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<big><center>[[Infectious agents and parasites|'''BACK TO INFECTIOUS AGENTS AND PARASITES''']]</center></big>
<big><center>[[Infectious agents and parasites|'''BACK TO INFECTIOUS AGENTS AND PARASITES''']]</center></big>
<big><center>[[Bacteria|'''BACK TO BACTERIA''']]</center></big>
<big><center>[[Bacteria|'''BACK TO BACTERIA''']]</center></big>
===Overview===
*6 species
*Saprophytes in soil
*''L. monocytogenes'' and ''L. ivanovii'' are pathogens
*Carried by sheep and goats and shed in faeces and milk especially during stress
*Can cause septicaemia, encephalitis and abortion
===Characteristics===
*Small Gram negative rods
*Catalase positive, oxidase negative
*Motile
*Facultative anaerobes
*''L. monocytogenes is haemolytic on blood agar due to a cytolytic protein, listeriolysin; grows at range of pH values and temperatures
*''L. ivanovii produces strong haemolytic zone
*Small, smooth, transparent colonies after 24 hours incubation
===Pathogenesis and pathogenicity===
*Infection by ingestion of contaminated feed
*Bacteria penetrate M cells in intestinal Peyer's patches
*Spread to tissues via blood and lymph
*Transplacental transmission in pregnant animals
*Bacteria may gain entry via breaks in oral or nasal mucosa, migrate in cranial nerves to cause neural signs