What Is Reuteri? Benefits, Strains, and Sources

Reuteri, formally known as Limosilactobacillus reuteri (and still widely labeled by its older name Lactobacillus reuteri), is a species of lactic acid bacterium that naturally colonizes the gastrointestinal tracts of humans and other vertebrates. It has become one of the most studied probiotic organisms in the world, with clinical research spanning infant colic, cholesterol management, bone density, and gut pathogen suppression. What makes it unusual among probiotics is the degree to which its strains have diverged to match specific hosts and health targets, meaning that “reuteri” is less a single supplement ingredient and more a family of related organisms with distinct capabilities.

A Bacterium That Evolved Alongside Its Host

L. reuteri has a remarkably intimate relationship with vertebrate animals. Genetic studies show it has diversified into host-specific lineages over long evolutionary timescales, with strains isolated from rodents, poultry, pigs, and humans forming distinct genetic clusters that reflect the animal they came from rather than the geographic region where they were collected.¹ When researchers tested this in germ-free mice, rodent-derived strains outcompeted strains from other hosts, confirming that the relationship is not random but adaptive.² Genomic comparisons show that human strains are markedly different in gene content from rodent or poultry strains, reflecting the particular niches each lineage has adapted to.³

This matters practically because a rodent study on a mouse-derived strain of L. reuteri does not automatically predict what a human-derived strain will do in your body. The strain’s evolutionary background shapes which genes it carries for surface proteins, carbohydrate metabolism, and antimicrobial production.⁴ This is one reason the probiotic field has shifted toward naming specific strains on product labels rather than just the species.

How It Works Once It Reaches Your Gut

L. reuteri has a signature trick: it converts glycerol (a simple molecule found in dietary fats) into a compound called reuterin, which acts as a broad-spectrum antimicrobial. Reuterin inhibits both gram-positive and gram-negative bacteria, giving L. reuteri a chemical weapon against gut pathogens.⁵ Reuterin is chemically a mixture of forms of 3-hydroxypropionaldehyde and is potent enough to be explored as a food preservative in its own right.⁶

But reuterin production is not the only thing L. reuteri does. Depending on the strain, it can also produce bile salt hydrolase (an enzyme that breaks down bile salts and influences cholesterol metabolism), modulate the immune system by promoting regulatory T cells, and interact with the vagus nerve in ways that affect brain signaling. These mechanisms are strain-dependent, which is why the research literature is careful to specify which strain produced which result.

One of the more practical implications of reuterin production is the role glycerol plays as a fuel. Research on oral biofilms found that supplementing L. reuteri with glycerol significantly boosted its antimicrobial activity against periodontal pathogens, turning a modest probiotic effect into a stronger one.⁷ This synbiotic approach (pairing the bacterium with its preferred substrate) is an emerging strategy in probiotic design.

Surviving Stomach Acid and Bile

A probiotic is useless if it dies before reaching the intestine. L. reuteri is unusually tough in this regard. In laboratory conditions, more than 80% of cells survived at pH 2.7 for an hour, a level of acidity comparable to the human stomach.⁸ The bacterium activates a suite of stress-response genes that help it maintain membrane integrity and cell wall structure under acidic conditions. Separate research identified genes that help L. reuteri survive bile salts in the small intestine, including a multidrug resistance transporter that allows the bacterium to restart growth after bile exposure.⁹

Interestingly, exposure to one type of stress can cross-protect L. reuteri against others. A strain pre-adapted to acid stress showed improved survival when subsequently exposed to bile salts and even freeze-drying, thanks to the upregulation of overlapping protective genes.¹⁰ This cross-protection is relevant to supplement manufacturing, where freeze-drying is the standard method for preserving probiotic cells.

The Major Strains and What Each One Does

If you look at L. reuteri research and supplement labels, a handful of strain designations appear repeatedly. Each has its own body of evidence, and they are not interchangeable.

DSM 17938: The most studied strain for infant colic and pediatric gut health. It was derived from an older commercial strain (ATCC 55730) after researchers removed plasmids carrying antibiotic resistance genes, creating a cleaner version with the same probiotic properties.
ATCC PTA 6475: The bone health strain, studied in older women with low bone mineral density and also investigated for oxytocin-related effects on social behavior in animal models.
NCIMB 30242: The cardiovascular strain, tested for its bile salt hydrolase activity and its ability to lower LDL cholesterol.
DSM 17648: An inactivated (heat-killed) form studied for its ability to bind to and help clear Helicobacter pylori from the stomach.
ATCC PTA 5289: Studied for oral health applications, particularly its antimicrobial activity in dental biofilms.

The distinction between these strains is not cosmetic. DSM 17938 and ATCC PTA 6475 belong to different evolutionary lineages of L. reuteri and carry different functional genes. A supplement that lists only “L. reuteri” without a strain number is not giving you enough information to know which effects to expect.

Infant Colic and Crying Time

The strongest human evidence for L. reuteri is in breastfed infants with colic. A meta-analysis pooling data from multiple randomized trials found that infants receiving L. reuteri (strain DSM 17938) cried roughly 25 fewer minutes per day than the placebo group by day 21 and were almost twice as likely to experience a meaningful reduction in symptoms. The effect was dramatic in breastfed infants, with a very favorable number needed to treat, but was not significant in formula-fed infants.¹¹

Individual trials back this up. One double-blind, placebo-controlled trial showed that by day 21, the median crying time in the L. reuteri group had dropped to 35 minutes per day compared to 90 minutes in the placebo group.¹² A real-world clinic-based study found that 85% of infants experienced at least a 50% reduction in crying time by the end of the study period.¹³ The breastfed-versus-formula-fed distinction is an important caveat that often gets lost in consumer marketing: if your infant is formula-fed, the evidence supporting L. reuteri for colic is much weaker.

Suppressing H. Pylori in the Stomach

Helicobacter pylori infects roughly half the world’s population and is a leading cause of gastritis and stomach ulcers. L. reuteri has been studied both as a standalone treatment and as a helper alongside standard antibiotic therapy. A pilot study found that four weeks of L. reuteri supplementation (strain ATCC 55730) reduced H. pylori levels in the stomach and improved gastrointestinal symptoms compared to placebo.¹⁴

More recently, an inactivated form of L. reuteri (strain DSM 17648), used as a postbiotic alongside standard triple therapy, achieved an eradication rate of about 97% compared to 86% with standard therapy plus placebo.¹⁵ The fact that even heat-killed cells worked here suggests the mechanism involves physical binding to H. pylori rather than live antimicrobial production. One smaller study that tried L. reuteri alone (without antibiotics) against standard triple therapy found comparable eradication rates between the two, though neither group had a particularly high clearance rate and the study was underpowered to draw firm conclusions.¹⁶ The most promising current approach seems to be using L. reuteri as an adjunct to standard therapy, not a replacement for it.

Cholesterol and Cardiovascular Markers

The strain NCIMB 30242 produces an enzyme called bile salt hydrolase that breaks down bile salts in the small intestine. Because the body uses cholesterol to make new bile salts, this process can lower circulating cholesterol. In a trial of adults with elevated cholesterol, consuming a yogurt containing microencapsulated NCIMB 30242 twice daily for six weeks led to roughly a 9% drop in LDL cholesterol compared to placebo, along with about a 5% reduction in total cholesterol.¹⁷ These are modest but meaningful effects, comparable in magnitude to dietary interventions like increasing soluble fiber intake. Worth noting: this is one trial, and the strain is specific. Other L. reuteri strains that lack bile salt hydrolase activity would not be expected to have the same effect.

Bone Density in Older Women

One of the more surprising lines of L. reuteri research involves bone health. A randomized, double-blind trial in older women with low bone mineral density found that one year of daily supplementation with L. reuteri ATCC PTA 6475 reduced the loss of total volumetric bone mineral density by about half compared to placebo. The treatment group lost roughly 0.83% of bone density compared to 1.85% in the placebo group.¹⁸ Follow-up analysis of the same trial participants found that L. reuteri supplementation also counteracted degradation of the gut microbiota composition that normally occurs with aging.¹⁹

Animal studies have extended this finding, showing that even heat-killed L. reuteri ATCC PTA 6475 prevented bone loss in mice that had their ovaries removed (a standard model for postmenopausal osteoporosis).²⁰ This is still early evidence, and the human trial was a single study in a specific population, but it is one of the few probiotic interventions to show a measurable bone-protective effect in humans.

Immune Effects and the Gut-Brain Axis

In mouse models, oral L. reuteri supplementation increased the number of regulatory T cells in the spleen. When those regulatory T cells were transferred to allergen-sensitized mice, they dampened the allergic airway response, reducing inflammation and airway hypersensitivity.²¹ This finding remains confined to animal models, and no large human trial has confirmed that L. reuteri can meaningfully prevent or treat allergies. But it illustrates the broad immunomodulatory reach of this organism.

Perhaps the most intriguing animal research involves the gut-brain connection. Multiple research groups have found that L. reuteri can reverse social deficits in mouse models of neurodevelopmental disorders. The mechanism appears to involve the vagus nerve and upregulation of the hormone oxytocin.²² Separate work has confirmed that L. reuteri upregulates endogenous oxytocin in animal models, with downstream effects on wound healing, immune function, and reproductive fitness.²³ These are fascinating results, but the leap from mouse social behavior to human neurological outcomes is enormous, and no controlled human trial has yet tested whether L. reuteri improves social cognition or mood.

Where You Find It Naturally

L. reuteri is one of the organisms naturally present in sourdough bread starters, where it often dominates the lactic acid bacteria population.²⁴ It also appears in other traditionally fermented foods, breast milk, and the gastrointestinal tracts of healthy humans, though its abundance in the modern Western gut has declined compared to populations eating more traditional diets. You will not get clinically meaningful doses from eating sourdough bread, since baking kills the bacteria, but the presence of L. reuteri in these niches is part of why it has been such a focus of probiotic research: it has a long history of coexistence with humans.

