Contribution of the SitABCD, MntH, and FeoB Metal Transporters to the Virulence of Avian Pathogenic Escherichia coli O78 Strain χ7122

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Abstract
The roles of SitABCD, MntH, and FeoB metal transporters in the virulence of avian pathogenic Escherichia coli (APEC) O78 strain χ7122 were assessed using isogenic mutants in chicken infection models. In a single-strain infection model, compared to χ7122, the Δ sit strain demonstrated reduced colonization of the lungs, liver, and spleen. Complementation of the Δ sit strain restored virulence. In a coinfection model, compared to the virulent APEC strain, the Δ sit strain demonstrated mean 50-fold, 126-fold, and 25-fold decreases in colonization of the lungs, liver, and spleen, respectively. A Δ mntH Δ sit strain was further attenuated, demonstrating reduced persistence in blood and mean 1,400-fold, 954-fold, and 83-fold reduced colonization in the lungs, liver, and spleen, respectively. In coinfections, the Δ feoB Δ sit strain demonstrated reduced persistence in blood but increased colonization of the liver. The Δ mntH , Δ feoB , and Δ feoB Δ mntH strains were as virulent as the wild type in either of the infection models. Strains were also tested for sensitivity to oxidative stress-generating agents. The Δ mntH Δ sit strain was the most sensitive strain and was significantly more sensitive than the other strains to hydrogen peroxide, plumbagin, and paraquat. sit sequences were highly associated with APEC and human extraintestinal pathogenic E. coli compared to commensal isolates and diarrheagenic E. coli . Comparative genomic analyses also demonstrated that sit sequences are carried on conjugative plasmids or associated with phage elements and were likely acquired by distinct genetic events among pathogenic E. coli and Shigella sp. strains. Overall, the results demonstrate that SitABCD contributes to virulence and, together with MntH, to increased resistance to oxidative stress.

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