Limosilactobacillus reuteri

What it is

Limosilactobacillus reuteri is a lactic acid bacterium that lives in the gut of many mammals and birds. It was called Lactobacillus reuteri until the 2020 reclassification. Strain DSM 17938 is a 'daughter' of the older commercial strain ATCC 55730. It was made by removing two plasmids that carried tetracycline and lincosamide resistance genes.

What the research says

Results for infant colic conflict. A large Australian community trial (167 infants) found that DSM 17938 did not help, and probiotic babies cried or fussed 49 minutes more. A pooled analysis of the raw data from four trials found it worked in breastfed babies but not clearly in formula-fed babies. A Cochrane review of probiotics given to prevent colic found no clear reduction in colic cases, with low-certainty evidence. As an add-on to H. pylori antibiotics, meta-analyses consistently report fewer side effects, but disagree on whether it improves eradication. Rare invasive infections linked to probiotics have been reported in children, almost all of whom had a predisposing condition such as prematurity or an intravenous catheter.

Evidence grade: Disputed.

What goes wrong

A systematic review of 49 case reports of probiotic-linked invasive infection in children found Lactobacillus species in 35% of cases; across all cases, not only the Lactobacillus ones, all but one child had a predisposing condition, the most frequent being prematurity (55%) and intravenous catheter use (51%). (Source 1)

• Systematic review, Very low certainty.
• Size: 49 case reports.
• Who: Children, 80% under 2 years.
• How long: Reports 1995 to June 2021.
• Result: Lactobacillus spp. 35% of cases; across all 49 cases: under 2 years 80%, sepsis 69.4%, prematurity 55%, intravenous catheter 51% (separate, overlapping proportions), 3 deaths (6%). The passage does not attribute cases to DSM 17938 specifically.
• Funding: not stated in the passage we fetched.

The infections were caused by Lactobacillus spp. (35%), Saccharomyces spp. (29%), Bifidobacterium spp. (31%), Bacillus clausii (4%), and Escherichia coli (2%). Most (80%) patients were younger than 2 years old and sepsis was the most observed condition (69.4%). All the patients except one had at least one condition facilitating the development of invasive infection, with prematurity (55%) and intravenous catheter use (51%) being the most frequent.

The US FDA warned in 2023 that giving probiotics to preterm infants may cause invasive and potentially fatal infection (reported by the NIH Office of Dietary Supplements). (Source 2)

• Official position, Certainty not rated.
• Size: not applicable.
• Who: Preterm infants.
• How long: not applicable.
• Result: No numbers in the passage.
• Funding: government (FDA / NIH)

administering probiotics to preterm infants may cause infection or invasive and potentially fatal disease

The parent strain ATCC 55730 carried potentially transferable antibiotic resistance genes; DSM 17938 was derived by removing those plasmids. (Source 3)

• Lab study in cells, Certainty not rated.
• Size: not applicable.
• Who: Laboratory strains.
• How long: not applicable.
• Result: tet(W) and lnu(A) resistance plasmids removed in DSM 17938.
• Funding: not stated in the abstract.

Lactobacillus reuteri ATCC 55730 is a commercially available probiotic strain which has been found to harbor potentially transferable resistance genes.

What the evidence supports

An individual participant data meta-analysis of four trials found that infants given DSM 17938 were almost twice as likely as those on placebo to have treatment success, with large effects in breastfed infants and insignificant effects in formula-fed infants. (Source 4)

• Meta-analysis, Certainty not rated.
• Size: 345 infants in 4 double-blind trials.
• Who: Infants with colic.
• How long: 21 days.
• Result: Day-21 treatment success incidence ratio 1.7 (95% CI 1.4 to 2.2); in breastfed infants number needed to treat 2.6 (95% CI 2.0 to 3.6).
• Funding: not stated in the passage we fetched.

The probiotic group was almost twice as likely as the placebo group to experience treatment success at all time points (day 21 adjusted incidence ratio 1.7 [95% CI: 1.4 to 2.2]). Intervention effects were dramatic in breastfed infants (number needed to treat for day 21 success 2.6 [95% CI: 2.0 to 3.6]) but were insignificant in formula-fed infants.

