Development of a Sensitive Microbioassay Using Amplified Cultivation

抄録

A novel ultramicro microbioassay was developed. The present method, referred to as amplified cultivation, is composed of two successive kinds of culture. The first culture is performed until a maximum difference is obtained in the ratio of numbers of viable cells appearing in a basal medium and that contained in a nutrient. The second culture is continued after adding a complete medium to the cultures and stopped just after the growth of microorganisms in the blank reaches a certain detectable limit, e. g., by optical density or acid production. Lactose was analyzed by this amplified cultivation method with an extremely low concentration of viable cells of Bifidobacteriumz bifidum N4 as the inoculum. The detectable limits of lactose were 0.05μg and 1μg by the test tube method and by the pulp disc method respectively, with an increase in sensitivity by a factor of more than 10³ compared with the corresponding conventional microbioassays. Moreover, a relationship between the diameters of the growth zones and the logarithm of the amount of lactose was achieved in a range of 50-1000μg of lactose in the pulp disc method.