Proteome response of an extraintestinal pathogenic Escherichia coli strain with zoonotic potential to human and chicken sera

A subset of extraintestinal pathogenic Escherichia coli is zoonotic and has developed strategies to adapt to different host-specific environments. However, the underlying mechanisms of these adaptive strategies have yet to be discerned. Here, the proteomic response of an avian pathogenic E. coli strain, which appears indistinguishable from neonatal meningitis E. coli, was compared following growth in human and avian sera to determine whether it uses the same mechanisms to overcome the antibacterial effects of sera from different host species. Proteins involved in biosynthesis of iron receptors were up-regulated under both sera, suggesting that serum, regardless of the host of origin, is an iron-limited environment. However, several proteins involved in synthesis of nucleic acids, sulfur-containing amino acids and fatty acids, were differentially expressed in response to the sera from different hosts. Mutational analysis showed that this APEC strain required nucleotide biosynthesis during incubation in human, but not avian serum, and deletion of genes involved in the biosynthesis of sulfur-containing amino acids increased its resistance to human serum. Continued investigation of the proteome of 'zoonotic' ExPEC strains, grown under other 'dual' host conditions, will contribute to our understanding of ExPEC pathogenesis and host specificity and development of effective therapies and control strategies.