Actividad antimicrobiana de actinomycetes aislados desde ambientes acuáticos del sur de Chile / Antimicrobial activity of actinomycetes isolated from aquatic environments in Southern Chile

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.

Efecto antibiótico de cepas silvestres de Streptomyces aisladas de suelos chilenos / Antimicrobial effect of wild Streptomyces strains isolated from chilean soils

Background: the solts of the southern part of Chile, that are isolated, cold, humid, poorly axygenated and with a low acitity, could contain new strains of antimicrobial producing Streptomyces strains with antimicrobial activity towards pathogenic bacteria and fungi. Material and methods: two hundred fifty eight soil and sediment samples were collected from 148 paces in Souther regions of Chile. They were cultured in Kuster-Williams growth media and the presence of Streptomyces was confirmed by microscopic examination and biochemical characterization. The antimicrobial activity against reference microorganisms. Results: Seventy seven percent of soils were positive and 542 wild strains of Streptomyces were isolates; of these, 266 had antimicrobial activity. Fifty three percent of isolates had activity against S aureus 43 percent against B subtilis and 0.7 percent against E coli. Most Streptomyces were active against more than one organism. When there was activity against single organisms, these were mostly eucariotic, such as C albicans and T mentagrophytes. Among clinical microorganisms, 29 percent of S aureus strains were inhibited, while P aeruginosa, Alternaria sp, P vulgaris and Y enterocolitica strains were not inhibited. The most frequent Streptomyces morphotypes were those showing pigmented colonies with flexuous and spiral shaped chains of arthopores. Conclusions: soils of the southern region Chile allow the grouth of abundant native strains of Streptomyces with a promising anticrobial activity