Table 2.

Selection criteria for probiotic strains

Criteria	Required properties
Safety	Human or animal origin Isolated from the gastrointestinal tract of healthy individuals History of safe use Precise diagnostic identification (phenotype and genotype traits) Absence of data regarding an association with infective disease Absence of the ability to cleave bile acid salts No adverse effects Absence of genes responsible for antibiotic resistance localized in non-stable elements
Functionality	Competitiveness with respect to the microbiota inhabiting the intestinal ecosystem Ability to survive and maintain the metabolic activity, and to grow in the target site Resistance to bile salts and enzymes Resistance to low pH in the stomach Competitiveness with respect to microbial species inhabiting the intestinal ecosystem Antagonistic activity towards pathogens Resistance to bacteriocins and acids produced by the endogenic intestinal microbiota Adherence and ability to colonize some particular sites within the host organism An appropriate survival rate in the gastrointestinal system
Technological usability	Easy production of high biomass amounts and high productivity of cultures Viability and stability of the desired properties of probiotic bacteria during the fixing process High storage survival rate in finished products Guarantee of desired sensory properties of finished products Genetic stability Resistance to bacteriophages