Antimicrobial activities of indigenous trees associated rhisosphere Actinomycetes, southwest Ethiopia

Abstract

Actinomycetes are gram positive bacteria that widely serve as source of novel antimicrobial substance. This study was designed to evaluate antimicrobial activities of actinomycetes isolated from soil in Bada Buna. The study was conducted at Bada buna forest. Rhizospehre soil of indigenous plants of natural Bada Buna natural forest were selected purposively following purposive sampling technique. Then, twenty five soil samples were collected. For laboratory analysis, ten gram of each soil sample was taken in sterilized Erlenmeyer flask containing 90ml of normal saline solution (0.85%) and shaken on rotatory shaker (160rpm) for about5 minutes. The pure cultures were screened for antimicrobial activities by inoculating the pure culture into starch casein broth for fourteen days after which it was centrifuged at 10,000 rpm for 20 minutes. The supernatant was check for antimicrobial activities using disc diffusion and agar well diffusion method. In the present study, 60 actinomycetes were isolated out of which twelve (20%) showed antimicrobial activity against one or more human pathogenic test bacteria and fungus. Among a total of twelve isolates 6 (50%) actinomycetes showed antimicrobial activities both on gram positive and gram negative bacteria,5(41.66%) of the isolates showed antimicrobial activities against only gram negative bacteria and 1(8.33%) the isolate showed antimicrobial activities against gram positive bacteria. Four (33.3%) isolates showed antimicrobial activities on C.albicans (ATCC14053).Of the twelve isolates that displayed antimicrobial activity, 6 isolates were further screened for submerged fermentation based on their activities. Except isolate AC10, all the crude extracts of isolate exhibited antimicrobial activity against all the test organisms during secondary screening process. The isolates were identified and characterized by morphological, physiological, and biochemical characteristics. From the present study it could be conclude that rhizosphere soil could be potential source of antibiotic producing actinomycetes. Further work needs to carried out in details and the isolates identified up to species level by using molecular characterization.