Antimicrobial effect of yeast isolated from kefir

The aim of this study was to investigate the antimicrobial effects of yeasts isolated from kefir on some pathogenic microorganisms. Firstly, yeasts were isolated from commercial kefir samples and kefir beverages prepared from kefir grains. Then, antimicrobial activity of yeast isolates against Aspergillus flavus, Aspergillus niger, Escherichia coli and Staphylococcus aureus were investigated by using spot-inoculatd and/or well diffusion methods. In the spot-inoculated method, the zone diameter that indicate the antimicrobial effect against molds was not determined, however sporulation was decreased. In the well diffusion method, the zone diameter against bacteria determined as <1 mm. Finally, the antibacterial effect of yeast isolates against E. coli and S. aureus by microdilution method was examined by optical density measurement at 2-hour intervals during 24 hours. According to the results of microdilution method, isolated yeasts had limited antimicrobial effect against E. coli and S. aureus. On the other hand, yeast isolates had a higher antibacterial activity against S. aureus then E. coli.