Pathogenic Bacteria, Candida albicans.

Soil actinomycetes are recognized as promising sources of new antimicrobials. Antimicrobial resistance in pathogens has greatly increased in recent years, and has become a global public health problem. New antimicrobials are continuously required to combat these resistant strains. The aim of this study was to isolate and screen soil actinomycetes and evaluate their secondary metabolites for antimicrobial activities against selected pathogenic bacteria and fungi. Four soil samples were collected, pre-treated with CaCO3, serially diluted and spread plated on actinomycetes isolation agar (AIA) and international streptomyces project media 2 (ISP-2), supplemented with nystatin, neomycin and polymyxin B . Perpendicular streak method was used to check antagonistic activities of the isolated actinomycetes against test microorganisms. Small scale submerged fermentation system was used for the production of antimicrobial metabolites from the isolates. Agar well diffusion was then used to evaluate antimicrobial activities of the crude extracts against the test microorganisms. The average aerobic actinomycetes plate count from the different soil samples ranged from 3.0×10 4 ± 2.4 to 3.6×10 4 ± 1.9 CFU/g. A total of 28 different microorganisms were isolated, characterized by cultural and morphological methods and identified as actinomycetes. Out of the 28 isolates, 10 (36%) showed antimicrobial activities on primary screening; from which isolates BYQ3, CYP1, CYP2, CYP4 and CYQ2 were selected for their wide spectrum of activities. Diameters of inhibition zones produced by these 5 isolates against the test microorganisms on secondary screening, ranged from 0 to 26 mm. Isolates CYP1 and CYP2 had the widest zones with CYP1 producing 26 mm against Candida albicans. The two promising isolates were further characterized by physiological and biochemical tests and identified as genus Streptomyces. Isolate CYP1 was then identified to the specie level by 16S rRNA gene sequence analysis which confirmed that Streptomyces sp. CYP1 was homologous to Streptomyces albus (strain DSM 40313) of the order Actinomycetales and class Actinobacteria. Optimization of production conditions, further purification, structural elucidation and characterization are recommended to know the quality, novelty and commercial value of these antimicrobials key words