Characterization of the anaerobically induced outer membrane protein Tsx of Salmonella typhi Ty2 and its relation with Salmonella virulence

Bucarey, S., Bittner, M. and Mora, G. Laboratorio de Microbiología, Departamento de Genética Molecular y Microbiología, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile.

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Salmonella typhi, a Gram negative enterobacteria is the agent causing typhoid fever only in humans. The systemic infection begins when this pathogen invades the intestinal epithelium. An important environmental condition of the intestine (ileum)is the low oxygen availability and it is known that this condition enhances the invasive ability of S. typhi. However, the genes responsible for this ability have not been caracterized. Our hypothesis is that "outer membrane proteins induced under anaerobic conditions play a role in the S. typhi invasivity". In this work we have analyzed the most strongly anaerobicaly induced outer membrane proteins of the typhoid bacillus. One of these proteins was purified by uni- and bidimensional gel electroforesis and its N-terminal region sequenced. This protein was identified as porin Tsx, which has been sugested to be specific pore for nucleosides in E. coli. To evaluate the role of this porin in the capability of Salmonella to invade and proliferate, we mutagenized de tsx gene by insertion of a suicide vector (pGP704) containing an inner fragment of the gene. The invasion and proliferation capability of the mutant was evaluated by "in vitro" assays using cultured epithelial cells (HEp-2). Our result indicate that the mutant invasiveness decreases in 70% compared to the reference strain S. typhi Ty2. Furthermore, at the present time we have used the same strategy to mutagenize the tsx gene of the virulent Salmonella typhimurium, strain 14028. This mutant infectivity is been at present evaluated in mice.