Internalization of Listeria monocytogenes by nonprofessional and professional phagocytes.

Abstract

Listeria monocytogenes was originally described by Murray et al. (1926), who named it Bacterium monocytogenes due to the characteristic monocytosis found in the blood of experimentally infected animals. In 1940 it was renamed into its present name. L. monocytogenes is a gram-positive, rod-shaped, non-spore forming, facultative anaerobic bacillus which grows in a wide range of temperatures. L. monocytogenes is catalase positive, oxidase negative, CAMP positive, and expresses a hemolysin producing characteristic zones of lysis on blood agar plates. L. monocytogenes is motile when grown between 20 and 25°C, but the synthesis of flagellin is repressed at 37°C and the bacteria are then nonmotile. The cell wall of L. monocytogenes contains peptidoglycan, teichoic acid, and lipoteichoic acid and shows all the charateristics of a typical gram-positive cell wall. While the teichoic acids are covalently linked to the peptidoglycan, the lipoteichoic acids are anchored to the cytoplasmic membrane via a glycolipid moiety. L. monocytogenes is wide spread in nature and is found on plants, in soil, and in freshwater, but also in silage, wastewater, and in human and animal feces (reviewed in Schuchat et al., 1991).