Role of Flagella in Pathogenesis ofPseudomonas aeruginosaPulmonary Infection

Abstract

Pseudomonas aeruginosa strains are opportunistic pathogens associated with infections in immunocompromised hosts and patients with cystic fibrosis. Like many other mucosal pathogens,P. aeruginosa cells express flagella which provide motility and chemotaxis toward preferred substrates but also provide a ligand for clearance by phagocytic cells. We tested the role of flagella in the initial stages of respiratory tract infection by comparing the virulence of fliC mutants in a neonatal mouse model of pneumonia. In the absence of fliC, there was no mortality, compared with 30% mortality attributed to the parental strain PAK or 15% mortality associated with infection due to a pilAmutant PAK/NP (P < 0.0001). The fliCmutants caused pneumonia in only 25% of the mice inoculated, regardless of whether there was expression of the pilus, whereas the parental strain was associated with an 80% rate of pneumonia. Histopathological studies demonstrated that the fliCmutants caused very focal inflammation and that the organisms did not spread through the lungs as seen in infection due to either PAK or PAK/NP. Purified flagellin elicited an intense inflammatory response in the mouse lung. 125I-labeled flagellin bound to the glycolipids GM1 and GD1a and to asialoGM1 in an in vitro binding assay. However, flagellin-mediated binding to epithelial gangliosides was a relatively unusual event, as quantified by binding assays of wild-type or fliC mutant organisms to CHO Lec-2 cells with membrane-incorporated GM1. Fla+ organisms but not fliC mutants were efficiently taken up by murine macrophages. P. aeruginosa flagella are important in the establishment of respiratory tract infection and may act as a tether in initial interactions with epithelial membranes. This function is offset by the contribution of flagella to host clearance mechanisms facilitating phagocytic clearance and the role of flagellar genes in mucin binding and clearance.

Role of Shiga toxin versus H7 flagellin in enterohaemorrhagic Escherichia coli signalling of human colon epithelium in vivo

“…This suggested Caco-2 cells as a suitable in vitro model for studying flagellin signalling. Using that model, flagellin signalling was shown to be mediated strictly through TLR5, and not an alternate receptor such as the ganglioside asialoGM1, which had been reported by others to function as a alternative receptor for bacterial flagellin on airway epithelial cell lines (DiMango et al, 1995;Feldman et al, 1998;Adamo et al, 2003;Ogushi et al, 2004;West et al, 2005). Studies in this model further showed that EHEC flagellin was both necessary and sufficient for upregulating CXCL8 in the context of EHEC infection.…”

“…Flagellin from Pseudomonas aeruginosa was reported to activate NF-κB production in airway epithelial cells by signalling through either TLR5 or the ganglioside asialoGM1 (DiMango et al, 1995;Feldman et al, 1998;Adamo et al, 2003), raising the possibility that flagellin induction of the NF-κB target gene CXCL8 in colon cancer cell lines might take place through an alternative receptor. However, this was not the case.…”

An investigation of the expression and adhesin function of H7 flagella in the interaction ofEscherichia coliO157 : H7 with bovine intestinal epithelium

“…We propose that TLR5 is unlikely to be the initial receptor for flagella as the flagellin domain that binds TLR5 forms part of the core of the flagellar filament (Eaves-Pyles et al, 2001;Smith et al, 2003), and thus is not exposed in the native structure and TLR5 is usually located on the basolateral surface of enterocytes (Gewirtz et al, 2001). Other epithelial receptors or coreceptors for flagella have been proposed, including TLR2 (Adamo et al, 2004), gangliosides (Feldman et al, 1998;McNamara et al, 2001;Ogushi et al, 2004) and mucin (Lillehoj et al, 2002). Recently it has been shown that H7 flagella bind mucus potentially via Muc2 (Erdem et al, 2007b).…”

Calcium signalling during cell interactions with bacterial pathogens

“…Whether these Ca 2+ responses involve binding of flagellin to TLR(toll-like receptor)-5, a receptor belonging to the TLR family of pattern-recognition molecules crucial for innate immunity (Fearon and Locksley, 1996;Zhang and Ghosh, 2001), and that was described to act as receptor for bacterial flagellin (Takeda et Akira, 2001), is unclear. In the case of P. aeruginosa, the flagellin was also shown to bind to asialoGM1 (ASGM1), a glycolipid receptor (Feldman et al, 1998;Mc-Namara et al, 2001;Fig. 2).…”