Isolation and Identification of a bacterium producing antimicrobial component from frog skin (Bufo), evaluation of antimicrobial component effects and its extraction

Background and objectives: Researches linked to investigate new antimicrobial agents that are produced in natural way have great significance to achieve new pharmaceutics resources. The present study is aimed to identify a new and effective antimicrobial agent from an isolated antibiotic producing bacterium from frog skin. Material and method: The bacteria were isolated by serial dilution method on nutrient agar according to their morphologies. Identification of bacterium was performed by molecular method and standard biochemical tests. Process optimization of antimicrobial component production was studied based on sources of carbon, optimum temperature and pH that experiments carried out in fed batch system. The supernatant was concentrated on the disk and then tested on several standard strains including Bacillus subtilis, Candida albicans, Aspergillus niger and Escherichia coli. Extraction of the antimicrobial component was done by chloroform and ethyl acetate as organic solvents and then antimicrobial test was done by both organic and watery phases. Results: This isolated bacterium was a gram positive, rod shape, aerobic, oxidase and catalase-positive strain producing yellow pigment. Glycerol and glucose possessed the most positive effect on antimicrobial component biosynthesis. Results of disk diffusion showed that antimicrobial component production is maximum in pH of 7.0 and at 25◦ C. The antimicrobial component was polar and its effect spectrum against gram negative bacteria was more than that of gram positive bacteria. Conclusion: The results revealed that the isolated bacterium had an affinity with Bacillus pumilus. Given the possibility that the isolated bacterium from frog skin might be a new strain with respect to variety of climates in Iran, more studies are encouraged on different species of frogs living in different types in this country.