The use of inactive dried yeast instead of mucin as a pathogenicity promoting substance in the typhoid mouse protection test

Abstract

A 5% suspension of ‘Saccharomyces cerevisiae siccum’ (dried inactive baker's yeast) can be used equally well in the typhoid mouse protection test as 5% mucin. The yeast suspension, however, is much less viscous and therefore easier to use. The yeast suspension appears to have about the same pathogenicity promoting activity weight for weight for typhoid as does mucin. With both substances the LD 50 of the challenge culture is about 1–5 germs. The slopes of probit lines in mouse protection tests are equal in both cases. The same holds true for phenol- and acetone-inactivated vaccines. A relation between the anticomplementary effects and the virulence promoting activity of mucin and yeast could not be demonstrated.