Difference between revisions of "Listeria species"
Jump to navigation
Jump to search
| Line 9: | Line 9: | ||
*Carried by sheep and goats and shed in faeces and milk especially during stress | *Carried by sheep and goats and shed in faeces and milk especially during stress | ||
*Can cause septicaemia, encephalitis and abortion | *Can cause septicaemia, encephalitis and abortion | ||
| + | *Outbreaks of listeriosis often linked to silage feeding | ||
| Line 20: | Line 21: | ||
*''L. ivanovii produces strong haemolytic zone | *''L. ivanovii produces strong haemolytic zone | ||
*Small, smooth, transparent colonies after 24 hours incubation | *Small, smooth, transparent colonies after 24 hours incubation | ||
| + | *Grow on non-enriched media | ||
| Line 29: | Line 31: | ||
*Transplacental transmission in pregnant animals | *Transplacental transmission in pregnant animals | ||
*Bacteria may gain entry via breaks in oral or nasal mucosa, migrate in cranial nerves to cause neural signs | *Bacteria may gain entry via breaks in oral or nasal mucosa, migrate in cranial nerves to cause neural signs | ||
| + | *Causes formation of microabscesses and perivascular lymphocytic cuffs in brainstem | ||
| + | *''L. monocytogenes'' can replicate within phagocytic and non-phagocytic cell, and pass between cells without being exposed to the immune system | ||
| + | *Surface proteins known as internalins allow adherence and uptake of the bacteria into cells | ||
| + | *Listeriolysin produced by virulent strains destroys membranes of phagocytic vacuoles, releasing the bacteria into the cytoplasm | ||
| + | *Listeria are motile in the cytoplasm | ||
| + | *Bacteria induce formation of pseudopod projections in the cytoplasmic membrane, which are taken up with the bacteria into adjacent cells | ||
| + | |||
| + | |||
| + | ===Clinical infections=== | ||
Revision as of 07:12, 20 July 2008
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
- Outbreaks of listeriosis often linked to silage feeding
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
- Grow on non-enriched media
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
- Causes formation of microabscesses and perivascular lymphocytic cuffs in brainstem
- L. monocytogenes can replicate within phagocytic and non-phagocytic cell, and pass between cells without being exposed to the immune system
- Surface proteins known as internalins allow adherence and uptake of the bacteria into cells
- Listeriolysin produced by virulent strains destroys membranes of phagocytic vacuoles, releasing the bacteria into the cytoplasm
- Listeria are motile in the cytoplasm
- Bacteria induce formation of pseudopod projections in the cytoplasmic membrane, which are taken up with the bacteria into adjacent cells