Antibacterial activity of two cyanobacterial strains i.e. Nostoc ellipsosporum NDUPC002 and Nostoc sp. NDUPC003 was studied. Both cyanobacterial strains were isolated from agricultural fields of Varanasi, India. Crude extracts of both strains in five solvents i.e. Ethanol, Petroleum ether, Acetone, Methanol, and Chloroform was screened against two human pathogenic bacteria i.e. S. aureus and E. coli. Crude extracts of each strain show differential antibacterial response to test organisms. Crude extract in organic solvents i.e. Ethanol, Petroleum ether, Methanol and Acetone of Nostoc ellipsosporum NDUPC002 showed antibacterial activity against S. aureus where as the extract in Petroleum ether and Methanol only showed antibacterial activity against E. coli. Ethanol extract of Nostoc ellipsosporum NDUPC002 showed the maximum antibacterial activity of 12.67±0.58 mm against S. aureus. Crude extract, only in three organic solvents i.e. Ethanol, Methanol & Acetone of Nostoc sp. NDUPC003 showed antibacterial activity against S. aureus and E. coli with maximum antibacterial activity (6.0±0.42 mm) in acetone extract against E. coli. Findings of the experiment suggest that ethanol extract of Nostoc ellipsosporum NDUPC002 can be used for mining of antibacterial agent against S. aureus.
