Probiotics are viable bacteria that beneficially influence the health of the host (I. 2) Probiotic bacteria selected for com- mercial use in fonds and in therapeutics must retain the char- acteristics for which they were originally selected (1-30. These include characteristics for growth and survival during manu- facture and, after consumption, during transit through the stom- ach and small intestine. Importantly, probiotics must retain the characteristics that give ri to their health effects. Conse- quently, it is necessary to test the stability of these characteris- tics during manufacture and storage and to ensure that they are retained in different types of foods (3. 4) The initial screening and selection of probiotics includes testing of the following important criteria: phenotype and genotype stability, including plasmid stability carbohydrate and protein utilization patterns acid and bile tolerance and survival and growth; bile metabo. lism: intestinal epithelial adhesion properties; production of antimicrobial substances; antibiotic resistance patterns; ability