Aerobactin Synthesis Genes iucA and iucC Contribute to the Pathogenicity of Avian Pathogenic Escherichia coli O2 Strain E058

Aerobactin genes are known to be present in virulent strains and absent from avirulent strains, but contributions of iucC and iucA, which are involved in aerobactin synthesis, to the pathogenicity of avian pathogenic Escherichia coli (APEC) have not been clarified. In this study, effects of double mutants (iucA/iutA or iucC/iutA) compared to those of single mutants (iucA, iucC or iutA) of aerobactin genes on the virulence of APEC strain E058 were examined both in vitro (aerobactin production, ingestion into HD-11 cells, survival in chicken serum) and in vivo (competitive growth against parental strain, colonization and persistence). In competitive co-infection assays, compared to the E058 parental strain, the E058 Delta iucA mutant was significantly reduced in the liver, kidney, spleen (all P<0.01), heart and lung (both P<0.001). The E058 Delta iutA mutant also was significantly reduced in the liver, lung, kidney (all P<0.01), heart and spleen (both P<0.001). The E058 Delta iucC mutant was significantly attenuated in the heart and kidney (both P<0.05) and showed a remarkable reduction in the liver, spleen and lung (P<0.01); meanwhile, both E058 Delta iucA Delta iutA and E058 Delta iucC Delta iutA double mutants were sharply reduced as well (P<0.001). In colonization and persistence assays, compared with E058, recovered colonies of E058 Delta iucA were significantly reduced from the lung, liver, spleen and kidney (P<0.01) and significantly reduced in the heart (P<0.001). E058 Delta iutA was significantly reduced from the heart, lung, liver, spleen and kidney (P<0.01). E058 Delta iucC, E058 Delta iucA Delta iutA and E058 Delta iucC Delta iutA were significantly decreased in all organs tested (P<0.001). These results suggest that iutA, iucA and iucC play important roles in the pathogenicity of APEC E058.