Listeria species
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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