Actinomycetes: Isolation, Characterization and Screening for Antimicrobial Activity from Different Sites of Chitwan, Nepal

With the objective to isolate, identify and determine the antimicrobial activity of the soil actinomycetes, this study was done in the laboratory of Nepal Polytechnic Institute, Chitwan (September 2015- April 2016). A total of 30 soil samples were randomly collected and processed from forest, garden, cultivated lands and river side (Narayani and Rapti River) of Chitwan, Nepal. Isolates were identified by colony characterizations, microscopy and biochemical tests. Primary and secondary screening for antibiotic producers was done by single line cross streak and agar cup assay respectively against test organisms, S. Typhi, S. aureus and E. coli. Altogether 25 different actinomycetes from two genera viz; Streptomyces (n=15) and Micromonospora (n=10) were identified from selected sites (n=10; river side, n=5 each from garden, cultivated and forest soil). Primary screening of n=12 isolates was done by inhibition to at least one test bacterium. Of them only n=9 (n=6 Streptomyces spp., n=3 Micromonospora spp.) isolates showed promising antibacterial activity (zone of inhibition above 8mm) on secondary screening. Maximum zone of inhibition was 14mm observed against S. aureus and whereas 18mm against E. coli and S. Typhi respectively. This finding indicates potent antibiotic producer actinomycetes were isolated from soil of Chitwan, study furthering strain selection and identification would pave the way for commercial antibiotic production