Screening and Identification of Broad-spectrum Antibiotic-producing Strain GX-21
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Abstract:
A total of 1026 strains of actinomycetes were isolated from 156 soil samples collected from 11 locations in Guangdong Province and its surrounding areas. Soil was pretreated using enrichment culture method with calcium carbonate, and actinomycetes were isolated by plate dilution method. Gause No. 1 synthetic medium was used as the separation medium with 50 mg/L potassium dichromate as the inhibitor. Preliminary antibacterial screening using agar plug method, with five kinds of indicative bacteria including Staphylococcus aureus, Bacillus subtilis, Escherichia coli, Candida albicans, and Aspergillus niger, and 95 active strains were identified. Re-screening consisted of two screening levels with eight kinds of indicative bacteria, including the five used in preliminary screening and Vibrio parahaemolyticus, Pseudomonas aeruginosa, and Proteus vulgaris. The agar plug method used in the first level provided 19 active strains, and the Oxford cup diffusion method in the second level finally provided eight optimal strains. The optimal strain GX-21 was identified as Streptomyces polychromogenes based on morphological and cultural characteristics, physiological and biochemical tests, and 16S rDNA sequence analysis. This strain showed broad-spectrum antimicrobial activity, effective against gram-positive and -negative bacteria and fungi.
