Lactobacillus reuteri:
Commonly-Occurring Beneficial Bacteria Also Used in Probiotic Supplements

Lactobacillus reuteri (L. reuteri) is a species of Lactobacillus bacteria that naturally inhabits the digestive tract, the female vaginal and urinary tracts, and breast milk. 

It is also commonly found in some cultured vegetables (such as those in the picture above), in the intestinal tracts of animals, in meat and dairy products, and in the natural environment.

Since it is so widespread, it should not be a surprise to know that specific effects of these bacteria are strain-specific and cannot be generalized across the whole species. The research below shows both species-wide and strain-specific information.

L. reuteri was originally thought to be part of the L. fermentum species, but it was classified as its own distinct species. It is named after the German microbiologist, Gerhard Reuter, who isolated the first strain from human samples.

Most people have heard either all good things about this species or all bad things; the truth lies somewhere in between the two.

Is L. reuteri Safe?

Because L. reuteri as a species is commonly found in foods, the environment and within us, it is generally regarded as safe. It is on the European QPS (Qualified Presumption of Safety) list. Remember, though, that specific strains have specific actions.

What Does Research on Lactobacillus reuteri show?

Research shows:

  • As a species, it is best known for its ability against pathogenic microbes. Some of you may have heard about the broad-spectrum antimicrobial substance, reuterin.
  • Not all strains of L. reuteri produce reuterin, but that is okay because reuterin production is not the only way that members of this species can have beneficial effects.
  • As a species, it also produces carbon dioxide, ethanol, acetic acid and lactic acid from glucose and so is considered to be obligately heterofermentative.
  • It is also able to survive in low-to-no oxygen environments and to produce hydrogen peroxide under the right conditions.
  • It is able to convert lactose to lactic acid which may help with lactose intolerance.
  • Many strains have been recovered from feces showing the ability to withstand stomach acid and bile acids in the digestive tract.
  • Some strains, such as A1, which was recovered from canine feces, are able to withstand the freeze-drying process with no loss of vitality.

Which Strains of Lactobacillus reuteri are the Most Well-Known?

The most well-known strains of L. reuteri are:

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