カップ法によるビタミンB群の微生物定量にかんする基礎的研究 : (VII)Streptococcus faecalisを用いるカップ法による葉酸定量条件の検討

抄録

In a previous paper, it was suggested that a cup-plate method with Streptococcus faecalis as test organism might be available for the microbiological assay of folic acid, and on that occasion the folic acid content of powdered agar added to assay medium affected the sharpness of the zones of exhibition. Thus, a favourable condition was reexamined for obtaining the growth zones of the best character using the agar from which extracted the vitamin as much as possible, and the precision of the assay method was further analysed. The following condition was required for the present purpose. Assay medium : AOAC's composition with 1% purified agar, 1.5 mm plate thickness, pH 6.8 to 7.5. Folic acid solution : pH 7.0 to 7.5. Inoculum density of test organism : 0.025 OD in final. Incubation : 37℃, 16 to 18 hrs. Under the condition there was a linearity of the dose response to the standard solution of folic acid over a wide range of 100 to 4,000 mμg per ml, and in the statistical evaluation of the results the maximum errors of the estimate were below 10%. The precision of the plate assay method could be improved by the use of purified agar and the establishment of optimal condition for folic acid determination.