Friendly bacteria is the informal, consumer-friendly term for probiotics — live microorganisms, mostly strains of Lactobacillus and Bifidobacterium, that are believed to benefit health when consumed in adequate amounts. They are delivered in fermented foods such as yoghurt, kefir, and kimchi, and in capsules, powders, and fortified products. The idea is that they support the gut microbiota, aiding digestion, crowding out pathogens, and interacting with the immune system. Evidence is strongest for specific strains in specific uses — such as certain probiotics for antibiotic-associated diarrhoea — and weaker for general wellness claims, which regulators police strictly. Products must keep the bacteria alive through shelf life to deliver any effect.