The same meta-analysis found fewer antibiotic-related side effects with L. reuteri. (Source 5)

• Meta-analysis, Low certainty.
• Size: 378 patients in 6 RCTs.
• Who: Patients receiving anti-H. pylori therapy.
• How long: Treatment courses.
• Result: Total side effects RR 0.55 (95% CI 0.39-0.77, P = 0.0006).
• Funding: not stated in the passage we fetched.

The incidence of total antibiotic-related side effects was lower in the Lactobacillus reuteri supplementation group than in the control group, with a pooled RR value of 0.55 (95% CI: 0.39–0.77, P = 0.0006)

An updated meta-analysis (conference abstract) of seven trials reported a higher H. pylori eradication rate when L. reuteri was added to triple therapy. (Source 6)

• Meta-analysis, Certainty not rated.
• Size: 518 patients in 7 RCTs.
• Who: Patients receiving standard triple therapy.
• How long: Treatment courses.
• Result: Eradication HR 1.16 (95% CI 1.03-1.31, p = 0.01).
• Funding: not stated in the passage we fetched.

We found that patients who received L. reuteri added to their triple therapy showed a higher eradication rate than those with triple therapy alone (HR: 1.16, 95% CI [1.03, 1.31], p = 0.01).

What the evidence does not support

A double-blind community trial in Melbourne found that L. reuteri DSM 17938 did not reduce crying in colicky infants; the probiotic group cried or fussed more. (Source 7)

• Randomized trial, Moderate certainty.
• Size: 167 infants randomised, 127 analysed for the primary outcome.
• Who: Breastfed and formula-fed infants under 3 months with colic (Australia)
• How long: 1 month.
• Result: Probiotic group cried or fussed 49 minutes more per day at 1 month (95% CI 8 to 90, P=0.02); no study-related adverse events.
• Funding: not stated in the passage we fetched.

At 1 month, the probiotic group cried or fussed 49 minutes more than the placebo group (95% confidence interval 8 to 90 minutes, P=0.02); this mainly reflected more fussing, especially for formula fed infants.

The same meta-analysis found insufficient data to conclude that DSM 17938 helps formula-fed infants with colic. (Source 8)

• Meta-analysis, Certainty not rated.
• Size: 345 infants in 4 trials.
• Who: Formula-fed infants with colic.
• How long: 21 days.
• Result: Effects insignificant in formula-fed infants.
• Funding: not stated in the passage we fetched.

There were insufficient data to make conclusions for formula-fed infants with colic.

A Cochrane review of probiotics given to healthy newborns to prevent colic found no clear difference in new cases of colic, with low-certainty evidence. (Source 9)

• Systematic review, Low certainty.
• Size: 6 studies, 1886 participants (2 used L. reuteri DSM)
• Who: Healthy newborns under one month.
• How long: Varied.
• Result: New cases of colic: RR 0.46 (95% CI 0.18 to 1.19), 3 studies, 1148 participants; I2 = 72%.
• Funding: not stated in the passage we fetched.

A random-effects meta-analysis of three studies (1148 participants) found no difference between the groups in relation to occurrence of new cases of colic: risk ratio (RR) 0.46, 95% confidence interval (CI) 0.18 to 1.19; low-certainty evidence; I2 = 72%.

A meta-analysis of six trials found that adding L. reuteri to H. pylori treatment did not significantly raise eradication rates. (Source 5)

• Meta-analysis, Low certainty.
• Size: 378 patients in 6 RCTs.
• Who: Patients receiving anti-H. pylori therapy.
• How long: Treatment courses.
• Result: Eradication RR 1.12 (95% CI 0.98-1.27, P = 0.09).
• Funding: not stated in the passage we fetched.

An intention-to-treat analysis via a fixed-effects model showed that the pooled relative risk (RR) for the eradication rate was higher for the Lactobacillus reuteri supplementation group than for the control group, but the difference was not significant

Where the evidence is mixed

The same Cochrane review's authors concluded that daily crying time appeared to reduce with probiotics compared with placebo, although there was no clear evidence that probiotics prevent colic. (Source 10)

• Systematic review, Low certainty.
• Size: 6 studies, 1886 participants.
• Who: Healthy newborns under one month.
• How long: Varied.
• Result: Stated qualitatively in the authors' conclusions. The review rated the certainty of evidence low across all three outcomes (ong-2019-e). Its L. reuteri subgroup result for crying time came from studies with very high heterogeneity, so no single figure is given here.
• Funding: not stated in the passage we fetched.

