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Evaluation of Diagnostic PCR for the Detection of Listeria monocytogenes in Food Products

Pieter A. Gouws* and Ilse Liedemann


Department of Biotechnology, University of the Western Cape, Private Bag X 17, Bellville 7535, South Africa

Article history:

Received July 27, 2004
Accepted February 28, 2005

Key words:

Listeria monocytogenes, PCR, diagnostic, food products

Summary:

Conventional methods for the detection of Listeria in foodstuffs are generally cumbersome and time consuming. The use of primary enrichment in ½ strength Fraser broth and the use of Oxford and RAPID’L. mono agars were assessed in comparison with polymerase chain reaction (PCR) for their ability to accurately detect and confirm the presence of L. monocytogenes in food products. Of the 27 food samples tested, 74 % were presumptively positive for Listeria on Oxford agar, while 44 % were presumptively positive for L. monocytogenes on RAPID’L. mono. Only 37 % of samples were confirmed to be positive for L. monocytogenes by PCR amplification of the hly gene (732 bp). PCR was able to eliminate the false positives and detect all L. monocytogenes in the food products, unlike the conventional methods used in the industry. In addition to the fact that the incidence of Listeria species was higher than L. monocytogenes on selective media, there was also the presence of Listeria-like organisms. These organisms had the typical appearance of Listeria on selective media, but were non-Listeria species, as confirmed by the PCR and API Listeria (bio- Mérieux). PCR proves to be a sensitive and rapid technique to be included in the procedure of detection of L. monocytogenes in food products.



*Corresponding author:     pgouws@uwc.ac.za
                                         ++27 21 959 35 05

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