Screening of terrestrial actinomycetes for antimicrobial activity isolated from Kodagu District, Karnataka State in India

2016 
Actinomycetes are valuable potent prokaryotes produce diverse range of bioactive compounds like antibiotics. Isolation and screening of actinomycetes for antimicrobial activity as well as identification of the most potent bioactive isolates from the unexplored soil of Western Ghats of Kodagu district, Karnataka, India was the aim of the present study. A total of 158 actinomycetes were isolated from three different localities of Kodagu district by serial dilution method. All the isolates were subjected to primary screening to evaluate antimicrobial activity against test microorganisms by perpendicular streak method. Based on the primary screening, 58 isolates showed noticeable antimicrobial activities and were selected for secondary screening by Kirby Baure diffusion method. Among 58 potent isolates, 22.41 % showed activity against Staphylococcus aureus, 18.96 % against Bacillus subtilis, 15.51 % against Escherichia coli, 17.24 % against Enterobacter aerogenes, and 8.62 % against Aspergillus niger respectively. Upon primary and secondary screening, 4 isolates which showed broad spectrum antibacterial activities against both Gram-positive and Gram-negative bacteria (ACTK 2.3.1, ACTK4.2, ACTM15.2 and ACTM 8.3) were identified as Streptomyces spp. by cultural, morphological, biochemical and chemotaxonomic characteristics. Extraction of antimicrobial compounds from these four potent isolates by liquid-liquid extraction method with different organic solvents showed that there was a significant difference across the solvents used (p � 0.05). Among the crude extracts, n-butanol extract from the isolate ACTK2.3.1 was the most effective which showed maximum antibacterial activity. Finding reveals the kodagu's terrestrial environment could be a promising source for novel actinomycetes and their potent antibiotics.
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