https://en.wikivet.net/api.php?action=feedcontributions&feedformat=atom&user=0607215b 2026-07-23T18:56:46Z User contributions MediaWiki 1.35.0 https://en.wikivet.net/index.php?title=Listeria_species&diff=41585 2008-12-04T11:33:33Z

<p>0607215b: /* Characteristics */</p> <hr /> <div>{{review}}<br /> <br /> {{toplink<br /> |backcolour =<br /> |linkpage =Bacteria<br /> |linktext =BACTERIA<br /> |pagetype=Bugs<br /> }}<br /> &lt;br&gt;<br /> ===Overview===<br /> <br /> *6 species<br /> *Saprophytes in soil<br /> *''L. monocytogenes'' and ''L. ivanovii'' are pathogens<br /> *Carried by sheep and goats and shed in faeces and milk especially during stress<br /> *Can cause septicaemia, encephalitis, abortion and endophthalmitis in ruminants<br /> *Outbreaks of listeriosis often linked to silage feeding<br /> *Occurs in North and East Europe and North America<br /> <br /> <br /> ===Characteristics===<br /> <br /> *Small Gram positive rods<br /> *Catalase positive, oxidase negative<br /> *Tumbling motility<br /> *Facultative anaerobes<br /> *Intracellular pathogens<br /> *''L. monocytogenes is haemolytic on blood agar due to a cytolytic protein, listeriolysin; grows at range of pH values and temperatures<br /> *''L. ivanovii produces strong haemolytic zone<br /> *Small, smooth, transparent colonies after 24 hours incubation<br /> *Grow on non-enriched media<br /> <br /> ===Pathogenesis and pathogenicity===<br /> <br /> *Infection by ingestion of contaminated feed<br /> *Bacteria penetrate M cells in intestinal Peyer's patches<br /> *Spread to tissues via blood and lymph<br /> *Transplacental transmission in pregnant animals<br /> *Bacteria may gain entry via breaks in oral or nasal mucosa, migrate in cranial nerves to cause neural signs<br /> *Causes formation of microabscesses and perivascular lymphocytic cuffs in brainstem<br /> *''L. monocytogenes'' can replicate within phagocytic and non-phagocytic cell, and pass between cells without being exposed to the immune system<br /> *Surface proteins known as internalins allow adherence and uptake of the bacteria into cells<br /> *Listeriolysin produced by virulent strains destroys membranes of phagocytic vacuoles, releasing the bacteria into the cytoplasm<br /> *Listeria are motile in the cytoplasm <br /> *Bacteria induce formation of pseudopod projections in the cytoplasmic membrane, which are taken up with the bacteria into adjacent cells<br /> *Cell-mediated immune response required for protection<br /> <br /> <br /> ===Clinical infections===<br /> <br /> *Outbreaks of listeriosis caused by ''L. moncytogenes'' seasonal and linked to silage feeding<br /> *Replicates in poor quality silage where the pH excedes 5.5<br /> *Animals highly susceptible during pregnancy due to lowered cell-mediated immunity<br /> *Neural listeriosis:<br /> **Incubation period 14-40 days<br /> **Meningoencephalitis<br /> **Dullness, circling, head tilt, facial paralysis, drool saliva, droop of eyelid and ear<br /> **Exposure keratitis<br /> **Fever during early stages<br /> **Recumbency and death within a few days in sheep and goats<br /> **Abortion up to 12 days after infection in cattle; usually recover but may get septicaemia<br /> *Septicaemic listeriosis:<br /> **Incubation perios 2-3 days<br /> **Lambs and occasionally pregnant sheep<br /> **Occurs in newborn piglets, foals, poultry, adult sheep<br /> *Keratoconjunctivitis in cattle and sheep - direct contact with silage via eye<br /> *Pneumonia, myocarditis, enodcarditis<br /> *Zoonosis - consumption of contaminated unpasteurised milk; memingitis and meningoencephalitis; abortion<br /> <br /> *''L. ivanovii causes sporadic abortion in sheep and cattle<br /> *''L. innocua'' rarely causes ovine meningoencephalitis<br /> <br /> <br /> ===Diagnosis===<br /> <br /> *Specimens should include CSF in neural cases, cotyledons in abortion, liver, spleen and blood in septicaemia<br /> *Immunofluorescence using monoclonal antibodies<br /> *Histology of brain demonstrates microabscesses and lymphocytic cuffing in brainstem<br /> *Smears of cotyledons<br /> *High protein and cell counts in CSF<br /> *Isolation on blood and MacConkey agar<br /> <br /> <br /> ===Treatment and control===<br /> <br /> *Ampicillin or amoxycillin in early stages of septicaemic listeriosis<br /> *Sub-conjuntival antibiotics and corticosteroids for ocular listeriosis<br /> *Avoid poor quality silage and discontinue silage-feeding in an outbreak</div>

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