ABSTRACT
Background: The easy access and inappropriate use of antimicrobials led to selection and spread of resistant microorganisms strains. It is imperative to search for new and more effective antimicrobials. One strategy is the screening of metabolites produced by microorganisms found in the environment. Actinomycetes are a potential source of new drugs. Aim: To isolate actinomycetes from sediments of Chilean rivers and lakes and to screen them for antimicrobial activity against reference bacterial strains and pathogenic fungi. Material and Methods: Actinomycetes were isolated from sediment samples, using casein-starch agar. The antimicrobial activity against 3 bacterial species and 7 fungal species was tested using the disc diffusion method. For the extraction of active metabolites, culture broths of antagonistic actinomycetes were extracted with organic solvents followed by testing the antibiotic activity. Results: A total of 62 strains of actinomycetes were isolated, mainly Streptomyces sp (83.9 percent). Thirty six strains (58.1 percent) showed antimicrobial activity, mainly against Bacillus subtilis and Candida albicans. Some isolates inhibited a wide spectrum of indicator strains, like LRI 4A strain (Streptomyces sp) that inhibited Bacillus subtilis, Candida albicans and 4 filamentous fungi. Conclusions: Lakes and rivers of Southern Chile are an important reservoir of antagonistic actinomycetes, a potential source of new drugs.