Anaerobically induced Salmonella typhi genes are involved in entry and proliferation within human-derived cell lines.

Contreras, I., Obreque, V.H., Blanco, L.P., Toro, C.S. and Mora, G.C.

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Gene expression in response to oxygen availability has been examined in Salmonella typhi Ty2 by constructing mini-Mud (lac Kan) operon fusions. Among 12346 KanR insertion mutants we selected 25 clones which were induced when bacteria were grown under anaerobic conditions. We have characterized the phenotypes of the anaerobically induced mutants as well as their ability to enter into and proliferate within to human-derived cells lines: HEp-2 (epithelial) and U937 (monocytic-macrophages). Eighteen anaerobically induced operon fusion mutants presented a reduced capacity to invade at least one type of cells, and some mutants failed to enter both. Another mutants which invaded the cells normally was unable to proliferate either cell type. It was observed that an intact LPS is needed for S. typhi to enter to (or be phagocytosed by) U937 macrophages. In contrast, rough mutants invaded HEp-2 monolayers normally. All mutants were motile, although some of the rough mutants also presented a diminished motility. The parental strain grown under anaerobic conditions before incubation with HEp-2 or U937 cells, exhibited a higher capacity of invasion than aerobically grown bacteria. Our results suggest that certain genes induced under anaerobiosis are critical for S. typhi invasiveness, and very likely play a role during infection in humans.

Southeast Asian Journal of Tropical Medicine and Public Health 26. suppl 2:100-117 (1995).