Lactobacillus reuteri is a naturally occurring probiotic bacterium found in the human gastrointestinal tract. Though a member of the Lactobacillus genus, it has recently been reclassified as Limosilactobacillus reuteri. This lactic acid-producing microorganism co-evolved with humans and is considered a normal part of the gut microbiome, even being found in breast milk. The primary interest in this bacterium stems from its documented ability to confer specific health benefits when administered in adequate amounts.
Primary Health Applications
Lactobacillus reuteri has demonstrated specific clinical applications, particularly in managing gastrointestinal and infant health issues. A significant benefit is its effect on infant health, specifically reducing crying time associated with colic. Clinical studies focusing on the strain L. reuteri DSM 17938 show it can significantly decrease the duration of crying in colicky, breastfed infants within a few weeks. This effect is linked to its ability to modulate pain perception and improve gut motility.
In adults, the bacterium supports various gastrointestinal disturbances, including reducing antibiotic-associated diarrhea. For instance, the strain L. reuteri ATCC 55730 reduces the frequency of diarrhea in hospitalized adults at risk for Clostridium difficile infection. It restores a healthier balance to the gut environment following the disruption caused by antibiotic use. Specific strains have also been investigated for their ability to improve gut motility in individuals experiencing functional constipation.
The bacterium also influences immune system modulation beyond the gut lumen. L. reuteri interacts with immune cells in the gut-associated lymphoid tissue, promoting an anti-inflammatory response. Some strains reduce the production of pro-inflammatory cytokines and promote regulatory T cells, which help balance the immune response. This modulation supports the gut barrier function, preventing the translocation of harmful substances into the bloodstream.
L. reuteri also has applications in oral health, helping manage plaque and gingivitis. Certain strains, such as L. reuteri ATCC PTA 5289, are used in products targeting the oral cavity. These strains reduce the levels of pathogenic bacteria, such as Streptococcus mutans, a primary contributor to dental caries. By suppressing these harmful microorganisms, L. reuteri contributes to a more balanced oral microbiome.
Unique Mechanism of Action
The beneficial effects of L. reuteri are driven by its distinct biochemical activity. The most notable mechanism is the production of reuterin, a powerful, broad-spectrum antimicrobial substance. Reuterin is synthesized from glycerol under anaerobic conditions and inhibits the growth of a wide range of harmful organisms, including bacteria, yeasts, and fungi. This allows L. reuteri to shape the microbial community by suppressing potential pathogens, while the bacterium itself remains resistant to reuterin.
L. reuteri also strengthens the intestinal barrier. It stimulates the production of mucus, which forms a protective layer over the epithelial cells lining the digestive tract. Additionally, the bacterium helps increase the expression of tight junction proteins, which seal the spaces between intestinal cells. Reinforcing this physical barrier prevents pathogens and toxins from penetrating the gut wall, reducing inflammation and supporting gut integrity.
Sources and Supplementation
Lactobacillus reuteri is found naturally in the gastrointestinal tracts of humans, other mammals, and human breast milk. Although it exists in the human body, its abundance varies significantly among individuals. Fermented foods may contain L. reuteri, but the levels are often low and unreliable for therapeutic purposes.
For consistent and targeted health benefits, commercial supplementation is the primary source. Supplements are available in various formats, including liquid drops, capsules, chewable tablets, and lozenges. The format choice depends on the target population; drops are common for infants and lozenges for oral health applications.
When selecting a supplement, recognize that the benefits are highly strain-specific. The effects documented in scientific literature are tied to specific designations, such as L. reuteri DSM 17938, studied for infantile colic. Consumers should always look for the specific strain designation listed on the product label to ensure they are getting the strain that corresponds to the desired health benefit.
Safety and Usage Considerations
Lactobacillus reuteri is generally considered safe and well-tolerated across all age groups. The safety profile is supported by extensive clinical trials, with high doses showing no significant safety concerns. Potential side effects are typically mild and transient, involving temporary gastrointestinal discomfort such as gas or bloating.
Dosing typically ranges from 100 million to 100 billion colony-forming units (CFUs) per day, depending on the strain and target condition. For infants and children, the dosage is often limited to approximately one billion CFUs daily. Consult a healthcare provider for guidance on the appropriate dose and duration.
Caution is warranted for certain contraindications. Individuals who are severely immunocompromised or have a central venous catheter should exercise extreme caution, as probiotics have been associated with bloodstream infections in rare instances. Many L. reuteri products require specific storage conditions, such as refrigeration, to maintain the viability of the live bacteria.