Most people who want a therapeutic dose rely on supplements. These typically contain one of the well-characterized strains listed above, freeze-dried and delivered in capsules, tablets, or chewable lozenges (particularly for oral health applications). Infant formulas have also been developed with L. reuteri and prebiotic fibers like galacto-oligosaccharides and fructo-oligosaccharides, which support the growth of beneficial gut bacteria alongside the probiotic.²⁵

Supplement Viability and What to Look For

One of the ongoing challenges with L. reuteri supplements is keeping the bacteria alive through manufacturing, storage, and your digestive tract. Encapsulation technologies, including spray drying, ionic gelation, and electrospray methods combined with protective biopolymers, are used to shield the bacteria from heat, moisture, and acid.²⁶ Laboratory tests show that encapsulating L. reuteri in emulsions with higher concentrations of wall materials (like whey protein concentrate and gum arabic) improved both encapsulation efficiency and survival during simulated digestion.²⁷

For consumers, the practical takeaway is to look for products that specify the strain designation, list a colony-forming unit (CFU) count guaranteed through the expiration date (not just at the time of manufacture), and store the product as recommended. Refrigerated products generally retain higher viable counts than shelf-stable ones, though some encapsulated formulations are designed to be stable at room temperature.

Safety and the Antibiotic Resistance Question

L. reuteri has a strong safety record. A phase-one safety study in a population in the Peruvian Amazon found no evidence of invasive infection from probiotic administration and no differences in adverse events between the probiotic and control groups.²⁸ This aligns with the general safety profile of Lactobacillus-family probiotics in immunocompetent people.

One concern that has received careful attention is antibiotic resistance. Research found that a majority of L. reuteri strains carried resistance genes for tetracycline, and some carried resistance genes for erythromycin, often on plasmids that could theoretically be transferred to other bacteria.²⁹ This is precisely why the widely used strain DSM 17938 was created. Researchers took the original commercial strain ATCC 55730, identified two plasmids carrying tetracycline and lincosamide resistance genes, and removed them without genetic modification. The resulting daughter strain, DSM 17938, lost those resistances while retaining its probiotic properties, as confirmed both in laboratory tests and a human clinical trial.³⁰ This story is actually a good example of the probiotic field policing itself: when a potential safety issue was identified, the strain was cleaned up rather than ignored.

Wound Healing and Skin Applications

A newer and more experimental area of L. reuteri research involves wound healing. In cell culture and mouse studies, L. reuteri extracts accelerated wound closure by promoting the proliferation and activation of fibroblasts, the cells responsible for rebuilding tissue.³¹ A separate study found that one specific strain, L. reuteri NCHBL-005, significantly outperformed other lactobacilli at wound closure in cell models, and topical application in mice enhanced healing confirmed by tissue analysis. The effect depended on the bacterium activating a specific receptor on fibroblasts, and when that receptor was knocked out, the wound healing benefit disappeared.³²

Researchers have even embedded L. reuteri into dissolving microneedle patches for infected wounds. In a mouse model of skin wounds infected with Staphylococcus aureus, a single application of the microneedle patch outperformed control treatments in both clearing infection and promoting healing.³³ These are all preclinical findings with no human wound trials yet, but they point to a future where L. reuteri-based products might be applied to the skin rather than swallowed.

The Name Change You Will See on Labels

If you have been reading about L. reuteri for a while, you may have noticed that some recent papers and products call it Limosilactobacillus reuteri instead of Lactobacillus reuteri. In 2020, taxonomists reclassified the enormous genus Lactobacillus into 25 smaller genera based on genomic analysis, and the L. reuteri group was moved into the newly created genus Limosilactobacillus.³⁴ The organism itself has not changed. Supplements, clinical papers, and food labels are gradually adopting the new name, but many still use the old one, and both refer to the same species. If you see either name followed by the same strain number, it is the same product.

Oral Health and Its Limits

L. reuteri strains, particularly ATCC PTA 5289, have been explored for oral health on the basis that their antimicrobial activity could suppress the bacteria responsible for gum disease and cavities. The combination of L. reuteri’s reuterin production and its antioxidant-adjacent effects has shown potential in treating oral diseases in laboratory and small clinical settings.³⁵ However, results in clinical trials have been more mixed than the marketing suggests. A randomized trial in patients with both periodontitis and diabetes found that adding an L. reuteri probiotic alongside standard gum treatment provided no additional clinical or microbiological benefit compared to standard treatment plus placebo.³⁶ This is a good reminder that laboratory antimicrobial activity does not always translate to meaningful clinical improvement, especially in complex conditions like diabetic periodontal disease. Oral probiotic lozenges containing L. reuteri remain popular, and there is enough suggestive evidence to justify continued research, but anyone expecting a probiotic lozenge to replace professional dental care will be disappointed.