ANTIMICROBIAL ACTIVITY OF SELECTED INDIGENOUS MICROALGAE AGAINST COMMON BACTERIA CAUSING DISEASES IN FISH AND SHELLFISH

Abstract

Antibiotic resistance is recognized as a "One Health subject," comprising human, animal, and environmental interactions, and has become a crucial public health concern. Cyanobacteria, a form of microalgae, recently emerged as one of the most promising sources of natural and eco-friendly antibiotics due to different secondary bioactive compounds. The antibacterial activity of phenolic extracts was assessed using the disk diffusion technique on four strains of Oscillatoria sp. which were isolated from two marine and two freshwater stations in Bangladesh. Three Gram-positive bacteria (Staphylococcus sp. and Streptococcus sp.) and nine Gram-negative bacteria (Escherichia coli, Vibrio sp., Salmonella sp., Shigella sp., Pseudomonas sp., Aeromonas sp.) were isolated from diseased marine fish, Shrimp and Crab and evaluated. Filamentous Oscillatoria sp. indicated higher antibiotic activity than planktonic one. Filamentous Oscillatoria sp. showed the highest inhibition zone 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 (MIC) value was found to be 100µg/ml for filamentous Oscillatoria sp., and 150 µg/ml for planktonic Oscillatoria sp. These findings suggest that, Cyanobacteria contain potential antibacterial substances which could be a better substitute for existing antibiotics and efficiently serve both the aquaculture and pharmaceutical industries. Keywords: