Nancy Toedter Williams


Am J Health Syst Pharm. 2010;67(6):449-458. 

In This Article


Although the exact mechanisms of action of probiotics are not known, several have been proposed. As mentioned previously, the most frequently used probiotics include lactic acid bacteria, particularly Lactobacillus and Bifidobacterium species. These bacteria produce lactic acid, acetic acid, and propionic acid, which lower the intestinal pH and suppress the growth of various pathogenic bacteria, thereby reestablishing the balance of the gut flora.[6,7]

Another mechanism of bacterial interference involves the production of various substances, such as hydrogen peroxide, organic acids, bacteriocins, and biosurfactants, that are toxic to pathogenic microorganisms.[7,10,14] One probiotic with this ability is Lactobacillus species strain GG, which has been shown to secrete a low-molecular-weight compound that inhibits a broad spectrum of gram-positive, gram-negative, and anaerobic bacteria.[19] In addition, S. boulardii, a nonpathogenic yeast, may have a role in Clostridium difficile infection by producing a protease that decreases the toxicity of C. difficile toxins A and B.[20]

Probiotics also decrease colonization of pathogenic organisms in the urinary and intestinal tracts by competitively blocking their adhesion to the epithelium.[14] Lactobacilli have been shown to inhibit the attachment of Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa to uroepithelial cells and intestinal epithelial cells.[21,22] This inhibition may occur because lactobacilli cause steric hindrance and upregulate intestinal mucins, which are high-molecular-weight glycoproteins produced by epithelial cells; the result is the formation of a protective barrier. In addition, lactobacilli strengthen the gut mucosal barrier by stabilizing tight junctions between epithelial cells and decreasing intestinal permeability.[7]

Another proposed mechanism of action of probiotics involves immunomodulation. Animal studies have found that some probiotic strains augment the immune response by stimulating the phagocytic activity of lymphocytes and macrophages.[18] Probiotics also increase immunoglobulin A (IgA) and stimulate cytokine production by mononuclear cells.[15,18] Kaila et al.[23] found that children with acute rotaviral diarrhea who were given Lactobacillus rhamnosus strain GG (LGG) had an increased IgA, immunoglobulin G, and immunoglobulin M response, resulting in a shortened duration of gastroenteritis symptoms.

Numerous health effects are associated with probiotic use. While some of these indications are well documented, probiotics are often used to treat conditions for which data regarding the efficacy of probiotics are lacking or conflicting.[3,9,24] This article focuses on the more-common uses of probiotics.


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