Microbiological and genetic analysis of probiotic products licensed for medicinal purposes

The purpose of our study was to investigate both qualitatively and quantitatively the microbial content of probiotic products licensed for medicinal purposes.

Microbiological analysis was performed on five different brands of probiotic products that claimed to contain lactobacilli and/or bifidobacteria. The species were determined based on phenotypic characters, using API 50CH, API 20A, and API rapid ID 32A kits. Bacterial strains belonging to the Bifidobacterium genus were further identified using genotypic methods (amplification of specific DNA fragments by PCR and analysis of their nucleotide sequences). The products were also analyzed for pathogenic bacteria. The number of microorganisms contained in four of the products was determined using the plate-count method and the most-probable-number method. The actual and claimed content of probiotic products was analyzed statistically.

Microbiological and genetic analysis showed that, in terms of quality, only three of the five products contained the bacterial strains claimed on the label. None of the tested products contained pathogens. Quantitative analysis demonstrated that 57 of 64 samples (89% [95% CI: 81-97]) contained bacterial counts at the cell densities (doses) claimed on the label.

Our study demonstrates unsatisfactory qualitative microbiological specification in the tested products. However, there was good quantitative agreement with the labeling. Our findings indicate that regulations governing the labeling of probiotic products are urgently required.