The vaginal microbiota and influence of select probiotic Lactobacilli strains

It is important to recognise that not all strains of Lactobacilli, even those widely acknowledged as probiotics for promoting gastrointestinal health, are equally effective in supporting women’s urogenital tract health. For example, daily oral administration of the widely recognised probiotic strain to support gastrointestinal health, L. rhamnosus GG, for 28 days failed to influence vaginal health despite the administration of 10 billion, whereas oral administration of only 1.6 billion of the combination of L. rhamnosus GR-1 and L. reuteri RC-14 supported a healthy vaginal microbiota.¹ Furthermore, daily oral administration of a commercially available dietary probiotic containing L. rhamnosus GG (40 billion) for six months failed to demonstrate vaginal colonisation by this specific L. rhamnosus strain or reduce the recurrence of Urinary Tract Infections (UTIs).²

The majority of probiotic products marketed for support of women’s vaginal health, generally multi-strain combinations of lactobacilli with or without strains from additional genera such as Bifidobacteria, are not supported by clinical research for this indication. Additionally, the strain designation for each bacterium within the combination is often not disclosed (only genus and species). It is well recognised scientifically that probiotics are strain, dose, and condition specific. Strains of the same bacterial species can be different as exemplified by aforementioned examples comparing L. rhamnosus GR-1 vs. L. rhamnosus GG (unique strains of the same bacterial genus and species) to support women’s urogenital tract health (condition), a functional distinction that was not overcome with administration of markedly greater abundance (dose) of L. rhamnosus.

Strain functionality and associated health claims beyond general support of gastrointestinal health in humans require substantiation of efficacy with clinical trials. Strain designation links unique bacterial strains to the scientific research supporting probiotic characteristics and efficacy for a specific condition in target host organisms (e.g., humans). Guidelines established by an expert working group, convened jointly by the FAO of the United Nations and the WHO, state, ‘Proper identification to the level of strain of all probiotics in the product,” and Dr. Mary Ellen Sanders of the International Scientific Association for Probiotics and Prebiotics, an internationally recognised consultant in the area of probiotic microbiology, has stated, ‘Manufacturers should designate the strains in their products so that consumers know what they’re getting. It’s pretty much a consensus among probiotic scientists that this is the responsible thing to do.'

Domig et al. demonstrated an extensive, multi-step scientific process to identify candidate probiotic strains, representing the predominant Lactobacillus species colonising the vagina of healthy pregnant women (L. crispatus, L. jensenii, L. gasseri, L. rhamnosus), for oral administration to support women’s urogenital tract health.62 From 68 isolates belonging to these species, which were derived from 99 isolates from the genus Lactobacillus out of a total of 127 isolates from healthy pregnant women in their late-first trimester, four final candidate strains were selected for targeted formulation based on a battery of criteria such as ability to grow under both aerobic and anaerobic conditions, acidification capacity, glycogen utilisation, extracellular hydrogen peroxide production, stability under acidic conditions and resistance to bile salts (important for survival during gastrointestinal transit post-oral administration), anti-microbial activity against multiple strains of common vaginal pathogens (i.e., Candida albicans, Candida krusei, Candida glabrata, E. coli, and G. vaginalis), compatibility, safety (e.g., lack of virulence factors, antibiotic susceptibility/lack of antibiotic resistance), and encapsulated stability of the multi-strain formulation (forecasting shelf-life stability for use in commercial dietary supplements).

The strains of this probiotic formulation representing the predominant Lactobacillus species of the vaginal microbiota of healthy pregnant women have been designated L. crispatus LBV 88, L. jensenii LBV 116, L. gasseri LBV 150N, and L. rhamnosus LBV 96. These strains, as part of multi-strain probiotic formulation, were subsequently demonstrated in multiple clinical studies to increase vaginal lactobacilli abundance and acidification in support of urogenital tract health. The application of true probiotics to support women’s vaginal health (i.e., clinically validated dosing of probiotic formulations such as L. crispatus LBV 88 + L. jensenii LBV 116 + L. gasseri LBV 150N + L. rhamnosus LBV 96) in clinical practice has gained increasing recognition as a therapy and for prophylactic prevention. However, in a society that focuses on disease and drug therapy more so than natural preventative measures, significant efforts will be needed to get such probiotics into mainstream practice. 

The failure of most medical education programs to teach future physicians about the human microbiota, its relationship to health, and appropriate applications of specific, validated probiotic strains and multi-strain formulations, ultimately diminishes care for patients. It is critical that healthcare practitioners acknowledge the human microbiota and consider its role in health maintenance. Clinical research, dissemination of research results, and education will be key, as confusion about what constitutes a true probiotic-based intervention and misinforming marketing campaigns are widespread.

REFERENCES 1. Kontiokari T, et al. Randomised trial of cranberry-lingonberry juice and Lactobacillus GG drink for the prevention of urinary tract infections in women. BMJ 2001, 322:1571. 2. Domig KJ, et al. Strategies for the evaluation and selection of potential vaginal probiotics from human sources: an exemplary study. Benef Microbes 2014, 5:263-272.