Antimicrobial Activity of Microalgae and Medicinal Plants against Common Bacteria Causing Diseases in Fish and Shellfish

Abstract

Antimicrobial activity of the ethanolic extract of dried marine microalgae Chlorella sp., and Spirulina sp. and dried medicinal plant Aloe vera (A. vera) and Clinacanthus nutans (C. nutans) were studied against three Gram-negative bacteria Aeromonas hydrophila, Vibrio sp., Escherichia coli and one Gram-positive bacteria Staphylococcus saprophyticus isolated from local fish, shrimp and crab by using disk diffusion technique. In this study, Spirulina sp. showed the highest inhibition zone of 19.3±0.577 mm against Vibrio sp. isolated from crab, whereas Chlorella sp. exhibited a maximum inhibition zone of 11.41±0.65 mm against S. saprophyticus. C. nutans displayed antibacterial activity against S. saprophyticus and E. coli with the maximum zone of inhibition (14.21±1.075; 15.103±0.214 mm), whereas A. vera against E. coli, Vibrio sp. with significant inhibition zone (14.037±0.903; 15.363±1.11 mm) respectively. The Minimum Inhibitory Concentration (MIC) of the extracts was determined against the test bacteria and the lowest concentration was revealed by Chlorella sp. at 20 mg/ml against all the test bacteria. MIC value of the Spirulina sp., A. vera, and C. nutans was recorded from 20 mg/ml to 40 mg/ml against the test bacteria. These results indicate the presence of promising antibacterial compounds in the plants and microalgae studied. Further phytochemical studies are needed to elucidate the active component responsible for the antibacterial activity of these extracts.