Hcp2b of T6SS affects colonization of avian pathogenic <i>Escherichia coli</i> and host keratin filament expression

T6SS (type VI secretion system) is a type of nano-syringe that exists in APEC (avian pathogenic <i>Escherichia coli</i>). Hcp (haemolysin-coregulated protein) of T6SS participates in the regulation of virulence during APEC infection. However, whether <i>hcp</i> plays a role in bacterial colonization by expression in host cells remains unclear. In this study, we analysed the biological characteristics of the mutant <i>hcp2b</i> strain. Our results showed that the <i>hcp2b</i> gene was involved in the regulation of bacterial motility, biofilm formation, anti-serum and anti-oxidative stress. Moreover, our data indicate that the colonization of the <i>hcp2b</i> mutation strain (Δ<i>hcp2b</i>) in the lung, liver and kidney of chickens decreased significantly. Hence, overexpression of Hcp2b protein in DF-1 cells was used to analyse the effect of Hcp2b on colonization of APEC. Proteomics analysis showed that overexpression of Hcp2b induced differentially expressed proteins in DF-1 cells (230 were significantly upregulated and 96 were significantly downregulated) and differentially expressed proteins were enriched in keratin filament. In conclusion, our data indicated that <i>hcp2b</i> promoted the colonization of APEC by affecting the expression of keratin filament.