A type III protein secretion system encoded by Salmonella pathogenicity isl
and 2 (SPI2) has been found to be required for virulence and survival withi
n macrophages. Here, SPI2 was shown to allow Salmonella typhimurium to avoi
d NADPH oxidase-dependent killing by macrophages. The ability of SPI2-mutan
t bacteria to survive in macrophages and to cause Lethal infection in mice
was restored by abrogation of the NADPH oxidase-dependent respiratory burst
. Ultrastructural and immunofluorescence microscopy demonstrated efficient
Localization of the NADPH oxidase in the proximity of vacuoles containing S
PI2-mutant but not wild-type bacteria, suggesting that SPI2 interferes with
trafficking of oxidase-containing vesicles to the phagosome.