Recommended Limosilactobacillus reuteri Strains
For probiotic use, the recommended strains of Limosilactobacillus reuteri are DSM 17938 or ATCC 55730, with the strongest evidence supporting their use in preterm infants for prevention of necrotizing enterocolitis (NEC).
Clinical Context and Strain-Specific Recommendations
The 2020 AGA Clinical Practice Guidelines explicitly identify L. reuteri DSM 17938 or ATCC 55730 as evidence-based strains for specific clinical applications 1. These are not interchangeable with other L. reuteri strains—probiotic effects are strain-specific and each requires individual assessment.
Primary Indication: Preterm Infants (<37 weeks gestational age)
L. reuteri (DSM 17938 or ATCC 55730) is conditionally recommended for preventing NEC in preterm, low-birth-weight infants, supported by moderate to high-quality evidence 1. The evidence demonstrates:
- Reduction in severe NEC (stage II or greater): OR 0.55,95% CI 0.34–0.91 1
- Shortened hospitalization: mean difference –7.89 days (95% CI –11.60 to –4.17) 1
- Reduced time to full enteral feeds: mean difference –2.62 days (95% CI –4.53 to –0.71) 1
Secondary Applications with Emerging Evidence
For antibiotic-associated diarrhea (AAD) in children, recent 2026 data suggests L. reuteri DSM 17938 may reduce AAD risk when:
- Administered for up to 21 days (RR 0.50,95% CI 0.33–0.75, moderate certainty) 2
- Used specifically with amoxicillin-clavulanate (RR 0.49,95% CI 0.32–0.76) 2
However, no benefit was found with ≤14-day administration or extended follow-up, limiting routine recommendation 2.
For ulcerative colitis in children, rectally administered L. reuteri ATCC 55730 showed increased clinical response (RR 1.83,95% CI 1.14–2.92), though this was a single study with very low certainty evidence 1.
Critical Caveats
Safety Considerations
- Avoid in severely ill or immunosuppressed patients who place high value on harm avoidance, as harms reporting remains inconsistent across studies 1
- The strain has demonstrated excellent safety even at higher dosages in multiple trials 3
What NOT to Use L. reuteri For
- Acute gastroenteritis in North American children: The AGA explicitly recommends AGAINST probiotics for this indication, based on large multicenter RCTs showing no benefit 1
- Maintenance of ulcerative colitis remission: Insufficient evidence 1
- Treatment of C. difficile infection: Significant knowledge gap identified 1
Practical Implementation
When prescribing L. reuteri, specify the exact strain (DSM 17938 or ATCC 55730) on the prescription, as:
- Product manufacturing details vary significantly between formulations 1
- Strain-specific effects cannot be generalized to other L. reuteri strains 2, 3
- Commercial availability may differ by region
The mechanism of action involves reuterin production, antimicrobial effects, gut microbiota modulation, and enhanced tight junction protein expression 3, 4, 5, but these benefits are not guaranteed with unstudied strains.