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an epidemiological study of listeriosis in dairy cattle

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growth <strong>of</strong> some stra<strong>in</strong>s <strong>of</strong> Listeria (Seeliger <strong>an</strong>d Jones 1986, Curtis <strong>an</strong>d other 1989b).<br />

To obta<strong>in</strong> maximum success <strong>in</strong> isolation <strong>of</strong> Listeria a three stage procedure was<br />

recommended (Curtis <strong>an</strong>d Lee 1995); (a) resuscitation or pre-enrichment (selective or<br />

non-selective) (b) selective enrichment <strong>an</strong>d (c) selective plat<strong>in</strong>g. This procedure has<br />

been used to isolate Listeria from food (Lewis <strong>an</strong>d Cory 1991, McLa<strong>in</strong> <strong>an</strong>d Lee,<br />

USDA method, 1988), sewage (Watk<strong>in</strong>s <strong>an</strong>d Sleath 1981), cl<strong>in</strong>ical samples (Eld <strong>an</strong>d<br />

others 1993) <strong>an</strong>d environmental samples (Fenlon 1985, Husu 1990).<br />

The difficulty <strong>in</strong> isolat<strong>in</strong>g L. monocytogenes me<strong>an</strong>s that bacteriological methods<br />

are not always satisfactory when attempt<strong>in</strong>g to determ<strong>in</strong>e the exposure <strong>of</strong> <strong>an</strong>imals to<br />

Listeria org<strong>an</strong>isms (Gray <strong>an</strong>d Kill<strong>in</strong>ger 1966) <strong>an</strong>d serological techniques have been<br />

used as supplementary tools for this purpose. Specific ELISA tests, employ<strong>in</strong>g cell<br />

products <strong>in</strong>volved <strong>in</strong> pathogenesis such as listeriolys<strong>in</strong> O, have been used <strong>in</strong><br />

experimental studies. No large scale use <strong>of</strong> these ELISA assays, <strong>in</strong>volv<strong>in</strong>g field studies<br />

has, yet been conducted (Berche <strong>an</strong>d others 1990, Low <strong>an</strong>d Donachie 1991, Low <strong>an</strong>d<br />

others 1992b, Gholizadeh <strong>an</strong>d others 1996).<br />

A pilot <strong>study</strong> <strong>in</strong>volv<strong>in</strong>g a <strong>dairy</strong> herd was carried out to develop <strong>an</strong>d st<strong>an</strong>dardise<br />

bacteriological <strong>an</strong>d serological techniques which would be used <strong>in</strong> a longitud<strong>in</strong>al<br />

survey <strong>of</strong> L. monocytogenes <strong>in</strong>fection.<br />

5. 2. Materials <strong>an</strong>d methods<br />

132

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