||Identification of a pil operon in serovar Typhi suggested that this serovar strain might synthesize Type IV pili (Zhang et al., 1997). Under the normal growth conditions used, expression of the Type IVB pili by serovar Typhi J341 appeared to be weak (Zhang et al., 2000). It thus seemed unlikely that it would be possible to purify PilS protein from serovar Typhi. To allow protein purification, a gene fusion, which would encode the fusion protein with PilS attached to a His-tag, was prepared, and the tagged protein was purified by affinity methodology. The expression vector was successful to over-express the 6xHis tagged-PilS fusion protein at a high level. Next, the effect on pilS gene expression of exposure of serovar Typhi to solutions containing bile salts was investigated. Bile salst are naturally found in the human intestine, and it was thought that such materials might modulate expression of the Type IVB pili demonstrated that low concentrations of bile salts appeared to inhibit pilS gene expression, which was, however, surprisingly unaffected by higher concentrations of these natural emulsifiers.