Common Probiotic Microorganisms
There are a number of different microorganisms that are currently used in probiotic supplements. The main species used are highlighted in the table below.
Table 1: Organisms that are currently used in probiotic products (listed by genus and species).[1-5] *= strains of so-called Saccharomyces boulardii have been definitively classified as being in the species Saccharomyces cerevisiae
Why the domination by lactobacilli and bifidobacteria?
The commercial probiotic market is dominated by preparations containing lactobacilli and bifidobacteria. There are probably a number of reasons for this. The popularity of lactobacilli can be traced back to work conducted by Nobel Prize winning scientist Elie Metchnikoff who, in the early 1900s, asserted that the fermented beverage consumed by Bulgarians (which we now call yoghurt) was the elixir of life. The bacteria he isolated from yoghurt came from two species Lactobacillus delbrueckii subspecies bulgaricus and Streptococcus thermophilus. He theorized that the consumption of these bacteria arrested the putrefaction of protein in the bowel. Further, he believed that many diseases, and even ageing itself, were caused by the putrefaction of protein in the bowel by intestinal microbes. He assumed that these two species of bacteria were capable of inhibiting the growth of putrefactive bacteria in the intestines. Thus, yoghurt consumption was recommended to correct this ‘autointoxication’ and improve the composition of the microbiota . The presence of lactobacilli in the human GIT and vagina ecosystems was probably also important in furthering the idea that lactobacilli were of considerable importance to human health. Strains of Streptococcus thermophilus were later discovered to have limited capacity to survive transit through the upper GIT (e.g., stomach and small intestine) and, consequently, have less chance of producing therapeutic effects.
Bifidobacteria were first isolated from the stool of a healthy breast-fed infant by Tissier of the Pasteur Institute in France in 1899. Up until the 1960s, bifidobacteria were considered species of lactobacilli – Lactobacillus bifidus. Their dominance in the microbiota of breast-fed infants and considerable presence in the adult GIT, as well as their lack of pathogenic potential, are the probable reasons for the initial popularity of research examining the therapeutic qualities of bifidobacteria and their inclusion into probiotic preparations.
There is now considerable interest in expanding beyond the traditional probiotic genera (lactobacilli and bifidobacteria) to other novel species of bacteria. In the coming years, there will be an ever-expanding amount of research conducted on the potential health benefits of strains from other bacterial genera, such as Ruminococcus, Roseburia, Faecalibacterium, and Oxalobacter . This will eventually result in the development, and commercialization, of a new wave of probiotic preparations.
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