Differences in Susceptibility of Inbred Mice to Bacillus anthracis
ARMY MEDICAL RESEARCH INST OF INFECTIOUS DISEASES FORT DETRICK MD
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Animal species differ in their resistance both to infection by B. anthracis and to anthrax toxin. A mouse model was developed to study the basis of these host differences and the pathogenesis of infection. When infected with the virulent B. anthracis strain Volume 1B, all eight strains of inbred mice tested had low LD50 values 5 to 30 spores. However, analysis of time-to-death TTD data revealed significant differences between the strains, which could be divided into three groups most susceptible AJ, DBA2J, and C3HHeN intermediate C57BL6J, C57LJ, and C58J and least susceptible CBAJ and C57BRcdJ. In contrast, the mice were distinctly susceptible or resistant to lethal infection by Sterne vaccine strain. The LD50 of the susceptible AJ and DBA2J mice was approximately 1,000 Sterne spores whereas the remaining six relatively resistant strains were killed only by 0.2 to 2 x 10,000,000 spores. Mice lethally infected with B. anthracis had an acute course, characterized by extensive gelatinous edema and large concentrations of bacilli in the blood and organs e.g. 1,000,000,000 CFUg spleen. To study susceptibility to anthrax toxin, the protective antigen PA and lethal factor LF components of the toxin were injected i.v. into AJ and CBAJ mice. As reported earlier for various animal species, susceptibilities of the mice to anthrax toxin appeared to be independent of that to infection. The toxin LD50 values for both strains were about 12 micrograms PA combined with 2.4 micrograms LF.
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