In vitro antibacterial activity of bioactive metabolite and crude extract from a new streptomyces strain Streptomyces rajshahiensis

A new strain of Streptomyces identified as Streptomyces rajshahiensis (RUPA08-PR) was isolated from the soil of Rajshahi, Bangladesh. Ethyl acetate was the most convenient solvent for the extraction of antimicrobial metabolites from the culture filtrate of this strain. From the ethyl acetate extract compound 1 was isolated, purified and characterized by spectral data. The compound showed antibacterial activity against a number of both Gram positive and Gram negative bacteria but did not have antifungal activity. The minimum inhibitory concentration (MIC) of the compound 1 and ethyl acetate extract was determined against four Gram positive and four Gram negative bacteria and the values were found between 32 and 128 mg/ml. Both the isolated compound 1 and the ethyl acetate extract exhibited cytotoxic effect in brine shrimp lethality bio-assay with LC50 values of 1.32mg/ml and 0.89mg/ml respectively.