The avian pathogenic Escherichia coli O2 strain E058 carrying the defined aerobactin-defective iucD or iucDiutA mutation is less virulent in the chicken.

The expression of aerobactin accounts for much of the pathogenesis of avian pathogenic Escherichia coli (APEC). iucA , iucB , iucC and iucD are involved in aerobactin synthesis and iutA is responsible for the expression of a specific outer membrane receptor protein for ferric aerobactin. Knockout mutants of iucD and iucDiutA in the APEC O2 strain E058 were constructed and named E058Δ iucD and E058Δ iucD Δ iutA , respectively. To evaluate the pathogenicity of these mutants, we used multiple approaches to assess the effects of mutations on the virulence of APEC E058. Aerobactin-defective mutants E058Δ iucD and E058Δ iucD Δ iutA showed significantly decreased pathogenicity compared with the wild-type strain E058, evidenced by the low extent of colonization in selected organs or being outcompeted by E058 in vivo . Chickens challenged with APEC E058 exhibited typical signs and lesions of avian colibacillosis, while those inoculated with the mutants E058Δ iucD or E058Δ iucD Δ iutA showed moderate airsacculitis, mild pericarditis and perihepatitis. However, no significant differences in resistance to specific-pathogen-free chicken serum, ingestion by HD-11 cells, and growth rates in LB were observed between the mutants and the wild-type strain. These results indicated that the IucD- and IutA-related virulence factors play a significant role in the pathogenesis of the APEC strain E058. [ABSTRACT FROM AUTHOR]