VITAMINS & SUPPLEMENTS · GUIDE
Lactobacillus vs Bifidobacterium vs Saccharomyces boulardii: Different Organisms, Different Evidence
Lactobacillus and Bifidobacterium are bacteria, Saccharomyces boulardii is a yeast; each has strain-specific evidence and different cautions, and none wins across the board.
Content last updated . This page has not been medically reviewed.
Back to Probiotics & Gut SupportLactobacillus and Bifidobacterium are groups of bacteria. Saccharomyces boulardii is a yeast. The NCCIH puts it plainly: different probiotics may have different effects, and if one kind of Lactobacillus helps prevent an illness that does not mean another Lactobacillus or any Bifidobacterium would do the same.[1] So there is no universal winner, and the useful question is always "which strain, for which condition, in which people?"
Names you may meet
In 2020 researchers proposed splitting the old genus Lactobacillus into 25 genera, including new names such as Lacticaseibacillus, Limosilactobacillus and Lactiplantibacillus. The emended genus Lactobacillus keeps species such as L. acidophilus, and "lactobacilli" remains a handy general term.[2] Many trials and labels still use the old names, so this page uses the names as each source did.
Evidence labels used below: promising but limited, mixed, insufficient evidence and Proper evidence not found.
Side by side
| Lactobacillus and relatives | Bifidobacterium | Saccharomyces boulardii | |
|---|---|---|---|
| What it is | Bacteria[1] | Bacteria[1] | Yeast, described as a non-bacterial microorganism[3] |
| Documented evidence | A systematic review found strain-specific efficacy for preventing adult antibiotic-associated diarrhea within some Lactobacillus products, while other Lactobacillus strains showed none.[4] | A 2014 review of constipation trials in adults found some benefit, especially for Bifidobacterium lactis; a 2017 review in older people found a small benefit, mostly with Bifidobacterium longum; a 2017 review in children found none for the probiotics tested.[1] | A meta-analysis of 21 trials (4,780 people) found antibiotic-associated diarrhea fell from 18.7% to 8.5% with S. boulardii versus placebo or no treatment.[5] |
| Strength | Mixed: depends on the strain and the use | Mixed: small reviews, varied products | Promising but limited: many trials, but they used varying products and definitions |
| Specific caution | Same general cautions as all live products | Same general cautions; strains differ in how well they survive storage[6] | Reported bloodstream fungal infections (fungemia) in seriously ill or older people[7] |
Bacteria versus yeast: what is actually different
Because S. boulardii is a yeast, antibiotics are not aimed at it. One review notes it is intrinsically resistant to antibiotics and cannot promote the spread of antibiotic resistance.[3] A 2024 review adds that, unusually for a probiotic, it is a eukaryote and so not directly affected by antibiotics.[8]
The other side of the coin is fungemia. A retrospective hospital review (2005 to 2017) of S. cerevisiae fungemia called it rare but life-threatening and associated with S. boulardii-containing probiotics (six of the 10 patients had been prescribed one); 80% of the 10 patients were on tube or intravenous feeding, 70% had a central venous line, and half died.[7] In an intensive care unit, seven patients developed S. boulardii fungemia, and the authors did not recommend using it in critically ill patients.[9]
Head-to-head: little to rely on
We found one direct comparison: a non-randomized hospital study in Lahore of 200 children aged 6 months to 5 years with acute diarrhea. Complete resolution was 95% with bacterial probiotics (Bifidobacterium and Lactobacillus) and 87% with a yeast probiotic. Because children were not randomly assigned and the exact strains were not given in the abstract, this cannot show that one type is better.[10] The Cochrane review of probiotics for acute infectious diarrhea found, in the studies at low risk of bias, little or no difference in diarrhea lasting 48 hours or longer, including analyses limited to Lactobacillus rhamnosus GG and S. boulardii.[11] Proper evidence not found for a large randomized trial of Lactobacillus versus Bifidobacterium versus S. boulardii in the same condition; we searched PubMed for head-to-head comparisons.
Where to read more
Frequently asked questions
Is S. boulardii better than Lactobacillus for antibiotic diarrhea?
Both have strain-specific evidence. A 2018 review found efficacy within some Lactobacillus products and for S. boulardii CNCM I-745, varying by disease.[4] No large direct comparison was found.
Why is S. boulardii often mentioned with antibiotics?
It is a yeast, so antibiotics do not act on it directly, according to a 2024 review.[8]
Does the name Lactobacillus still apply to my product?
Possibly not. Since 2020 many species have new genus names, but labels and trials often keep the old ones.[2]
Who should avoid S. boulardii?
The reports we read involve seriously ill people, those with central lines, and older patients; one review of fungemia suggested older age should be a contraindication. Ask a clinician.[7]
Can I pick a type from its genus alone?
No. Results belong to a specific strain, product and group of people.[1]
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
Safety and who should ask first
The risk of harm from any probiotic is greater in people with severe illness or compromised immune systems, and the FDA has warned about premature infants.[1] Antibiotic-associated diarrhea reviews in children found no serious adverse events attributable to probiotics in 24 trials, though observational reports describe serious events in debilitated or immunocompromised children with central venous catheters.[12] Ask a clinician or pharmacist before starting one if you take immune-suppressing or antifungal medicines; see Medication Interactions and Probiotic Safety.
Severe or bloody diarrhea, signs of dehydration or illness in a young child need medical care, not a supplement. The NHS lists bloody diarrhoea and signs of dehydration among reasons to seek urgent advice.[13]