Roles of iron acquisition systems in virulence of extraintestinal pathogenic Escherichia coli: salmochelin and aerobactin contribute more to virulence than heme in a chicken infection model

Qingqing Gao,Xiaobo Wang,Xiufan Liu,Huiqing Xu,Debao Zhang,Song Gao,Yaya Xu,Jielu Ling

doi:10.1186/1471-2180-12-143

Abstract

BackgroundAvian pathogenic Escherichia coli (APEC) and uropathogenic E. coli (UPEC) are the two main subsets of extraintestinal pathogenic E. coli (ExPEC). Both types have multiple iron acquisition systems, including heme and siderophores. Although iron transport systems involved in the pathogenesis of APEC or UPEC have been documented individually in corresponding animal models, the contribution of these systems during simultaneous APEC and UPEC infection is not well described. To determine the contribution of each individual iron acquisition system to the virulence of APEC and UPEC, isogenic mutants affecting iron uptake in APEC E058 and UPEC U17 were constructed and compared in a chicken challenge model.ResultsSalmochelin-defective mutants E058ΔiroD and U17ΔiroD showed significantly decreased pathogenicity compared to the wild-type strains. Aerobactin defective mutants E058ΔiucD and U17ΔiucD demonstrated reduced colonization in several internal organs, whereas the heme defective mutants E058ΔchuT and U17ΔchuT colonized internal organs to the same extent as their wild-type strains. The triple mutant ΔchuTΔiroDΔiucD in both E058 and U17 showed decreased pathogenicity compared to each of the single mutants. The histopathological lesions in visceral organs of birds challenged with the wild-type strains were more severe than those from birds challenged with ΔiroD, ΔiucD or the triple mutants. Conversely, chickens inoculated with the ΔchuT mutants had lesions comparable to those in chickens inoculated with the wild-type strains. However, no significant differences were observed between the mutants and the wild-type strains in resistance to serum, cellular invasion and intracellular survival in HD-11, and growth in iron-rich or iron-restricted medium.ConclusionsResults indicated that APEC and UPEC utilize similar iron acquisition mechanisms in chickens. Both salmochelin and aerobactin systems appeared to be important in APEC and UPEC virulence, while salmochelin contributed more to the virulence. Heme bounded by ChuT in the periplasm appeared to be redundant in this model, indicating that other periplasmic binding proteins likely contributed to the observed no phenotype for the heme uptake mutant. No differences were observed between the mutants and their wild-type parents in other phenotypic traits, suggesting that other virulence mechanisms compensate for the effect of the mutations.

Highlights

Avian pathogenic Escherichia coli (APEC) and uropathogenic E. coli (UPEC) are the two main subsets of extraintestinal pathogenic E. coli (ExPEC)
Iron acquisition systems in APEC E058 and UPEC U17 APEC E058 belongs to the O2 serogroup and B2 phylogenetic group, while UPEC U17, isolated from the urine of a patient, was found to belong to the B2 phylogenetic group, but was non-typable by the standard O sera test
Effect of iron acquisition system mutations on chicken virulence Because iron acquisition systems were associated with E. coli isolates from extraintestinal infections, we investigated the importance of distinct iron uptake systems to the virulence of APEC E058 and UPEC U17 in chickens

Summary

Introduction

Avian pathogenic Escherichia coli (APEC) and uropathogenic E. coli (UPEC) are the two main subsets of extraintestinal pathogenic E. coli (ExPEC). Both types have multiple iron acquisition systems, including heme and siderophores. To determine the contribution of each individual iron acquisition system to the virulence of APEC and UPEC, isogenic mutants affecting iron uptake in APEC E058 and UPEC U17 were constructed and compared in a chicken challenge model. Extraintestinal pathogenic Escherichia coli (ExPEC) refers to a group of strains capable of causing diseases outside the intestinal tract, including uropathogenic E. coli (UPEC), sepsis-associated E. coli, and neonatal meningitis-associated E. coli [1]. Avian pathogenic E. coli (APEC) is the main cause of avian colibacillosis, which refers to any localized or systemic infections such as acute fatal septicemia or subacute pericarditis and airsacculitis. As iron exists at low concentrations in extraintestinal sites of infection, the ExPEC strains have evolved multiple strategies for sequestering iron from the host

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