Jean-Mathieu Leclerc, Eve-Lyne Quevillon, Yoan Houde, Kiran Paranjape, Charles M. Dozois, France Daigle
The Typhi colonization factor (Tcf) is one of the twelve putative chaperone/usher fimbrial clusters present in the Salmonella enterica serovar Typhi (S. Typhi) genome. We investigated the production, expression and regulation of tcf as well as its role during interaction with human cells. The tcf gene cluster was cloned and induced in E. coli and S. Typhi and the production of intertwined fibers similar to the cable pili of Burkholderia cepacia, were observed on the bacterial surface by electron microscopy. In S. Typhi, tcf was more expressed after growth in M63 minimal medium than in standard LB medium. Analysis of the promoter region identified putative binding sites for the global regulators RcsB, ArgR and Fur. The expression of tcf was measured in isogenic strains lacking these global regulators. Under the conditions tested, the results showed that tcf expression was higher in the fur mutant and was regulated by iron concentration. Fur may regulate this fimbria indirectly via the small RNAs RyhB1 and RyhB2. An isogenic mutant harbouring a deletion of the tcf cluster did not demonstrate any defect in adhesion or invasion of human epithelial cells, or in phagocytosis or survival in macrophages, when compared to the wild-type serovar Typhi strain. However, the tcf cluster contributed to adherence to human epithelial cells when introduced into E. coli. Thus, tcf genes encode functional fimbriae that can act as an adhesin and may contribute to colonization during typhoid fever.
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