Assay of some antifungal antibiotics using Piricularia oryzae as the test organism.

Abstract

(1) Piricularia oryze was used as the most senstive test organism of microassaying some antifungal antibiotics by the cup or the paper disc method. Spores of P. oryzae were obtained by cultivating the organism on the yeast starch agar slants at 28°C for 2 weeks. The concentration of spores in the assay medium necessary for optimum results was about 17 -34×10⁴ spores per ml (Fig. 3).
(2) A Study was made on the factors affecting the Blasticidin assay. The most important factors to be controlled in the assay of Blasticidin were hydrogen ion concentrations of the assay medium . and of the sample solutions. As shown in Fig. 1 and 2, Blasticidin gave the highest activity against P. oryzae at pH 5.0 in both of them.
(3) The cup method for assaying Blasticidin was established. The assay medium was as follows: Soluble starch 10g, yeast extract 1g, agar 15g and 0.1M PO₄ buffer of pH 5.0 1, 000 ml. The sample solutions were made with 0.1 M PO₄ buffer of pH 5.0. As shown in Fig 4, the excellence of log dose-response curve and its linearity within the range of 0.2-2.0mcg/ml warrants the use of the cup method.
(4) The paper disc method was adapted to the assay of Antimycin A and Blastmycin. The assay media were made with distilled water. Samples were dissolved in methanol The linear relations were found between the diameters of inhibition zones and the log concentrations within the ranges of 0.05-5.0mcg/ml of Antimycin A and 0.05-0.5mcg/ml of Blastmycin. The potency are calculated on the basis of this relation.