Antibacterial Activity of Isolated Cyanobacteria Species Oscillatoria sp.

Cyanobacteria are a highly diverse group of prokaryotes recognised as a potent source ofbiologically active compounds with antiviral, antibacterial, antifungal, and anticancerproperties. In the present study cyanobacterium Oscillatoria sp. was isolated fromSenanayaka Samudra Reservoir in Sri Lanka and pure monocultures and mass cultures wereprepared. Oscillatoria sp. was harvested after 24 days of incubation at exponential growth toextract compounds using methanol and hexane. Gas chromatography-mass spectrometry(GC-MS) was used to identify compounds present in the crude extract. Antibacterial activityof crude extract was determined by agar well diffusion and disk diffusion methods againstgram positive bacteria of Methicillin-resistant Staphylococcus aureus (MRSA)ATCCm25923 and gram negative bacteria of Pseudomonas aeruginosa ATCC 25853,Salmonella typhii and Escherichia coli ATCC 25922. The results showed that the solventswith different polarities had effects on dry biomass of extracted residue. 10% biomass wasextracted by hexane extraction protocol where 60% of biomass was extracted by methanolextraction. The highest antibacterial activity in methanol extract was detected against S.typhiiin disk diffusion method and the mean diameter of inhibition zone was around 22 mm andmean diameter of inhibition zones of S. aureus, P. aeruginosa and E. coli were recorded as17, 17 and 15 mm respectively within 24 hours. In agar well diffusion method, methanolextract showed the highest antibacterial activity against S. typhii and mean diameter ofinhibition was around 54 mm and mean diameter of inhibition zones of S. aureus, P.aeruginosa and E. coli were recorded as 52, 50 and 52 mm respectively within 24 hours. Inthe hexane extract, antibacterial activities was detected only for S. aureus in both methodsand mean inhibition zones were recorded in 22 and 11 mm for agar well diffusion methodand disk diffusion method respectively within 24 hours. GC-MS analysis revealed that thecrude extract of Oscillatoria contains important fatty acid compounds such as hexadecanoicacid (palmitic acid methyl ester), methyl tetradecaoate (myristic acid methyl ester) and 13-Tetradecanoic acid (methyl ester) which possesses antibacterial and antifungal properties.Thus, the result of the study showed that the Osillatoria contained compounds which arepotential for pharmaceutical invention.Keywords: Oscillatoria sp. Antibacterial compounds, Well diffusion, Disk diffusio