Suitability of the fluorescent techniques for the enumeration of probiotic bacteria in commercial non-dairy drinks and in pharmaceutical products

The suitability of the fluorescent techniques for the microbiological quality assessment of probiotic non-dairy drinks and probiotic pharmaceutical products was studied. The method optimization was first performed with pure cultures of probiotic strains detected in commercial products (representing Lactobacillus and Bifidobacterium species). Altogether seven different fluorescent viability stains combined with epifluorescence microscopy and flow cytometry were tested. The most applicable stains ChemChrome and LIVE/DEAD BacLight Viability Kit were further used for the viability studies of the commercial probiotic products. The studied products proved to be of good quality. All products contained the probiotic bacterium indicated on the label and the levels of living bacteria were reasonable per dose (108–1010 cells for suggested daily dose of pharmaceutical products and 108–109 cells per 100 ml of drink). The results obtained with fluorescent stains were mostly in agreement with results obtained with culture, rendering fluorescent techniques applicable alternatives for rapid viability assessment of probiotic products. Especially the newly developed fluorometry assay with BacLight proved to be fast and accurate.