Abstract
Reproducible and sharply defined growth zones of the test organism were obtained under the following conditions of assay procedure. Assay medium : Johansson's medium with 1% agar, thin agar plate (0.75mm plate thickness), pH 7.5 to 8.5. Cyanocobalamin solution : pH 7.0. Inoculum density of test organism : 0.025 OD in final. Incubation : 37℃, 16 to 18 hrs. Under the optimal condition there was a linearity of the dose response to the standard solution of the vitamin over a wide range of 1 to 100mμg/ml. The statistical analysis of the assay results showed that the maximum errors of the estimate using 5 plates were below 20%. A thin agar plate method with a variant of E.coli may be available for the microbiological determination of cobalamin, though the organism has a disadvantage of a relative response to a certain amino acid, e.g., methionine.
