SCREENING OF ANTIBIOTIC PRODUCING ACTINOMYCETES FOR ANTIBIOSIS FROM SOIL OF SUNSARI, NEPAL

Abstract

Actinomycetes, slow growing gram positive bacteria, are known as an organism that is useful in the search for bioactive compounds. The aim of this study was to screen antibiotic producing Actinomycetes for antibiosis from the soil of Sunsari, Nepal. Primary Screening and Secondary screening were performed by perpendicular streak method and agar well assay method respectively. Microbiological characterization were performed for identification of presumptive genera. Characterization of the antibacterial substances produced by this isolate was done by Thin-layer chromatography (TLC) using Chloroform:Methanol (10:90) as the solvent system and iodine vapor as the visualizing agent. Altogether twenty four actinomycetes were isolated from soil samples but only one (4.2%) of the isolate showed antibacterial activity against both gram positive (Staphylococcus aureus and Bacillus spp.) and gram negative (Escherichia coli, Salmonella Typhi and Pseudomonas spp.) test-bacteria in primary screening. This isolate (S11) was selected for secondary screening because of its potent antibacterial activity. Minimum inhibitory concentration (MIC) of crude antibacterial substances extracted from broth culture of the isolate (S11) was found to be 1.2 mg/ml against test organisms. The chromatogram in TLC showed only one spot with Rf value 0.87 by the isolate suggesting that the isolate produced only one compound which was completely different from the spot with Rf value 0.94 produced by gentamycin. According to identification by Microscopy (1000X) and overall biochemical, and physiological characteristics, the isolate was considered as Streptomyces spp, a distinct taxonomic group