Comparative studies onSalmonella typhigrownin vivoandin vitroI. Virulence, toxicity, production of infection-promoting substances and DPN-ase activity

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Abstract
1. The virulence ofS. typhistrains Ty 2 and O 901 injected intra-abdominally into white mice was examined. The lethal dose of strain Ty 2 grownin vivowas lower than that of the corresponding culture grownin vitro, while the lethal doses of thein vivo- andin vitro-grown strain O 901 were almost identical.2. The extracts of infected livers and spleens were not toxic, but acted as infection-promoting substances. Extracts from normal organs exerted similar but weaker effects. Glycogen together with sodium taurocholate were powerful infection-promoting substances. The highest increases of virulence were observed when spleen-grown bacteria together with extracts from infected organs were injected.3. Extracts from infected spleen, pancreas, stomach and lower intestines, spleen-grownS. typhi, other spleen-grown Enterobacteriaceae, and bacteria taken from the intestines of normal and diseased animals, exhibited high DPN-ase activity.4. The extracts from infected organs contained soluble bacterial antigens. Their presence was demonstrated by tube precipitation, agar gel precipitation and antibody production after immunization of rabbits with extracts from infected organs with addition of adjuvants.5. Spleen-grown bacteria were able to absorb host antigens and to produce, in addition to the known agglutinating antibodies, anti-spleen precipitins.