Listeria is a widely distributed bacterium and has been found in food manufacturing plants with a higher incidence in seafood, fresh vegetables, and raw milk containing foods. The bacterium is found in the normal flora of the GI tracts of cattle, sheep, poultry, birds, fish, insects, cats and dogs. It is excreted in the fecal material and has been found in samples of soil, stale water supplies, silage, dust, animal hides and manure. It can also be transferred from these sources to plants and contaminate fresh produce. Listeria is deadlier than well-known pathogens like Salmonella and E. coli, though those outbreaks generally cause many more illnesses.  It is a bacterium from the  the family Listeriaceae and can cause  listeriosis  infection.  Listeriosis is a potentially fatal illness among the elderly, the very young and those with compromised immune systems. Listeriosis is an illness usually caused by the consumption of food contaminated with Listeria monocytogenes bacteria. In healthy people, listeriosis may have few or no symptoms. In individuals at particular risk (pregnant women, the elderly) symptoms may include headache, fever, aches, pains and tiredness. The illness may also progress to a more serious form, such as meningitis (brain infection) and septicaemia (blood poisoning). In some cases, the listeria infection can be serious enough to be a threat to life.

Listeria can also cause serious spontaneous abortion in pregnant women and therefore it is dangerous to pregnant women.

Listeria is a facultative intracellular parasite.  It can infect a large number of possible mammalian hosts, in addition to birds, insects, and crustaceans.  It is killed by cooking, but it can grow and multiply in refrigerators.  Listeria is killed quite easily by heating or pasteurization.

Listeria has a widely variable incubation period, from case to case and from person to person.  It has a predilection for the placenta and central nervous system.  It can readily invade the placenta and
precipitate premature labor and fetal death.

Listeria can grow in the fridge — unless it is 4 degrees Celcius or below.  It is sensitive to antimicrobial therapy and resistance to the most commonly used drugs appears to be rare.  It can live for quite a long time on an inanimate object.  It cannot be seen and it does not change the way the food looks, so always play it safe.

The species well known to cause food poisoning is Listeria monocytogenes. Listeria monocytogenes is a hardy bacterium which has several unique survival characteristics compared to other microorganisms that cause foodborne disease.  Listeria  is widely distributed in nature.