The Effect of Salinity Stress on the Antibacterial Activity of Spirulina Platensis Algae

Background: The production of secondary metabolites in different strains of microalgae varies and is likely dependent on environmental conditions. Consequently, the production of bioactive substances as secondary metabolites occurs in microalgae to aid their survival in adverse environmental conditions such as salinity stress. Objectives: The purpose of this study is to investigate the antibacterial activity of the methanolic extract of Spirulina platensisalgae cultivated under different salinity stresses against Yersinia rukeri, Escherichia coli, Salmonellasp and Vibrio cholerae. Methods: The broth microdilution method was used to evaluate the growth inhibitory activity of the extracts against Yersinia ruckeri, Salmonellasp Escherichia coli, and Vibrio choleraebacteria. The minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) were determined by this method, and the diameter of the inhibition zone was assessed through the well diffusion method. Results: In the treatment with algae extract grown under 3.5 ppt salinity stress, the concentrations of 50 and 25 mg/mL extract showed the largest inhibition zone diameter against Salmonellasp. compared to other bacteria. Under 7 ppt salinity stress, all studied concentrations of algal extract exhibited a higher inhibition zone diameter against V. choleraecompared to other bacteria. The results of comparing different concentrations of algae extract between the two salinity stresses of 3.5 and 7 ppt for each bacterium showed a significant difference (P 0.05). As salinity increased, the diameter of the inhibition zone also increased for all bacteria. Conclusions: Our results showed an increase in the antibacterial activity of the methanolic extract of Spirulina platensiswith higher salinity stress levels. Therefore, cultivating Spirulinaalgae in salt water can be a cost-effective and suitable method to produce more secondary metabolites for use in the pharmaceutical industry.