Probiotics are defined as live microorganisms, which when administered in adequate amounts, confer a health benefit on the host. Species of Lactobacillus and Bifidobacterium are most commonly used as probiotics. The yeast Saccharomyces boulardii and specific strains of Streptococcus, Pediococcus, Leuconostoc, Bacillus, Escherichia coli are also used as probiotics.
The biological effects of probiotics are strain-specific and that the success or failure of one strain cannot be extrapolated to another strain. Probiotic strains are sub-cultures of almost identical cells, ideally derived from the same mother cell. A probiotic strain is identified by the genus, species, subspecies (if applicable), and an alphanumeric designation that identifies a specific strain. For example, Lactobacillus casei DN-114001 or Lactobacillus rhamnosus GG.
Nomenclature used for probiotic microorganisms
|Genus||Species||Subspecies||Strain Designation||Strain Nickname|
|Bifidobacterium||rnimalis||lactis||DNA-173 010||Bifidus regularis|
Important properties of strains to be considered for probiotics use are:
- ability to reduce pathogen adhesion to surfaces
- adherence to mucus and/or human epithelial cells and cell lines
- antimicrobial activity against potentially pathogenic bacteria or fungi
- bile acid resistance
- Safety in food and clinical use
- resistance to gastric acidity
The genus Lactobacillus includes various Gram-positive facultative anaerobic or microaerophilic rod-shaped bacteria. They are a major part of the lactic acid bacteria (LAB) group that can convert hexose sugars to lactic acid. In humans, Lactobacilli are normally present in the vagina and gastrointestinal tract where they inhibit harmful bacteria by making acidic environments. Some Lactobacilli are used for the production of yogurt, cheese, sauerkraut, pickles, sourdough, wine, and other fermented products.
Lactobacilli species are commonly selected as probiotics since they express many crucial properties such as high tolerance to acid and bile, capability to adhere to intestinal surfaces, withstanding low pH of gastric juice, inhibiting potentially pathogenic species, resisting antibiotics, producing exopolysaccharides, and removing cholesterol. Studies have shown that certain strains of Lactobacilli are effective in preventing antibiotic-associated diarrhea, preventing recurrent UTI in adult women, etc.
Most common probiotic species of Lactobacillus are as follows:
- L. acidophilus
- L. brevis
- L. bulgaricus
- L. casei
- L. paracasei
- L. plantarum
- L. reuteri
- L. rhamnosus
- L. salivarius
- L. plantarum
- L. delbrueckii subsp. bulgaricus
- Lactobacillus animalis subsp. lactis
- Lactobacillus casei strain shirota
Strains of the genus Bifidobacterium are also commonly used as probiotics either alone or in a cocktail with other probiotic bacteria. The genus Bifidobacterium includes various Gram-positive non-motile anaerobic bacteria. They are endosymbiotic inhabitants of the gastrointestinal tract and vagina of mammals, including humans.
Bifidobacterium species have been proven effective to treat constipation, travelers’ diarrhea, antibiotic-associated diarrhea, food allergies, and cholesterol-lowering capacities.
Most common probiotic species of Bifidobacterium are as follows:
- B. adolescentis
- B. bifidum
- B. breve
- B. infantis
- B. longum
- B. lactis
- B.animalis subsp lactis
S. boulardii has been used extensively as a probiotic, both as a dietary supplement and as a drug. S. boulardii is a live yeast and is available in a lyophilized form to treat diarrhea. Administration of S. boulardii has shown positive effects for patients with irritable bowel syndrome, recurrent pseudomembranous colitis, preventing and treating relapses of inflammatory bowel disease, and treating moderate symptoms of ulcerative colitis.
Saccharomyces boulardii fungemia secondary to use of the probiotic has been described for critically ill patients.
S. thermophilus, also known as Streptococcus salivarius subsp. thermophilus is a gram-positive cocci of the group viridans streptococci. Streptococcus thermophilus is used as a starter culture for the production of yogurt alongside Lactobacillus delbrueckii subsp. bulgaricus).
Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus improve lactose digestion and reduce symptoms related to lactose intolerance.
E. faecalis and E. faecium are commonly used probiotic strains of the genera Enterococcus. Enterococcus faecium has been used to prevent antibiotic-associated diarrhea but growing evidence suggests that certain strains of E. faecium can act as an opportunistic pathogen, so they are no longer regarded safe for human consumption. They are still used as probiotics for animals.
Escherichia coli, a prominent member of the family Enterobacteriaceae is an opportunistic pathogen and number one cause of UTI in females. E. coli is a normal flora of the intestine and contains a probiotic strain named E. coli Nissle 1917.
E. coli-based probiotics (E. coli Nissle) have been effective in reducing symptoms of constipation and inflammatory bowel disease (IBD). This strain has the potential to reduce gastrointestinal disorders, ulcerative colitis, Crohn’s disease, even colon cancer, however, more research is necessary.
Bacillus coagulans and Bacillus mesentericus are the most commonly used probiotic species of Bacillus genera and have been used successfully to treat antibiotic-associated diarrhea. Bacillus is a gram-positive spore-forming aerobic or facultative aerobic rod.
References and further readings
- Probiotics and prebiotics. World Gastroenterology Organisation Global Guidelines-2017
- Fijan, S. (2014). Microorganisms with Claimed Probiotic Properties: An Overview of Recent Literature. International Journal of Environmental Research and Public Health, 11(5), 4745–4767. https://doi.org/10.3390/ijerph110504745
- Kneifel, W., & Domig, K. J. (2014). Probiotic Bacteria: Detection and Estimation in Fermented and Nonfermented Dairy Products. In C. A. Batt & M. L. Tortorello (Eds.), Encyclopedia of Food Microbiology (Second Edition) (pp. 154–157). Academic Press. https://doi.org/10.1016/B978-0-12-384730-0.00271-8
- Office of Dietary Supplements—Probiotics. Retrieved June 28, 2021, from https://ods.od.nih.gov/factsheets/Probiotics-HealthProfessional/