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Molecular quantification of lactic acid bacteria in fermented milk products using real-time quantitative PCR.

Furet JP, Quénée P, Tailliez P

Institut National de la Recherche Agronomique, Unité de Recherches Laitières et Génétique Appliquée, Domaine de Vilvert, 78352 Jouy-en-Josas Cedex, France.

Real-time quantitative PCR assays were developed for the absolute quantification of lactic acid bacteria (LAB) (Streptococcus thermophilus, Lactobacillus delbrueckii, L. casei, L. paracasei, L. rhamnosus, L. acidophilus and L. johnsonii) in fermented milk products. The results of molecular quantification and classic bacterial enumeration did not differ significantly with respect to S. thermophilus and the species of the L. casei group which were detected in the six commercial fermented products tested, thus showing that DNA extraction was efficient and that genomic DNA solutions were free of PCR inhibitors. For L. delbrueckii, the results of bacterial enumeration were generally lower by a factor 10 to 100 than those of PCR quantification, suggesting a loss of viability during storage of the dairy products at 1-8 degrees C for most of the strains in this species. Real-time quantitative assays enabled identification of the species of lactic acid bacterial strains initially present in commercial fermented milk products and their accurate quantification with a detection threshold of 10(3) cells per ml of product.

Published 15 November 2004 in Int J Food Microbiol, 97(2): 197-207.
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