The antibacterial activity of phenolic extracts was assessed using the disk diffusion technique on two marine and two freshwater species of Oscillatoria. Three Gram positive bacteria (Staphylococcus sp. and Streptococcus sp.) and nine Gram negative bacteria (Escherichia coli, Vibrio spp., Salmonella sp., Shigella sp., Pseudomonas spp., Aeromonas sp.) were isolated from diseased marine fish, shrimp and crab. Filamentous Oscillatoria sp. indicated higher antibiotic activity than planktonic one. Gram positive bacteria showed higher susceptibility to phenol compared to the gram-negative bacteria. Filamentous Oscillatoria sp. showed highest inhibition zone of 34.06 ± 0.08mm against Staphylococcus sp., while planktonic Oscillatoria sp. showed lower inhibition zone against Pseudomonas sp. about 17.11 ± 0.18mm. Minimum inhibitory concentration value was found to be 100 µg/ml for filamentous Oscillatoria sp., 150 µg/ml for planktonic Oscillatoria sp. These findings suggest that, Oscillatoria spp. contain potential antibacterial substances. It also paves the way for detailed analysis of Oscillatoria spp. bioactive compound for the creation of novel antibiotics and serve both the aquaculture and pharmaceutical industries.
Keywords: Activity index; Antimicrobial activity; Cyanobacteria; Minimum inhibitory concentration; Oscillatoria; Pathogenic bacteria.
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