Abstract
Optimization of agar column diffusion method was investigated to determine the antibiotic activity of Japanese radish.
1) Anaerobic growth of the seed bacterium (E. coli) in the agar column was disturbed by nitrate respiration with potassium nitrate in the radish. This respiration was effectively prevented by addition of 0.01% sodium azide to the culture medium.
2) Favourable concentration of agar in the medium was 0.8% for obtaining the clear boundary of the growth inhibition zone.
3) Addition of 0.1% Noigen P (polyethylenglycol laurylether) to the culture medium promoted the diffusion of slightly soluble antibiotic.
4) The composition of improved culture medium was as follows : polypeptone 0.5%, beef extract 0.3%, 0.5% methylenblue 0.01 (v/v), agar 0.8%, sodium azide 0.01% and Noigen P 0.1%. Sodium azide and Noigen P were added together with the seed bacterium after the other constituents were dissolved by heating and cooled at 45°C.
