Antibacterial Activity of Isolated Cyanobacteria Species Oscillatoria sp.

Abstract

Cyanobacteria are a highly diverse group of prokaryotes recognised as a potent source of
biologically active compounds with antiviral, antibacterial, antifungal, and anticancer
properties. In the present study cyanobacterium Oscillatoria sp. was isolated from
Senanayaka Samudra Reservoir in Sri Lanka and pure monocultures and mass cultures were
prepared. Oscillatoria sp. was harvested after 24 days of incubation at exponential growth to
extract compounds using methanol and hexane. Gas chromatography-mass spectrometry
(GC-MS) was used to identify compounds present in the crude extract. Antibacterial activity
of crude extract was determined by agar well diffusion and disk diffusion methods against
gram 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 solvents
with different polarities had effects on dry biomass of extracted residue. 10% biomass was
extracted by hexane extraction protocol where 60% of biomass was extracted by methanol
extraction. The highest antibacterial activity in methanol extract was detected against S.typhii
in disk diffusion method and the mean diameter of inhibition zone was around 22 mm and
mean diameter of inhibition zones of S. aureus, P. aeruginosa and E. coli were recorded as
17, 17 and 15 mm respectively within 24 hours. In agar well diffusion method, methanol
extract showed the highest antibacterial activity against S. typhii and mean diameter of
inhibition 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. In
the hexane extract, antibacterial activities was detected only for S. aureus in both methods
and mean inhibition zones were recorded in 22 and 11 mm for agar well diffusion method
and disk diffusion method respectively within 24 hours. GC-MS analysis revealed that the
crude extract of Oscillatoria contains important fatty acid compounds such as hexadecanoic
acid (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 are
potential for pharmaceutical invention.
Keywords: Oscillatoria sp. Antibacterial compounds, Well diffusion, Disk diffusion