Studies on the Susceptibility of Inbred Strains of Mice to Experimental Infection with Bacillus anthracis

Abstract

Mouse is in use as a laboratory animal for the safety test of anthrax vaccine No. 2. The results obtained in mice were frequently irregular as many experiments in spite of using a definite experimental method. The safety test, however, is closely associated with the security and the immunizability of the vaccine, so that constant result must be required. For that, a committee was formed among the persons concerned with the investigation of anthrax in Japan. The authors, as members of the committee, began to study on the part of mouse as a laboratory animal.
Three strains of mice, C3H, CF#1, and ddD, were subcutaneously and intravenously inoculated with Bacillus anthracis No. 2, strains 34F2 and H13. C3H was not susceptible and the LD₅₀ was 100 times as much as those of the other two. CF#1 was susceptible and the results were rather stable in mortality rate and survival times (Fig. 1 and 2) . Consequently, the strain CF#1 may be efficient for the safety test of vaccine No. 2.
The typical symptom of mice subcutaneously inoculated with the organisms is a hypodermal oedema formation. Then, it was presumed that a different attitude of oedema formation could be observed between C3H and CF#1. From the results of an experiment (Table 5), the hypodermal oedema formation was more difficult in C3H than in CF1. It was appeared that the difference of oedema formation between C3H and CF#1 is parallel to that of the susceptibility of both strains.
It is well known that a substance killing the organisms, anthracocidin, exists in human and rabbit sera and not in murine serum. Since the strain C3H was not susceptible, it was also presumed that an anthracocidin-like substance may exist in the serum of C3H. However, there was no evidence that the substance exists in the serum and in the saline extract of liver and spleen of C3H (Fig. 4) .