For centuries living microorganisms, particularly lactic acid bacteria (producers of lactic acid from sugar), have been used in food preservation. So there has been a long-term awareness of the beneficial effects of microorganisms. However, the first reports of beneficial effects on human health linked to lactobacilli and bifidobacteria appeared in the late 19th to early 20th century.

What is a Probiotic?

In 1965, Lilly and Stillwell proposed the term “probiotics” to refer to ‘substances produced by microorganisms which promote the growth of other microorganisms. The most widely adopted definition of probiotics is ‘live microorganisms which, when administered in adequate amounts, confer health benefits on the host’.  Health Canada suggests one possibility for probiotics to confer a health benefit would be by modulating the microbiota indigenous to humans.  Organisms included in probiotic preparations are lactic acid bacteria (such as Lactobacillus acidophilus, L. casei, L. reuteri, L. rhamnosus, Lactococcus lactis), bifidobacteria (eg, Bifidobacterium animalis subsp. lactis, B. bifidum, B. infantis, B. longum), the yeast Saccharomyces boulardii, Enterococcus faecium and Enterococcus faecalis, Escherichia coli Nissle 1917 and Bacillus coagulans (L. sporogenes).

Where Do Probiotics Come From?

The human gastrointestinal (GI) tract has co-evolved with a very complex, stable microbial population (the gut microbiota) of more than 100 trillion microorganisms comprising several hundred different species that has led to the development and optimization of complex immune mechanisms that control this ecosystem. The gut microbiota plays an important role in nutrition and metabolism (digestion, absorption, fermentation, vitamin synthesis and energy production), regulation of immune function (by stimulation of immunoglobulin and cytokine production), and protection (colonization resistance and production of antimicrobial substances). The genomes of the gut microbiota encode for metabolic activities distinct from those of the human microbiota, thus contributing directly to human physiology.

Many factors, such as diet, food poisoning, infections, antibiotic therapy, stress and aging can impact the balance of the gut microbiota, and GI disturbances can range from mild to life-threatening. There is a growing awareness of the importance of the relationship between the gut microbiota and human health and the potential for the manipulation of this relationship to achieve therapeutic effects.

What are the Benefits of Probiotic Use?

The use of the probiotic strains has been widely investigated for a range of conditions, namely, diarrhea in children, antibiotic-associated diarrhea, Clostridium difficile-associated diarrhea, traveler’s diarrhea, irritable bowel syndrome (IBS), inflammatory bowel diseases (Crohn’s disease, ulcerative colitis, pouchitis), pancreatitis, necrotizing enterocolitis, colon cancer, allergic diseases including atopic dermatitis (eczema), urogenital infections, Helicobacter pylori gastric infection, prevention of common cold, winter infections, absences from work, lactose intolerance and oral health. The well-characterized immunomodulatory properties of probiotic bacteria have been used as a tool to alleviate intestinal inflammation, normalize gut mucosal dysfunction and down-regulate hypersensitivity reactions.6 In addition, recent work is identifying the role of probiotic organisms in energy metabolism.

Safety of Probiotics

Reports of infection due to lactobacilli and bifidobacteria (the most abundant probiotic strains) are extremely rare and have been estimated to represent only between 0.05%-0.4% of cases of infective endocarditis and bacteraemia, and these mostly in immunocompromised patients. There is no evidence that ingested probiotic lactobacilli or bifidobacteria pose any risk of infection greater than that associated with commensal strains.7 There is a general consensus of opinion that probiotics such as Lactobacilli and Bifidobacteria are suitable and well tolerated. To our knowledge, there are no reports of serious adverse events attributable to probiotics in healthy individuals.

Applications of Probiotics

Probiotic usage is being advocated within all areas of the GI tract. Within the intestine, the best results relating to the use of probiotics have been obtained for the prevention and treatment of acute diarrhea, including antibiotic-associated and Clostridium difficile-associated diarrhea.  There is also growing evidence for the capacity of probiotics to modulate immune function and reduce intestinal permeability.

The intestinal microbiota is considered a positive health asset that exerts a conditional effect on intestinal homeostasis with resident bacteria delivering regulatory signals to the epithelium to instruct mucosal immune responses. The composition of the gut microbiota is believed to influence the development of the immune response. Kelly et al. suggest that an imbalance between aggressive and protective bacterial species, or loss of gut bacteria that promote tolerance and Treg cell polarization could lead to excessive Th1 or Th2 responses, thus promoting inflammatory or allergic diseases.


The scope of probiotics seems endless. It seems that more and more applications for the involvement of probiotic supplements are being identified, almost on a daily basis. There are inconsistencies in the results that have been obtained, but much of that relates to the testing of a diversity of products with different compositions and potencies. It is apparent that there are benefits from probiotics across a broad spectrum of conditions, many of which are linked with antibiotic therapy. As our knowledge of the value of the GI microbiota is growing, so is the awareness of the potential for probiotics, and as the mechanistic details of the mode of action of probiotics becomes clearer, further developments will occur.

My thanks to my acquaintance Dr. Christine Doherty and her colleagues — Sue Plummer, PhD, Iveta Garaiova, PhD, and Marija Pevac-Djukic, MD, for sharing this valuable information.

Yours in health,

Dr. Francis Gonzalez, ND

(212) 888-9116