1.Strains for human use are preferably of human origin.
2.They are isolated from healthy human GI-tract.
3.They have a history of being non-pathogenic.
4.They have no history of association with diseases such as infective endocarditis or GI-disorders.
5.They do not deconjugate bile salts (bile salt deconjucation or dehydroxylation would be a negative trait in the small bowel; Marteau et al., 1995).
6.They do not carry transmissible antibiotic resistance genes.
The functional requirements of probiotics should be established by using in vitro methods and the results of these studies should be reflected in controlled human studies. While selecting a preferable probiotic strain several aspects of functionality have to be considered:
1.Acid tolerance and tolerance to human gastric juice.
2.Bile tolerance (an important property for survival in the small bowel).
3.Adherence to epithelial surfaces and persistence in the human GI-tract.
4.Immunostimulation, but no proinflammatory effect.
5.Antagonistic activity against pathogens such as Helicobacter pylori, Salmonella sp., Listeria monocytogenes and Clostridium difficile.
6.Antimutagenic and antigarcinogenic properties.