The fate of temperature-sensitive salmonella mutants in vivo in naturally resistant and susceptible mice.

The in vivo net growth rate of salmonellae in mice is faster with virulent than with attenuated strains, and slower in resistant than in susceptible mice, the latter difference being controlled by a single host gene (Ity). Mice were injected intravenously (i.v.) with nonreplicating temperature-sensitive (TS) salmonellae mutants: TS mutants from virulent parents survived better in the RES than those from attenuated or non-virulent parents as if the latter were more susceptible to bactericidal mechanisms. However, a TS mutant from a virulent parent (Salmonella typhimurium C5) did not consistently survive better in susceptible C5) did not consistently survive better in susceptible Itys than in resistant Ityr mice, suggesting that this gene may not operate by a bactericidal mechanism. In many animals the TS salmonellae caused septic arthritis which first appeared at 2--3 weeks. Subcutaneous inoculation in the tail caused local lesions and the organism spread to the RES, but did not cause arthritis in the short term.