| dc.description.abstract | Listeria are glam positive non-spong rods that were found in diverse environments including water, seafood, dairy products and vegetables. Outbreaks of listeriosis due to the consumption of foods contaminated L.monocytogenes, coupled with the high mortality rate and the nsk posed to immuno compromised individuals have resulted in more focus being placed on Listeria-free products. Although most recorded Listeria outbreaks have been linked to contaminated food, most of these foods have a previous history of soil and / or water contact but little is known regarding its prevalence in soil and water. The aim of the work reported here was to ascertain the prevaluice and diversity of Listeria and bacteria that could be regarded as Listeria in various foods and in natural and irrigation waters in order to develop a reliable and conclusive detection method. Various methods including conventional culturing selective techniques, immunological methods and a variety of polymerase cham reaction methods have been developed for the detection of Listeria. In this study, preminary physiological tests were utilized to detect Listeria from 108 natural and irrigation water samples, 34 dairy samples, 33 raw and processed fish samples and 30 vegetable samples. After these preliminary tests, one-hundred and twelve isolates were found to be gram positive non-sporing rods that could hydrolyse aescuhn. These isolates were further tested using both genotypical (PCR with primers directed at the 165 rRNA gene and the invasive associated protein gene ) and phenotypical (BIOLOG and whole-cell protein analysis). The whole protein profiles divided the various isolates into two main divisions namely, Listeria and ListeriaJike organisms. A diverse selection of Listeria and, Listerio-like strarns, some of which are very distant from currently accepted members of the genus, were isolated. Dalry products (especially soft cheeses), seafoods and water isolates clustered in separate niches within the Listeria division. The majority of vegetables, however, were mainly contaminated by Listeria-like organisms and not true Listeria. The presence of these Listeria in a Iocal river was of some concernsince the local children used the river as a swimming facility. Some isolates from the river, although related to the type strains, were separate from typical Listeria. Thus, the possibility exists that this group could be a new species or subspecies. The development of a l65 rDNA primer set (CLis2 and CLis4) for the detection is reported. All isolates that contained the invasive associated protein (iap) gene resulted in a PCR product of l.5kb and those that contained the 165 rRNA gene resulted in a product of 0.68kb Although these primer sets could detect most Listeria, they could not
detect all. The development of more selective media for the preliminary detection of Listeria and the reduction in the number of physiologrcal tests, were recommended as well as the optimisation of the l65 rRNA PCR for the direct detection of Listeria rn food products. | en_US |
