Antimicrobial Activity of Actinomycetes Isolated from Soils in the Brazilian Amazon

Abstract The objective of this work was to evaluate the antimicrobial activity of actinomycetes isolated from soils in the Brazilian Amazon. Soil samples were collected for the isolation of actinomycetes. The actinomycetes were grown in submerged culture and the metabolites extracted in ethyl acetate. The well diffusion method was used to verify the antimicrobial activity of isolated actinomycetes against test microorganisms. The microdilution method was used to determine the minimum inhibitory concentration (MIC) of the extracts against the test microorganisms. Bioautography was used to verify the bioactive compound of the extracts. The biomass and active metabolites were determined. 219 actinomycetes were isolated from Amazonian soils, organized into 153 morphospecies. The most frequent genus were Streptomyces (48.85%) and Nocardia (20.09%). Of the 153 extracts analyzed, 12 (7.84%) had antimicrobial activity, 9 against Gram positive bacteria and 5 against Candida albicans. The MICs of the extracts with activity ranged from 15 to 250 ug/mL. The bioautography method showed that the extracts from Streptomyces 3323 HEX, Streptomyces 3098 DCM, Streptomyces 3333 DCM and Streptomyces 3333 EtOAc generally had an active substance, and that they are different from commercial antimicrobials produced by actinomycetes. Therefore, the actinomycetes from these areas can contribute to the discovery of new antibiotics and the fight against resistant pathogens.