Salmonella typhi rpoS mutant is less cytotoxic than the parent strain but survives inside resting THP-1 macrophages.

Transcription of the stationary-phase sigma factor RpoS of Salmonella typhi increased in the macrophage. A single rpoS mutant of S. typhi was constructed to analyze the role of RpoS in intracellular multiplication of the bacterium and host cell killing. This mutant was sensitive to starvation, low pH and hydrogen peroxide; however, it could still multiply inside resting macrophages and was less cytotoxic than the wild-type strain. Therefore, S. typhi might produce RpoS-dependent factors which could contribute to host cell death.