Abstract:
From a public health standpoint, it is extremely important to
identify the contaminated food vehicle and remove it from food distribution
channels as rapidly as possible. A rapid PCR method was developed for early
detection and molecular serotyping of L. monocytogenes in dairy products. This
method includes Modified DNA extraction procedure to remove the PCR
inhibitors and followed by a nested PCR to increase the sensitivity of the
detection. This method of detection was found to be more reliable and easy
to perform compare to the conventional method thus would reduce
additional morbidity and mortality of human cases of listeriosis. Outbreak
investigations offer unique opportunities to identify the source of
contamination of implicated foods, to learn more about the transmission of L.
monocytogenes in humans, and to identify measures to prevent future cases and
in view of this raw milk, pasteurized milk, Ice cream, curd, yoghurt and
cheese samples were collected randomly from many parts of the country and
tested by PCR for the presence of L. monocytogenes. Out of 266 samples, 78
became positives in which the highest number of L. monocytogenes (42%)
detected from raw milk. This number (42%) is higher in comparison to other
countries, which indicate hygienic conditions of milking, and the subsequent
manipulations in the production line of the milk products are substandard in
our country. Out of the total strains detected by PCR 61.51%, 11.53% and 4%
belong to serotypes ½a, ½b and ½c, respectively. Most of these raw milk
isolates represented serotypes (½a and ½b) previously been linked to
multiple human listeriosis outbreaks. These results indicate the seriousness
of the L. monocytogenes contamination in the dairy industry in Sri Lanka
alarming the concerned authorities to take appropriate remedial measures to
keep the situation under control. The nested PCR method developed here is
cost effective and suitable for developing counties. First time in Sri Lanka the
serotypes ½a and ½b circulating in the country were identified from the
dairy products representing different parts of the country. This opens the
avenue for more research on identifying more serotypes in circulation and to
trace their lineage.
