Host Restriction ofSalmonella entericaSerotype Typhi Is Not Caused by Functional Alteration of SipA, SopB, or SopD

Abstract

Salmonella enterica serotype Typhi is a strictly human adapted pathogen that does not cause disease in nonprimate vertebrate hosts, while Salmonella enterica serotype Typhimurium is a broad-host-range pathogen. Serotype Typhi lacks some of the proteins (effectors) exported by the invasion-associated type III secretion system that are required by serotype Typhimurium for eliciting fluid secretion and inflammation in bovine ligated ileal loops. We investigated whether the remaining serotype Typhi effectors implicated in enteropathogenicity (SipA, SopB, and SopD) are functionally exchangeable with their serotype Typhimurium homologues. Serotype Typhi elicited fluid accumulation in bovine ligated ileal loops at levels similar to those elicited by a noninvasive serotype Typhimurium strain (the sipA sopABDE2 mutant) or by sterile culture medium. However, introduction of the cloned serotype Typhi sipA, sopB, and sopD genes complemented the ability of a serotype Typhimurium sipA sopABDE2 mutant to elicit fluid secretion in bovine ligated ileal loops. Introduction of the cloned serotype Typhi sipA, sopB, and sopD genes increased the invasiveness of a serotype Typhimurium sipA sopABDE2 mutant for human colon carcinoma epithelial (HT-29 and T84) cells and bovine kidney (MDBK) cells. Translational fusions between the mature TEM-1 ␤-lactamase reporter and SipA or SopD demonstrated that serotype Typhi translocates these effectors into host cells. We conclude that the inability of serotype Typhi to cause fluid accumulation in bovine ligated ileal loops is not caused by a functional alteration of its SipA, SopB, and SopD effector proteins with respect to their serotype Typhimurium homologues.

Injection of Flagellin into the Host Cell Cytosol by Salmonella enterica Serotype Typhimurium

“…Plasmids pFlagTEM-1, pSipA/FT, and pGST/FT (where FT indicates FlagTEM-1 fusions) have been described previously (21). In plasmid pFlagTEM-1, the N-terminal signal sequence directing ␤-lactamase to the periplasm has been removed and replaced with a 3ϫFLAG epitope.…”

“…A fliC::Tn10 fljB::MudJ mutant (EHW26) was obtained from the Bäumler laboratory (26). For macrophage infection, S. Typhimurium was grown in Luria-Bertani (LB) broth to late logarithmic phase to maximize expression of the Salmonella pathogenicity island 1-encoded Type III secretion system (T3SS-1), as described previously (21).…”

“…Although injection of effector proteins into host cells by the S. Typhimurium SPI-1 T3SS has been visualized microscopically (21,22), it has not yet been demonstrated that in infected cells, bacteria are able to translocate flagellin from a membrane-bound compartment into the cytosol. In this report, we show that S. Typhimurium translocates flagellin into the cytosol of infected cells by a process that depends on the SPI-1 T3SS but is independent of the flagellar T3SS.…”

Molecular insights into farm animal and zoonoticSalmonellainfections

“…For example, SopA is truncated in the sequenced genomes of serovars Gallinarum (Thomson et al 2008) and Choleraesuis (Chiu et al 2005). SopA and SopE2 are absent in serovar Typhi, but the remaining enteritis-associated effectors SipA, SopB, and SopD remain active and, when exchanged for their cognate effectors, do not transfer an altered phenotype to S. Typhimurium in bovine ileal loops (Raffatellu et al 2005). Owing to the potential for effectors to subvert cellular processes in cell-, tissueand host-specific ways, activities detected in one system may not be relevant in others.…”

Impact ofSalmonella entericaType III Secretion System Effectors on the Eukaryotic Host Cell

“…Salmonella invasion protein A (SipA) is a protein encoded on SPI1 [220] that is delivered into the host cell through T3SS1 [21]. This effector has a role in invasion of epithelial cells by modulating actin assembly through its Cterminal actin-binding domain, stabilizing F-actin filaments, and increasing the bundling activity of the host protein Tplastin [21,[221][222][223]. SipA contributes, together with other T3SS1 effectors, to the disruption of tight junctions, protein complexes intimately linked to the actin cytoskeleton that are located at the interface between epithelial cells [38].…”