Influence of nutritional source in optimum growth and in the production of antibiotics by Streptomyces sp strains

Abstract

The actinomycetes are characterized by their ability to form hyphae, are widely distributed in the environment and well known for the production of biologically active molecules. This study aimed to evaluate the antimicrobial activity of six Streptomyces isolates against nineteen Enterococcus strains. The susceptibility profiles of Enterococcus were evaluated against eleven antibiotics by employing the disk diffusion in agar assay. The antimicrobial activity of the streptomycetes was assessed by means of the double layer method. Isolates which showed activity against the test microorganisms were grown in starch casein broth at 30 °C for seven days, under constant agitation. After growth, the culture was filtered to obtain the crude extract. The antimicrobial activity of the crude extract was evaluated by well diffusion method. The isolate that showed the greatest spectrum of activity was used for growth condition optimization. The isolate was grown in broth medium supplemented with different sources of carbon and nitrogen. The pH of the culture and biomass were determined during all assays period. All Streptomyces strains showed activity against all Enterococcus in the double layer assay. In the well diffusion assay isolate Streptomyces 8S showed the higher antibiotic activity against the test microorganisms. When grown on different carbon and nitrogen sources, the crude extract produced by isolate 8S had better antibiotic activity when grown on starch and potassium nitrate. There was no effect of biomass or the pH in the production of antibiotic molecules.