who gets Listeria monocytogenes Infection?

Listeriosis is a severe infection c aused by L. monocytogenes. Most healthy persons do not experience symptoms of listeriosis following ingestion of small a mounts of L. monocytogenes. Those at highest risk of developing symptoms include pregnant women, the immunoc ompromised, young children, and the elderly. These populations c an bec ome ill by c onsuming a very small c onc entration.

Symptoms of Listeria monocytogenes Infection

The most c ommon symptoms of listeriosis include a mild flu-like illness with persistent fever, muscle a ches, nausea or diarrhea. If the infection progresses to the nervous system, hea da che, c onfusion, loss of balanc e, and c onvulsions may oc cur. Infection during pregnancy may lea d to misc arriage, stillbirth, early delivery, or infection of the fetus.

Proper Food Handling Techniques to Avoid Infection

Heat rea dy-to-eat foods (i.e. hotdogs, deli meats) and leftovers until they are stea ming hot. Do not c onsume unpasteurized milk or dairy products. Cook all poultry, meats, and seafoo d to c orrect internal temperatures for 15 sec onds. Rinse fruits and vegetables thoroughly with water, especially those that will not be c ooked. Refrigerate or freeze ingredients and leftovers imme diately after use.

Recent Listeriosis Outbreaks in the U.S.

In 2002, a multistate outbreak of 46 culture-c onfirmed c ases, seven deaths, and three stillbirths or misc arriages in eight states was linked to eating slic eable turkey deli meat. One inta ct food product and 25 environmental sa mples from a poultry proc essing plant yielded L. monocytogenes. Two environmental isolates from floor drains were indistinguishable from that of outbreak patient isolates, suggesting that the plant might have been the sourc e of the outbreak. Increased plant sanitation, or c ooking the deli meat before c onsumption may have prevented the outbreak.

Commonly Associated Foods

• Ready-to- eat foods (i.e. hot dogs, deli meats)

• Unpasteurized dairy products

• Raw fruits and vegetables

• Refrigerated pâtés, meat spreads and smoked seafood

Safe Food Handling Checklist

• Heat ready-to eat foods (hot dogs, deli meat) until steaming hot (Important for high risk populations)

• Wash fruits and vegetables with water

• Refrigerate / Freeze ingredients and leftovers after use

• Cook raw meats, poultry, and seafood to correct internal temperatures

Poultry = 165°F
Ground Beef = 160ºF
Fresh Pork = 160°F
Seafood, Steak = 145ºF

For More Information Contact: 

Renee R. Boyer, Ph.D.
Extension Specialist
rrboyer@vt.edu