There is a common misconception that probiotics work solely by replacing or “colonizing” the GIT. The reality is that permanent colonization by probiotic bacteria (at least for lactobacilli and bifidobacteria) does not occur and modification of the microbiota is only one of many potential ways that an ingested probiotic strain can influence human health. Once you realize the breadth of potential actions of probiotics, you can start to appreciate their potential value in a broad range of clinical conditions.

Probiotic strains have demonstrated a wide variety of therapeutic effects, which explains why they can be useful for such a diversity of conditions. Such therapeutic actions include:[1]

Immune modulationStrain specificity diagram

Anti-inflammatory activity

Modification of GIT transit

Induction of oral tolerance

Reduced visceral hypersensitivity

Competition for gastrointestinal or vaginal adhesion sites

Antagonism against potential pathogens

Induction of GIT mucin secretion

Enhanced GIT IgA secretion

Directly attaching to rotaviruses

GIT microbiota modification

Breastmilk microbiota modification

Vaginal microbiota modification

Production of beneficial compounds (e.g., short chain fatty acids)

Alteration of the vaginal, intestinal and colonic milieu

Strengthening of the intestinal barrier

Repair of the intestinal barrier

Chemopreventative effects

Metabolism of cholesterol in the GIT

This discussion again points to the importance of choosing the correct strain that has the action you are wanting when treating a specific health condition. For example, a constipated patient with a long gut transit time would need a strain that speeds up transit time. Or a patient with vaginal candidiasis would need a strain with proven anti-Candida actions and a capacity to temporarily colonize the vagina.

Unfortunately, no one strain demonstrates all the therapeutic actions highlighted above – they are not a “one strain fits all” or “one supplement fits all” proposition. Hence, clinicians will need to have a number of different probiotic strains at their disposal to accommodate the breadth of presentations they’ll see in practice.


1. Hawrelak, J., Probiotics, in Herbs & Natural Supplements: An Evidence-based Guide. , L.A. Braun and M. Cohen, Editors. 2015, Elsevier: Sydney. p. 771-795.