Antibacterial Effect of Microalgae (Chlorella vulgaris, Scenedesmus obliquus, and Spirulina platensis) Extracts Against Gram-Negative (Escherichia coli, Yersinia ruckeri and Gram-Positive Staphylococcus aureus, Enterococcus faecalis) Bacteria

Abstract

Algae possess antibacterial, antifungal, antiviral, antiparasitic, antioxidant, anticancer properties, serving as a rich source of various bioactive compounds. In this context, the antibacterial activities of the essential oil components of Chlorella vulgaris, Scenedesmus obliquus, Spirulina platensis were investigated in the study. For this purpose, 10% ethanol-methanol was extracted for 48 hours for antibacterial analyses, the solvents were evaporated in a rotary evaporator at 92°C. 10% stock solutions of the obtained algal extracts were prepared with dimethyl sulfoxide. Antibacterial tests were carried out with 10, 5, 1, 0.1% dilutions of stock solutions. The effects of methanol-ethanol dilutions of algae on Gram-negative (Escherichia coli, Yersinia ruckeri), Gram-positive (Staphylococcus aureus, Enterococcus faecalis) have been investigated. For this purpose, disk diffusion, minimal inhibitory concentration, minimum bactericidal medium tests were performed. In addition, 25% methanol extracts were prepared for the analysis of oil components found in algae by gas chromatography-mass spectrometry. As a result, it was determined that only 10% methanol extract of S. platensis had antibacterial activity against S. aureus (zone 15-16 mm), the minimum inhibitory concentration was 8 mg L^-1, the minimum bactericidal concentration was 16 mg L^-1.  It was observed that ethanol-methanol extracts of the other two algae,  ethanol extract of S. platensis, did not have antibacterial activity. A total of 22 essential oil components were found in the algae. The highest oleic acid levels were found in S. platensis at 69.31%, while it showed the highest antibacterial activity only against S. aureus bacterium.