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Actinobacteria strains isolated from coil mining soil of Bechar region, Algeria, were evaluated for their antimicrobial potential against pathogenic germs particularly against uropathogenic multiresistant Escherichia coli ST131. Of the 119 isolates, 82 exhibited potent antimicrobial properties. The strain that showed maximum inhibition against E. coli ST131 was further screened toward nine bacterial pathogens and identified based on morphological, physiological and 16S rRNA gene sequencing. The isolate was related to the genus Streptomyces with 99.46% sequence similarity to Streptomyces klenkii strain S2704T and assigned as Streptomyces sp. CMB51. To achieve maximum metabolites production, significant process parameters were optimized through response surface methodology employing Plackett–Burman and Central Composite designs. In PBD experiments, starch and casein concentrations, incubation time and initial pH value emerged as the most significant affecting the output of anti-E. coli ST131 activity. The composition of the final optimized medium was soluble starch concentration of 5.31 g/L, casein concentration of 0.45 g/L, 3 days incubation time and 8.41 initial pH value. The optimization resulted an antibacterial activity of 13 mm which was in close accordance with the predicted value of 13.60 mm recording 18.18% increase. The chosen method was efficient for further investigations of the production of anti-E. coli ST131 metabolites. [ABSTRACT FROM AUTHOR]

Streptomyces thermoviolaceus SRC3, a newly isolated actinobacterial strain from Algerian river sediments, exhibited a broad activity against various bacterial and yeast human pathogens (Salmonella Typhi ATCC 14028, Vibrio cholerae ATCC 14035, MRSA ATCC 43300 and Candida albicans ATCC 10231). The strain SRC3 was selected from thirty nine actinobacterial isolates and identified as S. thermoviolaceus based on morphology, cultural properties, physiological analyses and 16S rRNA gene sequencing. Culture parameters for the antibiotic production were optimized by sequential statistical strategy including Plackett-Burman design (PBD) and Response Surface Methodology (RSM). In PBD experiments, KCl, K 2 HPO 4 , MgSO 4 ·7H 2 O, pH value and incubation time emerged as the most significant in affecting the output of antimicrobial activities. These factors were further optimized using Central Composite Design (CCD). The best achieved conditions were: KCl (0.01%), K 2 HPO 4 (0.1%), MgSO 4 ·7H 2 O (0.02%) and 9 days incubation for anti-S. Typhi compounds, KCl (0.051%), MgSO 4 ·7H 2 O (0.05%) and 5 days incubation for C. albicans inhibitors. The metabolite responsible for the bioactivities was purified, structurally characterized (by NMR, MS, UV and IR analyses) and identified as streptazolin, recently reported as a promising antibiotic adjuvant., (Copyright © 2018 Elsevier B.V. All rights reserved.)