The Scientific Basis for Probiotic Strains of Lactobacillus

While many Lactobacillus strains have been promoted as good probiotics for human usage, there are relatively few with substantial supporting in vitro and human data. Biotherapeutic properties and mechanisms of action are too often lacking, and arguably too many human studies are undertaken or contemplated with strains which have not been thoroughly characterized with respect to the intended site of insertion. There are a few notable exceptions, including those described in this review, which have been well studied, and the findings have been documented in peer-reviewed journals. With respect to site of action and speciation, it is premature to suggest that certain species will function in only one site, although L. reuteri is rarely found in the vagina and likely will be better suited to intestinal application. The challenge in the future will be to better understand how these seven organisms, and indeed other purported probiotic lactobacilli, interact within the microbial biofilms of the intestine and urogenital tract and how they and indigenous members of the normal flora restore and maintain health. Recent advances in the study of biofilms, such as use of confocal microscopy and the discovery of cell-to-cell signaling, will provide useful road maps for investigating the interactions between exogenous and indigenous lactobacilli and intestinal and urogenital biofilms. With the increased evidence of multidrug resistance among pathogens and a continued failure to manage gastrointestinal virus infections, plus a desire by consumers to use natural methods for health maintenance rather than long-term chemotherapeutic agents, the time is right for probiotics to be taken seriously. It is also time for scientists to provide the data which give a basis and mechanism of action for the human utilization of well-studied organisms.