Antibacterial activity of organic fractions from freshwater microalga Chlorella vulgaris against fish and shellfish pathogens

Abstract

The ethanol-based crude extract and fractions partially purified from the freshwater microalga, Chlorella vulgaris underwent screening using disc diffusion assays. The tube dilution method was also employed to determine the minimum inhibitory concentration (MIC) values. The screening involved testing a variety of Gram negative bacterial fish and shellfishpathogens. The panel of pathogens included four strains of Aeromonas hydrophila (AH1, AH2, AH3, AH4), two strains of Pseudomonas putida (PP1, PP2), two strains of Pseudomonas aeruginosa (PA1, PA2), two strains of Pseudomonas fluorescens (PF1, PF2), Escherichia coli (O115, O1, O156, O164, O111 and O109), Vibrio alginolyticus (VA), V. anguillarum (VAN), V. fluvialis (VF), V. parahaemolyticus (VP), V. harveyi (VH), V. fisheri (VFS), and Edwardsiella tarda.The crude ethanolic extract underwent partial purification through silica gel column chromatography.The crude ethanolic extract was potentially active against all the selected bacterial pathogens, with the lowest MIC value (300 μg) against P. aeruginosa (PA2) and E. coli (O1, O156, O109). Among the nine chromatographic fractions, three exhibited higher activity with lower MIC values (40-50 μg). The results indicate that partially purified C. vulgaris extract has superior antibacterial activity compared to the crude extract. It could be a viable alternative for managing bacterial pathogens in aquaculture, potentially curbing the rise of antibiotic resistance. Keywords: Antibacterial, Chlorella vulgaris, Minimum inhibitory concentration, Pathogen, Vibrio