Listeria monocytogenes is a small rod shaped gram-positive bacterium that is ubiquitous in the environment, in the soil, on plants and animals. Listeriosis (the state of Listeria infection) is associated with eating of unpasteurized cheese or dairy products, or consumption of contaminated vegetables. Infection occurs primarily in newborns and infants, elderly or immunocompromised individuals, or pregnant women (mother is asymptomatic or has influenza-like syndrome, but the newborn can acquire it during birth, or infection can cause abortion or premature delivery). According to the CDC about 1500 cases are reported in the United States each year, mostly in the aforementioned high risk groups.
Listeria enters the host along with infected food. Most of the bacteria will be killed by acid in the stomach, but the surviving bacteria invade the cells of the intestinal tract, going from cell to cell and thereby spreading the infection laterally. Intracellular movement of the bacteria is essential for this lateral infection to occur, and Listeria has been described to move with a "comet-tail" or like an "actin rocket". The Theriot Laboratory is studying how Listeria moves within cells, and results of this research may someday be used to generate vaccines or other means to prevent infection by Listeria. Currently, the only preventive measures are thorough cooking and cleaning of food, as well as pasteurization of dairy products. Treatment of Listeriosis primarly depends on antibiotics. (medical information from Medical Microbiology & Immunology, by Levinson and Jawetz, 5th Edition)
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