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Aims: The objective of this study was to generate strain-specific genomic patterns of a bank of 67 commercial and reference probiotic strains, with a focus on probiotic lactobacilli., Methods and Results: Pulsed-field gel electrophoresis (PFGE) was used as the primary method for strain differentiation. This method was compared with carbohydrate fermentation analysis. To supplement visual comparison, PFGE patterns were analysed quantitatively by cluster analysis using unweighted pair group method with arithmetic averages. SmaI, NotI and XbaI were found to effectively generate clear and easy-to-interpret PFGE patterns of a range of probiotic strains. Some probiotic strains from different sources shared highly similar PFGE patterns., Conclusions: Results document the value of genotypic strain identification methods, combined with phenotypic methods, for determining probiotic strain identity and relatedness. No correlation was found between relatedness determined by carbohydrate fermentation profiles alone compared with PFGE analysis alone. Some commercial strains are probably derived from similar sources., Significance and Impact of the Study: This approach is valuable to the probiotic industry to develop commercial strain identification patterns, to provide quality control of strain manufacturing production runs, to track use of protected strains and to determine the relatedness among different research and commercial probiotic strains.

Products containing probiotic bacteria are gaining popularity, increasing the importance of their accurate speciation. Unfortunately, studies have suggested that improper labeling of probiotic species is common in commercial products. Species identification of a bank of commercial probiotic strains was attempted using partial 16S rDNA sequencing, carbohydrate fermentation analysis, and cellular fatty acid methyl ester analysis. Results from partial 16S rDNA sequencing indicated discrepancies between species designations for 26 out of 58 strains tested, including two ATCC Lactobacillus strains. When considering only the commercial strains obtained directly from the manufacturers, 14 of 29 strains carried species designations different from those obtained by partial 16S rDNA sequencing. Strains from six commercial products were species not listed on the label. The discrepancies mainly occurred in Lactobacillus acidophilus and Lactobacillus casei groups. Carbohydrate fermentation analysis was not sensitive enough to identify species within the L. acidophilus group. Fatty acid methyl ester analysis was found to be variable and inaccurate and is not recommended to identify probiotic lactobacilli.

A panel of experts sponsored by the California Dairy Research Foundation was convened on January 31, 1992 to discuss the effect of the consumption of lactic cultures on human health. The panel was composed of 10 scientists with diverse applicable specialties. Topics discussed included lactose digestion, diarrheal diseases, chronic kidney disease, cancer, adherence, immune system stimulation, cholesterol reduction, constipation, and safety. Legitimacy of health claims and research needs for these areas were determined. The panel noted the promising results in the areas of positive effects of ingestion of lactic cultures on lactose digestion, some diarrheal illnesses, small bowel overgrowth associated with chronic kidney disease, and reduction of fecal enzymes that may play a role in colon cancer. However, additional research is necessary to confirm the effects in all of these areas. A coordinated research effort between microbiologists and clinicians is essential for the most effective research to ensure the choice of best available strains, the best conditions of analysis, and the best clinical models.

The interactions between lactic acid bacteria and their phages are commercially significant. Current research has focused on the elucidation of the mechanisms and genetics of phage resistance. Phage resistance genes have been linked to plasmid DNA for Streptococcus lactis and Streptococcus cremoris, and preliminary studies suggest the operation of mechanisms such as the prevention of phage adsorption, restriction/modification, and abortive infection. Some phage resistance plasmids can be conjugally transferred, providing a means of dissemination among phage-sensitive strains for the construction of phage-resistant starter cultures.