an epidemiological study of listeriosis in dairy cattle

CHAPTER 5
A pilot study of the bacteriological and serological techniques
used to determine the infection of cows with Listeria
5. 1. Introduction:
monocytogenes
Sensitive techniques for the isolation and identification of L. monocytogenes are
essential for the diagnosis of outbreaks and sporadic cases of Listeriosis. They are
also important in epidemiological investigations and in assessing the bacteriological
safety of food.
Listeria grow well on most of the commonly used bacteriological culture media
after initial isolation (Gray and Killinger 1966). However initial isolation from
contaminated materials has always been challenging (Murray and others 1926, Farber
and Peterkin 1991). This difficulty stimulated a search for more selective methods of
isolation which was also fuelled by the increasing number of outbreaks of Listeriosis
in people associated with the consumption of food contaminated with L.
monocytogenes. The aim of these developments was to detect small numbers of L.
monocytogenes, in a shorter period of time and also to increase the probability of
recovering injured organisms (Buchanan, 1990). Several techniques were employed;
direct plating on selective and non-selective agar and the use of selective and non-
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