Probiotics and Prebiotics

Definitions & overview

• Rationale — Diarrhoeal illness and antibiotic use disturb the population, composition and balance of the gut microflora; recolonising the gut with non-pathogenic, mostly lactic-acid-forming bacteria and yeast is believed to help restore that balance — the conceptual basis of probiotic/prebiotic therapy.
• Microbiome vs microbiota — The microbiome is the genetic repertoire of the microbial ecosystem at a body site; the microbiota is the collection of microbes itself. Microbial genes outnumber human genes ~10⁴-fold and microbial cells exist in ~1:1 ratio with human cells; >90% of gut microbiota are Bacteroidetes & Firmicutes.
• Probiotic — "Live microorganisms that, when administered in adequate amounts, confer a health benefit on the host" (FAO/WHO 2001/2002; reaffirmed ISAPP 2014). Three implicit criteria — viable at administration, a defined adequate dose (CFU), and a measurable benefit in a controlled study. [PMID 24912386]
• Prebiotic — "A substrate that is selectively utilized by host microorganisms conferring a health benefit" (ISAPP 2017) — prototypes are the fermentable carbohydrates inulin, fructo-oligosaccharides (FOS), galacto-oligosaccharides (GOS) and lactulose. [PMID 28611480]
• Synbiotic — "A mixture of live microorganisms and substrate(s) selectively utilized by host microorganisms" (ISAPP 2019) — a complementary synbiotic co-formulates an evidenced probiotic + evidenced prebiotic; a synergistic synbiotic pairs a substrate designed to be used by the co-administered microbe. [PMID 32826966]
• Postbiotic — "A preparation of inanimate microorganisms and/or their components that confers a health benefit" (ISAPP 2021) — deliberately excludes purified metabolites (isolated butyrate), vaccines, cell-free filtrates lacking biomass, phages and synthetic compounds. [PMID 34002101]
• Spectrum of intervention — Narrowest → broadest defined-organism content: purified prebiotic substrate → single-strain probiotic → defined multi-strain consortium → undefined whole-community FMT.