抄録
A mutant (mucoid var. of Mutabile-type var. Murase) was found in author's laboratory which has two kinds of weak characters, one being galactose-sensitivity and the other mucoid growth. Even if one of them might be lost by mutation, the other character would still remain.
A study of weak live vaccine was undertaken utilizing such a peculiar mutant of. Salmonella and the antibacterial activity of the host to the mutant.
Following points were cleared.
1) Mucoid M of S. enteritidis and S. typhimurium are found weakly virulent mutants for mouse, retaining the antigenicity as M. Mice immunized with the mutant resist to the challenge of wild virulent type.
2) Mice sometimes die from the sepsis of RT, the backmutant to the wild type, by inoculation of mucoid M.
3) Mucoid RT is less virulent than the original.
4) Mice sometimes die from the sepsis of RT by inoculation of mucoid RT more often than mucoid M.
The directions of mutation is such as mucoid M→M→RT when the mucoid character is lost, and mucoid M→mucoid RT→RT when the M character is lost.
If both characters could be lost at the same time, mucoid M→RT should follow. But this kind of mutation is rarely experienced in vitro test.
From the above experiment, it was cleared that the backmutation of mucoid M to the original may occur at a certain ratio in various ways in vitro as well as in vivo. So it is hoped to obtain a mutant with the mutation rate as low as posssble, rich in antigenicity, and stable in these characters. In author's experiments, both mutation rates of mucoid M to mucoid RT and mucoid M to M are roughly estimated as 104to 1, and thus the death of animal occured by thee backmutant. This observation, however, may introduce a new conception for the vaccine prophylaxis of typhoid fever.
