Lactobacillus leichmannii

Probiotic

What is it

Lactobacillus leichmannii (now reclassified as Lactobacillus delbrueckii subsp. lactis) is a lactic acid bacterium used historically as a microbiological assay organism for vitamin B12 and as a starter culture in some fermented dairy products.

Evidence for 1 use

AI-assisted evidence assessment — talk to your doctor before relying on any single supplement.

Probiotic / digestive support

Mixed Evidence

Limited clinical evidence specific to L. leichmannii; better-studied lactobacilli have stronger evidence.

How it works

Lactobacillus leichmannii ferments lactose and other sugars to produce lactic acid, contributing to acidification of fermented foods. It has a strict requirement for vitamin B12 (or deoxyribosides), which made it the classical microbiological assay organism for measuring B12 levels in foods, supplements, and clinical samples. As a probiotic supplement, evidence is sparse compared with more thoroughly studied Lactobacillus species (rhamnosus GG, acidophilus, etc.).

Dosage

No established RDA for probiotic intake. Specific dosing for L. leichmannii is not well established; common probiotic dosing is 1-10 billion CFU per day.

When and how to take it

Taken with or just before meals if used as probiotic.

1 commercial form

Compare the main delivery options and what they’re best suited for.

Probiotic preparation

Less common than other Lactobacillus species.

Variable colonization.

Safety

Generally regarded as safe in healthy individuals. Theoretical risk of bacteremia in severely immunocompromised patients.

Who should be cautious

Caution in severe immunosuppression, central venous catheter use, and short bowel syndrome with translocation risk.

Interactions

May interact with antibiotics (reduces probiotic viability). Separate dosing by 2-4 hours.

Food sources

Some fermented dairy products

Amount
varies
%DV
—

Frequently asked questions

Is L. leichmannii a well-studied probiotic?⌄

No, it is more notable historically as a vitamin B12 assay organism than as a probiotic.

Is it safe?⌄

Yes, in healthy people. Caution in severe immunosuppression.

References

Lactobacillus leichmannii on Wikidata — Wikidata link

Lactobacillus leichmannii on NIH DSLD (US supplement label database) — NIH Dietary Supplement Label Database link

Research on Lactobacillus leichmannii (PubMed search) — PubMed link

Track Lactobacillus leichmannii with Pilora

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Evidence-based·How we grade evidence

Disclaimer: These statements have not been evaluated by the FDA. This page is educational, not a substitute for personalized medical advice. Evidence grades are AI-assisted assessments — talk to your doctor before starting any new supplement, especially if you’re pregnant, breastfeeding, on medications, or managing a chronic condition.