Rapid and specific enumeration of viable Bifidobacteria in dairy products based on flow cytometry technology: A proof of concept study

A rapid and specific analytical method to enumerate viable Bifidobacteria in dairy products containing a mix of lactic acid bacteria was developed to proof of concept. A polyclonal antibody against Bifidobacterium animalis ssp. lactis (B. lactis) was used for specific detection by flow cytometry (FCM). The antibody, which targeted the cell wall of B. lactis, had a high labelling efficiency of 95.5 ± 1.9% of the population. A viability probe, 5,6-carboxyfluorescein diacetate, was combined with the antibody for real-time quantification of viable B. lactis. Enumeration results from FCM on four different commercial dairy products that contain B. lactis showed a good correlation with the standard culture-based method. Moreover, it provided a species-specific method to enumerate viable B. lactis within 2 h; the standard method counts the total cultivable Bifidobacteria genus on plates after 72 h. This study demonstrated that FCM could be a rapid solution for probiotic analysis in dairy products.