Listeria monocytogenes is a gram-positive rod-shaped bacterium. It is the causative agent of listeriosis, a serious infection caused by eating food contaminated with the bacteria. The disease generally affects older adults, pregnant women, newborns, and adults with weakened immune systems, however, rarely, persons without these risk factors are also infected  
The overt form of the disease has mortality greater than 25 percent. The two main clinical manifestations are sepsis and meningitis. Meningitis is often complicated by encephalitis, a pathology that is unusual for bacterial infections .
Golnazarian et al.(1989) compared infectious dose in normal and compromised C57BL/6J mice with pathogens (strain F5817) via oral route and responses were recorded as death and infection separately. Audurier et al.(1980)  conducted an experiment on Swiss female mice (OF1) via oral route and infection was observed after 28 days of inoculation.The dose-response analysis of both cases were published by Haas, Thayyar-Madabusi in 1999