Background. Due to its chemical composition, Spirulina is widely used as a dietary supplement that exerts positive effects on the human body. It also has the ability to inhibit the growth of cert ain microorganisms, both pathogens that pose a health hazard, as well as those that cause food spoilage in all branches of food industry. The main aim of this study was to determine the impact of water extracts of Spirulina (WES) on the growth of various microorganism both useful and harmful for humans and the economy.

Material and methods. The impact of different WES concentrations (0.1, 1.0, 2.5, or 5.0%) on the growth of various bacteria, yeasts and molds was determined by diffusion method on solid medium.

Results. It was demonstrated that WES have a diversifi ed impact on microorganisms, depending on the species. The inhibitory activity was shown against Bacillus subtilis, Micrococcus luteus, Rhodotorula, and Penicillium. WES had strong stimulating effect on Alicyclobacillus acidoterrestris and Geotrichum. Moreover, higher concentrations of WES stimulated also the development of mycelium and production of conidiophores by Cladosporium and Aspergillus niger.

Conclusions. Inhibitory impact of WES on microorganisms that cause food spoilage may be used in food production. However, the obtained results indicate the need for further studies, particularly in order to evaluate the effect of the WES on microfl ora in the food matrices.