Various organic solvent and aqueous extracts of Spirulina contain a large variety of micromolecular and macromolecular constituents which express antibacterial activity against a variety of pathogenic microorganisms such as Bacillus subtilis, Streptococcus aureus, Streptococcus faecalis, Staphylococcus epidermidis, Staphylococcus aureus, Proteus vulgaris, Klebsialla pneumonia, Candida albicans, Pseudomonas aeruginosa, Salmonella typhinurium, Mycobacterium smegmatis and Eschericia coli. Spirulina biomolecules with antimicrocrobial activity-include several volatile components and fatty acids. Purified C-phycocyanin from Spirulina platensis was shown to be able to markedly inhibit the growth of drug resistant bacteria Eschericia coli, Klebsiella pneumonia, Pseudomonas aeruginosa and Staphylococcus aureus. Prebiotics are non-digestible food ingredients that stimulate the growth or activity of bacteria in the digestive system, which are beneficial to the health of the body. In this respect it has been found that Spirulina biomass increase the rate of in vitro development of several strains of microorganisms present in fermented dairy products (Lactococcus, Lactobacillus, Streptococcus, Bifidobacterium) and in parallel it expresses beneficial effect on their survival. Moreover, it has been demonstrated that Lactobacillus population in the human gastrointestinal tract is increased by Spirulina consumption.