Studies on Immunization Against Plague. V. Multiplication and Persistence of Virulent and Avirulent Pasteurella Pestis in Mice and Guinea Pigs

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Abstract
Summary: Some avirulent strains of Pasteurella pestis progressively decrease in numbers in host tissue without indication of multiplication, but viable bacilli can still be found up to the 6th to the 9th days after inoculation. Other strains maintain their numbers well for 5 or 6 days and are then progressively eliminated. Some strains multiply and definitely increase in numbers before being overcome and the tissue sterilized. With the avirulent strains studied, at no time were bacilli cultured from the blood later than 15 minutes after injection. Those strains which are effective in stimulating development of immunity in mice may be the ones that, even though incapable of extensive multiplication, are rich in soluble envelope antigen or may be the ones that, although less productive of envelope antigen, have the capacity to multiply and to attain numbers adequate to provide necessary quantities of envelope antigen.