Antibacterial activity of Streptomyces sp. Y15 against pathogenic bacteria and evaluation of culture media for antibiotic production

Abstract A notable characteristic of Streptomyces bacteria is their ability to produce secondary metabolites. The aims of this study were to identify streptomycetes that exert antibacterial activity against plant and human pathogenic bacteria, and to evaluate antibiotic production in various culture media. To identify streptomycetes that exert broad antibacterial activity using the agar-disk diffusion method, 31 isolates were screened, after which a selected isolate was cultured in nine different growth media to evaluate the production of inhibitory metabolites. Three streptomycete isolates were identified that exert inhibitory activity against at least four pathogens species. The Y15 isolate showed broad antibacterial activity on Escherichia coli, Staphylococcus epidermidis, Listeria monocytogenes, Staphylococcus aureus, Pseudomonas syringae pv. phaseolicola, Dickeya dadantii, and Pectobacterium carotovorum. The production rate of antimicrobial metabolites was maintained when Y15 was grown in culture media containing limited organic nitrogen sources. The presence of organic nitrogen compounds in the media decreased the production of antibacterial metabolites. The Y15 isolate was identified by 16S rDNA gene sequencing as member of the genus Streptomyces. We show that the composition of the fermentation medium is likely an important factor for modulating antibiotic production by streptomycetes, with impacts on the quantity and diversity of antimicrobial metabolites production.