Of Invaders and Islets

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Science  06 Apr 2001:
Vol. 292, Issue 5514, pp. 17
DOI: 10.1126/science.292.5514.17c

Salmonella bacteria enter cells lining the gut and survive within a membrane-bounded vacuole. Normally, organisms that invade cells are attacked by host lysosomes (which contain degradative enzymes), but Salmonella manages to thwart attack by preventing its vacuole from fusing with a lysosome. A few hours after entry, the Salmonella-containing vacuole forms an extensive network of tubular filaments, possibly for nutrient uptake, but no one knows how this happens.

Salmonella typhimurium has two syringe-like delivery systems, which it uses to inject virulence determinants into the host cell. These are encoded by two major gene clusters called pathogenicity islands and by other minor regions or islets. Brumell et al. show that a protein called SifA, which is key to the formation of the tubular filaments, is one of the virulence determinants injected by the bacterium. Although its mode of action remains unknown, SifA is essential for the survival of Salmonella during systemic infection when it colonizes host macrophages that normally are aggressively protective. SifA appears to be one of a family of proteins encoded by pathogenicity islets, sharing conserved motifs required for injection into the host cell, and that operate in concert to modulate host-cell function. — CA

Cell. Microbiol.3, 75 (2001).

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