Soil-based organisms (SBO probiotics)

Tier 3 — weak evidence · Gut · Shelf-stable · IBS

Spore-forming bacteria from soil including Bacillus subtilis, B. clausii, and B. licheniformis. Spores survive stomach acid without refrigeration. B. clausii is prescription-strength in some European countries for diarrhoea. However, some SBO products contain poorly characterised strains with limited safety data. Choose products with well-studied, named strains.

Dose: 1–5 billion CFU/day; choose products with named, studied strains (B. clausii, B. subtilis HU58)