Listeria : For the disease caused by Listeria see Listeriosis

Listeriosis is a bacterial infection caused by a Gram-positive, motile bacterium, Listeria monocytogenes.^[1] Listeriosis is relatively rare and occurs primarily in newborn infants, elderly patients, and patients who are immunocompromised.^[2]
The symptoms of listeriosis usually last 7–10 days, with the most common symptoms being fever, muscle aches, and vomiting. Diarrhea is another, but less common symptom. If the infection spreads to the nervous system it can cause meningitis, an infection of the covering of the brain and spinal cord. Symptoms of meningitis are headache, stiff neck, confusion, loss of balance, and convulsions.
Listeriosis has a very low incidence in humans. However, pregnant women are much more likely than the rest of the population to contract it. Infected pregnant women may have only mild, flulike symptoms. However, infection in a pregnant woman can lead to early delivery, infection of the newborn, and death of the baby.^[3] It seems that Listeria originally evolved to invade membranes of the intestines, as an intracellular infection, and developed a chemical mechanism to do so. This involves a bacterial protein " internalin" which attaches to a protein on the intestinal cell membrane " cadherin." These adhesion molecules are also to be found in two other unusually tough barriers in humans - the blood brain barrier and the feto - placental barrier, and this may explain the apparent affinity that Listeria has for causing meningitis and affecting babies in-utero.
In veterinary medicine, listeriosis can be a quite common condition in some farm outbreaks. It can also be found in wild animals; see listeriosis in animals.