Abstract
Background and Objective: Antimicrobial drug resistance is one of the most serious problems because many bacteria that cause infections are becoming more resistant to the clinically available antibiotics already marketed. Thus, there is an urgent need to discover new antimicrobial agents effective against multi-resistant bacteria. Materials and Methods: The total of 130 morphologically different actinomycete strains were isolated from various soil samples collected from different regions of Egypt and Saudi Arabia and screened for their antimicrobial activities. Streptomyces sp. NEAE-31 was selected for more investigations and identified on the basis of morphological, cultural, physiological and biochemical properties, together with 16S rRNA sequence. Initial screening of fermentation parameters was performed using a Plackett-Burman design and the variables with statistically significant effects on the production of antimicrobial metabolites were identified. The most significant positive independent variables affecting bioactive metabolites production were selected for further optimization studies using face-centered central composite design. Results: The results indicated that Streptomyces sp. NEAE-31 exhibited a broad antimicrobial spectrum against several microorganisms including multidrug-resistant Pseudomonas aeruginosa, E. coli, Staphylococcus aureus, Bacillus subtilis and Bipolaris oryzae. Streptomyces sp. NEAE-31 was identified as Streptomyces lienomycini strain NEAE-31 and sequencing product was deposited in the GenBank database under accession number KF725623. Among the variables screened, yeast extract, CaCO3 and inoculum size had positive significant effects on antimicrobial activities. The maximal antimicrobial activity is 41 mm inhibition zone. Conclusion: The statistical optimization resulted in about 1.64 fold increase in the production of bioactive metabolites by Streptomyces lienomycini strain NEAE-31. The results make this strain attractive for the pharmaceutical industry.