Probiotics are live microorganisms that confer a health benefit to the host when consumed in adequate amounts.
Mechanisms and health effects of probiotics
Probiotic organisms such as Lactobacillus, Bifidobacterium and the yeast Saccharomyces boulardii are normal inhabitants of the human gut or are closely related to commensal microbes. They are chosen because they can survive gastric acid and bile salts, transiently colonize the intestine and interact with mucosal immune cells. When ingested in sufficient numbers, they compete with pathogens for nutrients and adhesion sites, produce organic acids and bacteriocins that suppress harmful bacteria, and modulate epithelial barrier function. Some strains enhance secretion of mucins and defensins, stimulate regulatory T cells and influence systemic inflammation. These properties underlie their use in preventing antibiotic‑associated diarrhoea, reducing the incidence of necrotizing enterocolitis in premature infants and alleviating symptoms of irritable bowel syndrome. The benefits are strain‑specific and depend on dose, viability and the health status of the recipient.
Representative species and uses
Common probiotic strains include Lactobacillus rhamnosus GG, L. acidophilus, Bifidobacterium animalis subsp. lactis BB‑12 and S. boulardii. They are delivered in fermented dairy products, fermented vegetables, capsules or powders. In double‑blind trials, S. boulardii reduced recurrence of Clostridioides difficile infection and traveller’s diarrhoea. L. rhamnosus GG improves recovery from acute rotavirus gastroenteritis in children and shortens respiratory infection episodes. Probiotic yogurts may aid lactose digestion by providing β‑galactosidase. Some synbiotic products combine probiotics with prebiotic fibres to enhance colonization. While generally safe, bloodstream infections have been reported in severely immunocompromised patients, and regulatory oversight varies by country.
The concept of probiotics underscores the importance of maintaining a balanced microbiota for human health. Specific strains can influence digestive, immunologic and metabolic processes, but they are not universally beneficial and should be selected based on evidence.
Related Terms: Microbiome, Prebiotics, Synbiotics, Lactobacillus, Gut Flora