Abstract

ARIAS, María Laura; CHAVES, Carolina  and  SOLANO, Gabriela. Evaluation of the polymerase chain reaction (PCR) for the detection and identification of Listeria monocytogens in fresh cheese coming from the Metropolitan Area of San José, Costa Rica. ALAN [online]. 2010, vol.60, n.4, pp.391-396. ISSN 0004-0622.

Food borne diseases are very important worldwide and their frequency is still high despite the different efforts focused in diminishing their morbidity and mortality. Listeria monocytogenes is one of the agents associated in this kind of diseases. In the lactic industry, this bacteria is important since raw milks as well as dairy products have been associated in outbreaks, being fresh cheese one of the most vulnerable products to the contamination with this bacteria. The traditional identification of the bacteria is done by a laborious, time consuming and low sensitive technique and the polymerase chain reaction may allow more precise and exact results in shorter time. For this reason the objective of the present study was to optimize the procedure to determine the sensitivity and specificity limits for the detection of L. monocytogenes from fresh cheese and the predictive value of the test. In order to achieve this objective, 76 pasteurized cheese samples were evaluated (45 samples were artificially inoculated at the lab and 31 were used as negative controls). The validation of the technique was done in 50 samples of non pasteurized fresh cheese. Traditional culture isolation was performed according to the methodology described in Compendium of Methods for the Microbiological Examination of Foods. PCR reaction for the detection of L. monocytogenes was based on the methodology described by Poutou,using primers characteristic of the genus and the listeriolisine O gene that is specie’s specific. The optimal incubation period determined for the selective enrichment broth was of 48h, and a 100% sensitivity, specificity, predictive value (positive and negative ) were obtained by PCR. The technique validation showed the specificity of the test in the detection of only the L. monocytogenes species, and not other genus or species that may appear in food matrixes or in food environments.

Keywords : Listeria monocytogenes; PCR; validation; sensitivity; specificity.