Lactobacillus reuteri is a species of lactic acid bacteria. It is considered an autochthonous resident, meaning it is one of the few species naturally indigenous to the gastrointestinal tract of mammals, including humans. It is characterized as a heterofermentative bacterium, capable of producing multiple end products from carbohydrate fermentation, not just lactic acid. This organism was historically isolated from the human gut and human breast milk.
Identifying Natural Food Sources
Finding high concentrations of L. reuteri in standard commercial foods is difficult, setting it apart from many other probiotics. Although historically isolated from human breast milk, its presence in the modern Western diet is not widespread. It is not typically a dominant species in starter cultures used for mass-produced fermented products like commercial yogurts, sauerkraut, or pickles.
Some specialized, traditional fermented foods may contain L. reuteri strains, but the concentration and viability are often inconsistent. Certain types of sourdough bread, specific regional cheeses, and traditionally fermented meats are potential sources. However, achieving a therapeutic dosage, often measured in billions of colony-forming units, through these foods alone is unreliable. Consumers often turn to specialized starter cultures or dietary supplements to ensure a consistent, measurable intake of the specific strain.
Unique Mechanisms of Action
The interest in L. reuteri stems from biological functions that extend beyond simple lactic acid production. A recognized feature is the synthesis of a unique antimicrobial compound called reuterin (3-hydroxypropionaldehyde). This compound is produced when the bacterium metabolizes glycerol, a process requiring the presence of coenzyme B12.
Reuterin acts as a broad-spectrum inhibitor against various pathogenic bacteria, fungi, and protozoa in the gut. This gives L. reuteri a competitive advantage, helping suppress the growth of harmful organisms and maintain a balanced microbial community. The bacteria also adhere directly to the intestinal lining and mucin, utilizing specific surface proteins. This adherence allows the organism to establish a stable presence, reinforcing the mucosal barrier and preventing pathogens from binding to host cells.
Furthermore, specific strains of L. reuteri interact with the host’s immune system by influencing immune cell populations in the gut-associated lymphoid tissue. This immunomodulatory activity includes the potential to increase certain T-lymphocyte populations, such as CD4-positive cells in the ileal epithelium. This may contribute to a balanced inflammatory response.
Culturing and Dietary Strategies for Introduction
Since natural food sources of L. reuteri are limited, the most reliable method for dietary introduction is intentional home culturing. This process involves inoculating a substrate, typically dairy, with a specialized starter culture containing a known L. reuteri strain. The goal of this prolonged fermentation is to achieve a significantly higher bacterial count than is possible with commercial products.
Successful culturing requires precise control over fermentation conditions, particularly temperature and time. The bacteria thrive at a lower temperature range than standard yogurt cultures, typically needing incubation between 97°F and 100°F (36°C to 38°C). The incubation time must be extended, often lasting 24 to 36 hours, allowing the bacteria to proliferate to high numbers.
The process is often enhanced by adding prebiotic fiber, such as inulin, to the substrate. This fiber acts as a nutrient source for the L. reuteri, maximizing its growth. This results in a finished product with hundreds of billions of live bacteria per serving. To maintain viability, the finished cultured product should be refrigerated immediately after fermentation is complete.
Distinguishing L. reuteri from Common Probiotics
L. reuteri is not interchangeable with the general category of probiotics found in many dairy aisles. The beneficial effects of probiotics are highly strain-specific; the actions of one species or strain do not necessarily apply to others. For example, the unique ability to produce the antimicrobial agent reuterin is specific to L. reuteri and is not shared by common yogurt starters like Lactobacillus acidophilus or Streptococcus thermophilus.
The fermentation conditions required for L. reuteri are distinct from those used in commercial food production. Standard yogurt cultures ferment at higher temperatures and for shorter durations, which can be detrimental to L. reuteri viability. Therefore, seeking this bacterium requires looking for products or supplements that specifically list the species, often including the strain designation like ATCC 55730 or ATCC 6475, rather than relying on a general “probiotic” label.