Bacillus coagulans (or Lactobacillus sporogenes) and Bacillus subtilis are two spore-forming probiotic bacteria. Some of their benefits: -According to FAO (Food and Agriculture Organization of the United Nations) and WHO (World Health Organization), probiotics are “live microorganisms which, when administered in adequate amounts, confer a health benefit on the host”. -Probiotics must be able to survive through the gastrointestinal tract (which means in an acidic environment and in the presence of bile salts and digestive enzymes), in order to reach and colonize the gut and proliferate. -Probiotic bacteria are safe for human consumption providing a variety of beneficial effects on the host, such as the regulation and maintenance of the gut’s physiological microbiota and the balance of the gut’s homeostasis, the inhibition of pathogens’ and other harmful microorganisms’ colonization and growth, the stabilization of the gastrointestinal tract’s function, the stimulation of immune responses, etc. -They are administered either as a preventive measure or as a therapeutic agent. -Nowadays, spore-forming probiotics, especially of the genus Bacillus, are widely used in humans as dietary supplements. -They are more tolerant to the environmental conditions of the digestive tract and unlike other probiotic bacteria, the entire administered dose of bacilli reaches the small intestine tract without loss. -Moreover, they have the ability to produce anti-microbial substances (bacteriocins), that suppress the growth of intestinal pathogens and other competitive micro-organisms and contribute to the overall better functioning of the intestine even in cases of disorders such as the Irritable Bowel Syndrome (IBS). -Bacillus coagulans and B. subtilis strains have been reported as “safe” by the European Union Food Safety Authority-EFSA (QPS system-Qualified Presumption of Safety) and the U.S. Food and Drug Administration-FDA (GRAS-Generally Recognized Αs Safe). -Bacillus coagulans has been found to be effective against acute diarrhea and abdominal discomfort, but also effective in the management of the clinical symptoms and the depression of IBS patients. -As for Bacillus subtilis, it contributes to the maintenance of the healthy gut microbiota and the stimulation of elderly people’s immune responses.