Contribution of thestgFimbrial Operon ofSalmonella entericaSerovar Typhi during Interaction with Human Cells

Abstract

Salmonella serovars contain a wide variety of putative fimbrial systems that may contribute to colonization of specific niches. Salmonella enterica serovar Typhi is the etiologic agent of typhoid fever and is a pathogen specific to humans. In a previous study, we identified a gene, STY3920 (stgC), encoding the predicted usher of the stg fimbrial operon, that was expressed by serovar Typhi during infection of human macrophages. The stg genes are located in the glmS-pstS intergenic region in serovar Typhi and certain Escherichia coli strains, but they are absent in other S. enterica serovars. We cloned the stg fimbrial operon into a nonfimbriate E. coli K-12 strain and into S. enterica serovar Typhimurium. We demonstrated that the stg fimbrial operon contributed to increased adherence to human epithelial cells. Transcriptional fusion assays with serovar Typhi suggested that stg is preferentially expressed in minimal medium. Deletion of stg reduced adherence of serovar Typhi to epithelial cells. However, deletion of stg increased uptake of serovar Typhi by human macrophages, and overexpression of stg in serovar Typhi and serovar Typhimurium strains reduced phagocytosis by human macrophages. These strains survived inside macrophages as well as the wild-type parent. Although the stgC gene contains a premature stop codon that disrupts the expected open reading frame encoding the usher and is therefore considered a pseudogene, our results show that the stg operon may encode a functional fimbria. Thus, this serovar Typhi-specific fimbrial operon contributes to interactions with host cells, and further characterization is important for understanding the role of the stg fimbrial cluster in typhoid fever pathogenesis.

Ethanolamine and Choline Promote Expression of Putative and Characterized Fimbriae in Enterohemorrhagic Escherichia coli O157:H7

“…Previous work has demonstrated that the transport and assembly machineries of separate fimbriae are able to bind and protect the heterologous subunits and incorporate these subunits into functional hybrid fimbriae (38)(39)(40). Furthermore, the lpf1 (loc12) and elf (loc5) genes of EHEC as well as the stg fimbrial operon of Salmonella enterica contain premature stop codons; however, these fimbriae play a role in the adherence of these pathogens (25,(41)(42)(43)(44). Moreover, production of Lpf1 and Elf fimbriae on the outer surface of EHEC has been demonstrated (25,44).…”

Phase variation has a role in Burkholderia ambifaria niche adaptation

“…Macrophage infection assays were performed using the human acute monocytic leukemia cell line THP-1 as described in Forest et al (2007), with the following modifications: bacteria grown overnight at 37 1C in static conditions in TSB were added to a cell monolayer at a multiplicity of infection of 10. After incubation for 20 min at 37 1C (time 0), the infected cells were washed three times with prewarmed phosphate buffered saline.…”

Typhi genes expressed during infection or involved in pathogenesis

“…The pil genes encoding for type IV pili facilitate Typhi entry into human intestinal epithelial cells and macrophages [37,38]. The deletion of stg reduced adherence of Typhi to epithelial cells but increased uptake by human macrophages, although survival inside macrophages was similar to the wild-type parent [39] (Table 1).…”