Antibacterial and antifungal activities of selected microalgae and cyanobacteria

Summary In vitro activity of nine cyanobacterial and ten microalgal newly isolated or culture collection strains against eight significant food‐borne pathogens has been evaluated and compared. Water extracts and culture liquids of G loeocapsa sp. and S ynechocystis sp. demonstrated the widest spectrum of activity with minimal inhibitory concentration ( MIC ) ranging from 1.56 to 12.5 mg mL −1 . Culture liquid of A nabaena sp. had the highest activity ( MIC = 0.39 mg mL −1 ) but only to Gram‐positive bacteria. Ethanol extracts and fatty acids from all cyanobacteria and microalgae were active against S treptococcus pyogenes and/or S taphylococcus aureus . The fatty acids of S ynechocystis sp. inhibited the growth of B acillus cereus , E scherichia coli and C andida albicans ( MIC values of 2.5–1.25 mg mL −1 , respectively). Exopolysaccharides ( EPS ) of G loeocapsa sp. were the sample that exhibited activity against all test pathogens with lowest MIC values (0.125–1 mg mL −1 ). High activity with a narrower range of susceptible targets demonstrated the exopolysaccharides of S ynechocystis sp. and R hodella reticulata . Antimicrobial activity was proven for phycobiliproteins isolated from S ynechocystis sp., A rthrospira fusiformis , P orphyridium aerugineum and P orphyridium cruentum , respectively. In conclusion G loeocapsa sp. and S ynechocystis sp. and especially their exopolysaccharides showed the most promising potential against the examined food pathogens.