FIG. 3.

Long-term intracellular survival and growth is not required for delayed macrophage killing. (A) J774 macrophages were infected with stationary-phase cultures (conditions shown to turn off SPI1-dependent rapid induction of macrophage cell death) of either wild-type serotype Typhimurium, a spiB mutant strain, or a macrophage-sensitive prc-deficient strain, after which macrophage survival was determined at 15 and 18 h postinfection (three times each) by measuring the viable intracellular CFU. (B) Macrophage cytotoxicity was quantitated at these times by measuring the release of cytoplasmic LDH. The data are arithmetic means of at least three independent experiments from 15-h time points. The error bars indicate the standard deviations of the mean.