THE VIRULENCE AND IMMUNOGENICITY OF SALMONELLA TYPHOSA GROWN IN CONTINUOUS CULTURE

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Abstract
The effect of continuous cultivation on the mouse virulence and immunogenicity of strains of Salmonella typhosa was studied. Two strains were employed. Strain Ty2 was continuously cultured for 24 days in a medium deficient in N with no discernible loss in mouse virulence. Dehydrated vaccines prepared from the cultures taken early in the experiment and on the 24th day were of comparable immunogenicity for mice, and both experimental vaccines were of the same order of potency as a standard preparation. However, a measurable change in the culture was observed after the 15th day of continuous growth since organisms previously able to resist agglutination by typhoid O antiserum became O-agglutinable. When strain Ty2 was cultured continuously in a medium deficient in glucose, the cells became O-agglutinable by the 8th day. At this time no loss in mouse virulence or immunogenicity was noted. The 2nd culture, strain V58, was grown continuously for 7 days. A heat-killed phenol -preserved vaccine was prepared from organisms on the 7th day. This preparation proved to be equal or possibly superior to a standard heat-killed vaccine in mouse protective potency.