Figure 1
Large-scale screening strategy of secondary metabolites for mining agents that enhance the action of polymyxin B.
A to F. Schematic representation of each experimental procedure to identify and characterize compounds that show synergism with polymyxin B. (a) Isolation of various Streptomyces spp. from different soil environmental samples. (b) Isolation of secondary metabolites from individual Streptomyces spp. (c) Mass screening of metabolites with serial concentrations of polmyxin B (250, 25, 2.5 and 0 mg/L), as indicated by violet color shades. Tetrazolium dye (0.5%) is included along with media, to measure the E. coli susceptibility to combined action of secondary metabolite and polymixin B. (d) Identification of synergetic compounds that originated from selected metabolite using 16 s rDNA sequencing and analytical chemistry techniques to identify compound within the metabolite responsible for synergism. (e) Checkerboard assay to test synergistic activity of compounds present in secondary metabolites against various Gram-negative pathogenic bacteria. (f) In vivo time kill assay using the greater wax moth to verify the effectiveness of combination therapy. Bacterial strains were infected to G. mellonella larvae followed by administration of polymixin B or netropsin or both.
