Screening for Antibacterial Activity of Streptomyces Species Isolated from Zanjan Province, Iran

Introduction: The Streptomyces genus is well studied owing to its capacity in producing more than 70% of antibiotics. This study was undertaken to characterize Streptomyces strains occurring in soils of Zanjan province, Iran as well as to evaluate their potential to produce antimicrobial compounds. Methods: Samples were collected from agriculture and Nonagriculture zones. In primary screening by agar overlay method, Streptomyces strains were assessed for antibiotic production and activity against four bacteria including Escherichia coli, Salmonella typhi, Staphylococcus aureus and Pseudomonas aeruginosa. Then active isolates were selected for secondary screening by microplate MIC. Then, 16S rRNA PCR was carried out for confirmation of isolates. Results: In primary screening among all of the isolates, 154/229 (67.24%) isolates were active against at least one of the test organisms and 20/229 (8.7 %) strains exhibited a broad-spectrum activity against both test bacteria. The minimum inhibitory concentrations (MICs) of the ethyl acetate extracts ranged from 0.78-200 μg/mL and the least minimum bactericidal concentration (MBC) demonstrated was 12.5 μg/ml against strain Staphylococcus aureus. 16S rRNA gene for two more active strains was sequenced and submitted to GenBank. Conclusion: These results highlight the importance of streptomyces isolates in antibiotic production