Nippon Saikingaku Zasshi

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During the past several years various mutants had been isolated from the same original strain of Staphylococcus aureus No.248 in the author's laboratory. They had been compared with one another in virulence in order to elucidate which one or which combination of the various genetic characters of this organism would play the most important role in the staphylococcal infection of man or animals.
In this paper are presented the results of experiments in which the virulence was compared between two mutants, 248αH and 248βH, especially in the case of intraperitoneal infection of mice. The former mutant produced α toxin but not β hemolysin. The latter strain produced β hemolysin but not α toxin. Both strains were identical in the other characteristics, including the abilities to produce coagulase, fibrinolysin, and DNase and to attack mannitol, as well as the phage type.
The results obtained are summarized as follows.
1. When injected intraperitoneally, these two strains showed a remarkable difference in virulence. No significant difference, however, was observed upon mice intravenously infected, except that the survival period was shorter in the αH-infected than in the βH-infected. The LD50 of the αH strain was estimated at about 0.6mg per mouse, and that of the βH strain at about 6mg, which was about ten times as large as the former.
2. The mice infected with the αH strain died earlier than those infected with the βH strain. When death occurred, it was usually encountered within one day in the former, but after two or three days in the latter.
3. This difference in virulence observed upon the intraperitoneal (i.p.) infection between the 248αH and 248βH strains is presumed to depend on the presence of α toxin. Strain 248Nβ produces neither α toxin nor β hemolysin. This strain is a mutant isolated from the 248βH strain. It shows a strong virulence upon the intravenous infection, but an extremely weak virulence upon the i.p. infection, just as the parent strain does.
4. When gastric mucin was added to the inoculum at 5%, such difference in virulence disappeared. Both strains similarly increased in virulence to such extent as to show an LD₅₀ of about 0.01mg per mouse.
5. In the i.p. infection, the distribution of organisms of both strains in various organs were examined for subsequent fate. The results indicated that organisms of the αH strain were much more invasive than those of the βH strain and could multiply in the peritoneal cavity to such extent as to produce an amount of α toxin large enough to kill mice.

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