There is no clear evidence that probiotics are more effective than placebo at preventing infantile colic; however, daily crying time appeared to reduce with probiotic use compared to placebo.

Where the research disagrees

Whether L. reuteri DSM 17938 treats infant colic

• Sung et al. 2014 (Australian community RCT), RCT, 167 infants: "L reuteri DSM 17938 did not benefit a community sample of breastfed infants and formula fed infants with colic." (Source 11)
• Sung et al. 2018 (individual participant data meta-analysis), IPD meta-analysis, 4 trials, 345 infants: "L reuteri DSM17938 is effective and can be recommended for breastfed infants with colic." (Source 12)

Whether L. reuteri improves H. pylori eradication

• Yang et al. 2021, Meta-analysis, 6 RCTs, 378 patients: "Lactobacillus reuteri supplementation during anti-Helicobacter pylori treatment may not be effective for improving H. pylori eradication rates." (Source 13)
• Elkoumi et al. 2025 (conference abstract), Meta-analysis, 7 RCTs, 518 patients: "patients who received L. reuteri added to their triple therapy showed a higher eradication rate than those with triple therapy alone" (Source 6)

How much

• Reference intake: No RDA, AI or other reference intake exists for L. reuteri or any probiotic organism. The NIH Office of Dietary Supplements describes product amounts in CFU. (Source 14)
• Upper limit: No tolerable upper intake level has been set for any probiotic organism. (Source 14)
• Studied: Colic trial (Sung 2014): oral L. reuteri DSM 17938 at 1 x 10^8 colony forming units daily, versus placebo, for one month in infants under 3 months. (Source 7)

A common belief, and what the research shows

The belief: L. reuteri DSM 17938 is proven to cure colic in all babies.

What the research shows: The largest community trial found no benefit: "L reuteri DSM 17938 did not benefit a community sample of breastfed infants and formula fed infants with colic." The pooled analysis that found a benefit limited it to breastfed infants and said "There were insufficient data to make conclusions for formula-fed infants with colic."

Questions and answers

What is it?

Limosilactobacillus reuteri (formerly Lactobacillus reuteri) is a bacterium used as a probiotic. The older commercial strain ATCC 55730 carried two plasmids with tetracycline and lincosamide resistance genes; strain DSM 17938 was made from it by removing those plasmids, and it lost those resistances. Lab tests and a human clinical trial found the daughter strain kept its probiotic properties. (Source 15)

What does it do in the body?

Given alongside H. pylori antibiotic treatment, a meta-analysis found L. reuteri may not improve eradication rates, but it can reduce treatment-related side effects and relieve most disease-related symptoms. The authors advise caution because few trials were included. Colic results are set out in the findings. (Source 13)

Is it good or bad for you?

In a double-blind community trial in infants with colic, no study-related adverse events occurred with DSM 17938, but it did not help: at 1 month the probiotic group cried or fussed 49 minutes more per day than the placebo group. Other evidence, including rare infections linked to probiotics, is set out in the findings. (Source 7)

How do you get more of it?

L. reuteri lives naturally in the digestive tract of many mammals, including humans, pigs, dogs, sheep and cattle, and of birds. The sources we cite do not describe a food, supplement dose or behaviour shown to raise it in people. (Source 16)

If it is harmful, what reduces it?

It is not normally considered harmful, so this usually does not apply. In reported probiotic-linked infections in children, almost all patients had a predisposing condition, such as prematurity or an intravenous catheter. (Source 1)

Why might someone be low in it or missing it?

In more recent studies L. reuteri has been found at low prevalence in humans. Researchers suggest this points to a reduction in the human L. reuteri population over the past 50 years. (Source 17)

Which whole foods contain it or feed it?

We found no study showing a whole food that reliably contains L. reuteri DSM 17938. (Source 18)

We searched: Web searches for L. reuteri and DSM 17938 in fermented and other whole foods; Walter, Britton and Roos 2011 review of L. reuteri ecology, which describes where the species lives but not a food source of the strain.

What happens if you do not have it?

No study we found shows that people without L. reuteri come to harm because of its absence. Many healthy people do not carry it. (Source 18)

We searched: Web searches for L. reuteri absence, loss and health outcomes; Walter, Britton and Roos 2011 review on L. reuteri ecology. It describes low carriage in humans but no disease caused by its absence.

