Microalgal and cyanobacterial cell extracts for use as natural antibacterial additives against food pathogens

Intra- and extracellular extracts of thirteen cyanobacteria and twelve microalgae were screened for their activity against a few of the most relevant food-borne pathogens - viz. Salmonella sp., Pseudomonas aeruginosa, Escherichia coli and Staphylococcus aureus. Strain M2-1 of Scenedesmus obliquus was the microalga that exhibited the highest antibacterial activity, except against Salmonella sp. Although cyanobacteria possessed in general wider antibacterial spectra than microalgae, the former have also been associated with toxin production - and may thus be less useful in food formulation. Nostoc sp. was particularly effective against E. coli and P. aeruginosa, whereas Gloeothece sp. stood out because of its capacity to inhibit all food pathogens tested. Typically, the intracellular extracts were more powerful than their extracellular counterparts; and those with antibacterial features were found to possess high contents of long chain fatty acids - some of which are well-known for their antibacterial activities.