Uropathogenic Escherichia coli Suppresses the Host Inflammatory Response via Pathogenicity Island Genes sisA and sisB

Abstract

ABSTRACT Extraintestinal pathogenic Escherichia coli can successfully colonize the urinary tract of the immunocompetent host. In part, this is accomplished by dampening the host immune response. Indeed, the sisA and sisB genes ( shiA -like i nflammation s uppressor genes A and B ) of uropathogenic E. coli strain CFT073, homologs of the Shigella flexneri SHI-2 pathogenicity island gene shiA , suppress the host inflammatory response. A double deletion mutant (Δ sisA Δ sisB ) resulted in a hyperinflammatory phenotype in an experimental model of ascending urinary tract infection. The Δ sisA Δ sisB mutant not only caused significantly more inflammatory foci in the kidneys of CBA/J mice ( P = 0.0399), but these lesions were also histologically more severe ( P = 0.0477) than lesions observed in mice infected with wild-type CFT073. This hyperinflammatory phenotype could be suppressed to wild-type levels by in vivo complementation of the Δ sisA Δ sisB mutant with either the sisA or sisB gene in trans . The Δ sisA Δ sisB mutant was outcompeted by wild-type CFT073 during cochallenge infection in the bladder ( P = 0.0295) at 48 h postinoculation (hpi). However, during cochallenge infections, we reasoned that wild-type CFT073 could partially complement the Δ sisA Δ sisB mutant. Consistent with this, the most significant colonization defect of the Δ sisA Δ sisB mutant in vivo was observed during independent challenge relative to wild-type CFT073, with attenuation of the mutant observed in the bladder ( P < 0.0001) and kidneys ( P = 0.0003) at 6 hpi. By 24 and 48 hpi, the Δ sisA Δ sisB mutant was no longer significantly attenuated in the bladder or kidneys, suggesting that the sisA and sisB genes may be important for suppressing the host immune response during the initial stages of infection.