RESUMEN
There is a natural feeling between our intestinal flora and the gut. These microorganisms, living in the various tracts of human intestine, may affect the host homeostasis. Some of these bacteria can perhaps be a source of infection and sepsis when the bowel barrier is physically or functionally breached. The term 'probiotic' dates from the beginning of the last century and in the last years a market for probiotics worldwide, estimated to be worth billions of pounds, has developed. Although there is persuasive advertising for probiotics and there have been methodological advances in the study of the intestinal microbiota, much remains unproven, e.g. how probiotics work, which strains are effective, what can be expected to be achieved, and what dosage is required for effectiveness. This review of the literature is an evidence-based guide through the developing microbial universe affecting our life.