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''L. monocytogenes'' is haemolytic on blood agar due to a cytolytic protein, listeriolysin and grows at range of pH values and temperatures.''L. ivanovii'' produces a strong haemolytic zone. Listeria produces small, smooth, transparent colonies after 24 hours incubation. They are able to grow on non-enriched media.

''L. monocytogenes'' is haemolytic on blood agar due to a cytolytic protein, listeriolysin and grows at range of pH values and temperatures.''L. ivanovii'' produces a strong haemolytic zone. Listeria produces small, smooth, transparent colonies after 24 hours incubation. They are able to grow on non-enriched media.

===Pathogenesis and pathogenicity===

==Pathogenesis and pathogenicity==

*Infection by ingestion of contaminated feed

Listeria cause infection by ingestion of contaminated feed. The bacteria penetrate M cells in intestinal Peyer's patches and spread to tissues via blood and lymph. Transplacental transmission can also occur in pregnant animals.

*Bacteria penetrate M cells in intestinal Peyer's patches

The bacteria may gain entry via breaks in oral or nasal mucosa and migrate in cranial nerves to cause neural signs. This can cause the formation of microabscesses and perivascular lymphocytic cuffs in the brainstem.

*Spread to tissues via blood and lymph

''L. monocytogenes'' can replicate within phagocytic and non-phagocytic cells, and pass between cells without being exposed to the immune system.

*Transplacental transmission in pregnant animals

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. In the cytoplasm, Listeria are motile.

*Bacteria may gain entry via breaks in oral or nasal mucosa, migrate in cranial nerves to cause neural signs

The bacteria can then induce formation of pseudopod projections in the cytoplasmic membrane, which are taken up with the bacteria into adjacent cells.

*Causes formation of microabscesses and perivascular lymphocytic cuffs in brainstem

A cell-mediated immune response is required for protection.

*''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

*Cell-mediated immune response required for protection

===Diagnosis===

==Diagnosis==

*Specimens should include CSF in neural cases, cotyledons in abortion, liver, spleen and blood in septicaemia

*Specimens should include CSF in neural cases, cotyledons in abortion, liver, spleen and blood in septicaemia