The fate of hemolytic staphylococci injected intravenousiy into albino mice was followed by determining quantitatively the numbers of living organisms present in the various tissues at different intervals of time after infection.

Irrespective of the strain of staphylococcus used, most of the organisms disappeared rapidly from the blood, liver, spleen, and kidneys. This was true even when the infective dose consisted of large numbers of virulent, coagulase-positive staphylococci, capable of producing a fatal disease in a high percentage of the infected mice. The initial rate of removal or destruction of staphylococci was particularly high in the lungs and kidneys. In all cases on the other hand, a few living staphylococci persisted in the various organs for several weeks after infection, even when the organisms were non-virulent and coagulase-negative.

Although virulent as well as avirulent staphylococci were eliminated extremely rapidly and efficiently from the kidneys during the initial stage of infection, the microorganisms soon began to multiply in this organ, causing abscesses first detected in the cortex. Death of the animals infected with virulent cultures appeared to be due to the destruction of renal tissue by these abscesses. The abscesses caused by the avirulent strains eventually became sterile, and healed.

No convincing difference could be recognized amongst seven strains in their resistance to the bactericidal power of the mouse tissues during the initial phase of the infection. In contrast, marked quantitative differences came to light in their subsequent behavior in the kidneys. The multiplication of the coagulase-negative staphylococci in this organ soon came to an end in all animals and never proceeded far enough to result in fatal disease. The staphylococci of a weakly coagulase-positive strain multiplied somewhat more extensively in the kidneys than did the coagulase-negative, but never sufficiently to cause the death of any animal within the period of observation of 1 month. The three coagulase-positive strains tested yielded the largest bacterial population in the kidneys and caused the death of many of the infected animals. These three virulent strains differed quantitatively amongst themselves with regard to both the rapidity and extent of their multiplication in the kidneys and the lethal power of a given infective dose.

Taken together, the findings indicate that the hemolytic strains of staphylococci can be arranged in a continuous spectrum according to their ability to cause disease in albino mice. Although virulence for these animals appeared to be correlated with the production of coagulase, it did not seem to depend upon the ability of this substance to interfere with the bactericidal mechanisms of the mouse organs during the early phase of the infection. Virulence manifested itself chiefly by the production in the kidneys of progressive abscesses originating from the few staphylococci which were not destroyed during the initial bactericidal reaction.

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