Species-specific quantification of probiotic lactobacilli in yoghurt by quantitative real-time PCR

Lactobacilli strains with probiotic effects have been widely used in dairy products such as yoghurts as well as in food additives and pharmaceuticals. Despite their successful commercial application, the current species identification and quantification methods of the genus Lactobacillus are time-consuming and labour-intensive.

To fulfil the requirements of a robust quality management, we have developed a quantitative real-time PCR assay based on the heat shock protein 60 gene (hsp60) for accurate identification and quantification of five commercially important Lactobacillus species. The developed assay allows an unambiguous species-specific detection of the species Lact. acidophilus, Lact. brevis, Lact. delbrueckii subsp. bulgaricus, Lact. helveticus and Lact. reuteri from bacterial cultures as well as directly from dairy products for instance yoghurt.

With the assay, we were able to specifically detect lactobacilli strains down to 10(5)  CFU ml(-1) directly from yoghurt, which is a sufficient detection limit as commercial products usually contain 10(6) -10(12)  CFU ml(-1) of probiotic strains.

The real-time PCR assay developed here might become a convenient tool enabling an accurate, fast and sensitive detection of probiotic lactobacilli commercially used in food.