How can you test for it?

When seven direct-to-consumer gut microbiome testing services analysed the same standard sample, the variability between providers was on the same scale as the biological variability between different people's samples. (Source 19)

References

1. Children (MDPI). Invasive Infections Associated with the Use of Probiotics in Children: A Systematic Review. 2021. PMID 34682189, DOI 10.3390/children8100924. Read the source
2. NIH Office of Dietary Supplements. Probiotics: Fact Sheet for Health Professionals. 2025. Read the source
3. Applied and Environmental Microbiology. Removal of Antibiotic Resistance Gene-Carrying Plasmids from Lactobacillus reuteri ATCC 55730 and Characterization of the Resulting Daughter Strain, L. reuteri DSM 17938. 2008. DOI 10.1128/AEM.00991-08. Read the source
4. Pediatrics. Lactobacillus reuteri to Treat Infant Colic: A Meta-analysis. 2018. PMID 29279326, DOI 10.1542/peds.2017-1811. Read the source
5. Medicine in Microecology. Efficacy of Lactobacillus reuteri supplementation therapy for Helicobacter pylori eradication: A meta-analysis of randomised controlled trials. 2021. DOI 10.1016/j.medmic.2021.100036. Read the source
6. Open Forum Infectious Diseases (conference abstract supplement). P-96. Efficacy and Safety of Lactobacillus reuteri Supplementation Combined with Triple Therapy for Eradicating Helicobacter pylori: An Updated Meta-Analysis of Randomized Controlled Trials. 2025. DOI 10.1093/ofid/ofae631.303. Read the source
7. BMJ. Treating infant colic with the probiotic Lactobacillus reuteri: double blind, placebo controlled randomised trial. 2014. PMID 24690625, DOI 10.1136/bmj.g2107. Read the source
8. Pediatrics. Lactobacillus reuteri to Treat Infant Colic: A Meta-analysis. 2018. PMID 29279326, DOI 10.1542/peds.2017-1811. Read the source
9. Cochrane Database of Systematic Reviews. Probiotics to prevent infantile colic (Cochrane review summary and abstract). 2019. PMID 30865287, DOI 10.1002/14651858.CD012473.pub2. Read the source
10. Cochrane Database of Systematic Reviews. Probiotics to prevent infantile colic (Cochrane review summary and abstract). 2019. PMID 30865287, DOI 10.1002/14651858.CD012473.pub2. Read the source
11. BMJ. Treating infant colic with the probiotic Lactobacillus reuteri: double blind, placebo controlled randomised trial. 2014. PMID 24690625, DOI 10.1136/bmj.g2107. Read the source
12. Pediatrics. Lactobacillus reuteri to Treat Infant Colic: A Meta-analysis. 2018. PMID 29279326, DOI 10.1542/peds.2017-1811. Read the source
13. Medicine in Microecology. Efficacy of Lactobacillus reuteri supplementation therapy for Helicobacter pylori eradication: A meta-analysis of randomised controlled trials. 2021. DOI 10.1016/j.medmic.2021.100036. Read the source
14. NIH Office of Dietary Supplements. Probiotics: Fact Sheet for Health Professionals. 2025. Read the source
15. Applied and Environmental Microbiology. Removal of Antibiotic Resistance Gene-Carrying Plasmids from Lactobacillus reuteri ATCC 55730 and Characterization of the Resulting Daughter Strain, L. reuteri DSM 17938. 2008. DOI 10.1128/AEM.00991-08. Read the source
16. Proceedings of the National Academy of Sciences. Host-microbial symbiosis in the vertebrate gastrointestinal tract and the Lactobacillus reuteri paradigm. 2011. DOI 10.1073/pnas.1000099107. Read the source
17. Proceedings of the National Academy of Sciences. Host-microbial symbiosis in the vertebrate gastrointestinal tract and the Lactobacillus reuteri paradigm. 2011. DOI 10.1073/pnas.1000099107. Read the source
18. Proceedings of the National Academy of Sciences. Host-microbial symbiosis in the vertebrate gastrointestinal tract and the Lactobacillus reuteri paradigm. 2011. DOI 10.1073/pnas.1000099107. Read the source
19. Communications Biology. Evaluating the analytical performance of direct-to-consumer gut microbiome testing services. 2026. DOI 10.1038/s42003-025-09301-3. Read the source