Metabolic events mediating early killing of host cells infected by Shigella flexneri.

J774, a continuous macrophage cell-line, was infected by M90T, an invasive isolate of Shigella flexneri serotype 5 and BS176, its non invasive derivative--which does not harbor the 220 kbase virulence plasmid pWR100. Killing of host cells by intracellular M90T, commenced one hour after infection and was completed by 4 hours. Intracellular BS176 did not kill cells during the same period. Cell protein biosynthesis was totally inhibited by both strains within 2 hours of infection thus indicating that shiga-like toxin 1 (SLT1) could not account for early killing. On the other hand a sharp decrease in intracellular ATP was observed after 1 hour in cells infected with M90T. No significant increase in ATPase activity could be detected. A sharp increase in pyruvate production starting immediately after infection indicated impairement in mitochondrial respiration, which accounts for most ATP produced intracellularly. In addition, fermentation appeared to be totally blocked thus leaving no chance of the infected cells regenerating NAD. Concurrent increase in cAMP concentration within the first hour of infection may contribute to the rapid and efficient cell killing. Cells infected by BS176 always showed an intermediate phenotype (i.e. ATP depletion, pyruvate increase, lactate decrease). Early lysis of the phagocytic vacuole by M90T may account for this difference by allowing toxic products of the bacteria to diffuse more efficiently within the cytosol.