Detection and enumeration of Lactobacillus helveticus in dairy products

Lactobacillus helveticus, a lactic acid bacterium, is an important species in food fermentation, e.g., cheesemaking, and is considered beneficial to human health. We developed a quantitative real-time polymerase chain reaction (qPCR) method for the detection and quantification of L. helveticus in dairy products. The method uses a set of target-specific PCR primers and a fluorogenic probe and amplifies a part of the pheS gene that encodes the alpha subunit of the phenyalanine-tRNA synthetase. All 24 L. helveticus strains tested were qPCR positive; no signal was observed for 23 strains belonging to closely related species. The limit of detection was ten copies per reaction and the assay covered a linear dynamic range of eight logs. The method was used to detect and enumerate L. helveticus in milk and cheese during ripening; therefore it can be used to study the temporal and spatial distribution of L. helveticus during cheese manufacturing and ripening.