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Listeria is a genus of bacteria that, until 1992, contained 10 known species,[1][2] each containing two subspecies. As of 2014, another five species were identified.[3] Named after the British pioneer of sterile surgery Joseph Lister, the genus received its current name in 1940. Listeria specie
The first documented case of listeriosis was in 1924. In the late 1920s, two researchers independently identified L. monocytogenes from animal outbreaks. They proposed the genus Listerella in honor of surgeon and early antiseptic advocate Joseph Lister, but that name was already in use for a slime mold and a protozoan. Eventually, the genus Listeria was proposed and accepted. All species within the genus Listeria are Gram-positive, catalase-positive rods and do not produce endospores. The genus Listeria was classified in the family Corynebacteriaceae through the seventh edition of Bergey's Manual of Systematic Bacteriology. The 16S rRNA cataloging studies of Stackebrandt, et al. demonstrated that L. monocytogenes is a distinct taxon within the Lactobacillus-Bacillus branch of the bacterial phylogeny constructed by Woese. In 2004, the genus was placed in the newly created family Listeriaceae. The only other genus in the family is Brochothrix.[7]The genus Listeria currently contains 17 species: L. aquatica, L. booriae, L. cornellensis, L. fleischmannii, L. floridensis, L. grandensis, L. grayi, L. innocua, L. ivanovii, L. marthii, L. monocytogenes, L. newyorkensis, L. riparia, L. rocourtiae, L. seeligeri, L. weihenstephanensis, and L. welshimeri.[8] Listeria dinitrificans, previously thought to be part of the genus Listeria, was reclassified into the new genus Jonesia.[9] Under the microscope, Listeria species appear as small rods, which are sometimes arranged in short chains. In direct smears, they may be coccoid, so they can be mistaken for streptococci. Longer cells may resemble corynebacteria. Flagella are produced at room temperature, but not at 37 °C. Hemolytic activity on blood agar has been used as a marker to distinguish L. monocytogenes from other Listeria species, but it is not an absolutely definitive criterion. Further biochemical characterization may be necessary to distinguish between the different species of Listeria.