Antimicrobial actinomycins isolated by bioautography from Amazonian soil <i>Streptomyces collinus</i> Tü broth

The aim of this study was to isolate and identify bioactive compounds through a bioactivity-guided analysis of extracts from <i>Streptomyces</i> strains. A bioactive extract from a <i>Streptomyces</i> species isolated from Amazonian soil, identified as <i>S. collinus</i> Tü 365 through the 16S rRNA and 23S rRNA genes, was selected for the study. The fermentation broth extract was partitioned and the bioactive fractions were further fractionated using chromatographic techniques (preparative TLC and HPLC). Through bioautography-guided fractionation, two actinomycins (D and X2) were isolated and identified by spectrometric (ESI-HRMSMS) and spectroscopic (NMR) techniques. The isolated substances were tested in the agar disc diffusion assay (<i>Staphylococcus aureus</i>, <i>Streptococcus pneumoniae</i>, <i>Enterococcus faecalis</i> and <i>Escherichia coli</i>) and by the microdilution method in microplates (<i>Staphylococcus aureus</i> and <i>Mycobacterium smegmatis</i>). Actinomycins D and X2 showed activity against <i>M. smegmatis</i> 16.0 μg/mL for both samples and against <i>S. aureus</i>, 1 μg/mL and 0.5 μg/mL, respectively.