Pentatricopeptide repeat protein EspX1 facilitates the virulence of avian pathogenic Escherichia coli

Avian pathogenic Escherichia coli (APEC) can infect poultry and cause colibacillosis, leading to significant economic losses in the poultry industry. APEC is similar to human Extraintestinal pathogenic Escherichia coli (ExPEC) in serotype, phylogenetic clustering and virulence genes, and is a repository of ExPEC virulence and drug resistance genes. We identified a pentatricopeptide repeat (PPR) protein EspX1 in APEC, but its function is unknown. The espX1 gene mutant and complemented strains of APEC were constructed and characterized. The results showed that EspX1 does not affect the growth or motility of APEC. The espX1 deletion mutant exhibited enhanced biofilm formation and cell adhesion but reduced serum resistance and intracellular survival. Furthermore, the mutant strain showed decreased colonization in the liver and spleen during systemic infection and attenuated virulence in vivo. Additionally, EspX1 was found to inhibit the expression of inflammatory cytokines TNF-α, IL-1β, and IL-8 in host cells. These findings suggest that EspX1 plays a crucial role in the pathogenicity of APEC by modulating multiple virulence-related phenotypes and host immune responses. In addition, EspX1 enhances APEC resistance to ciprofloxacin. This study provides novel insights into the functions of PPR proteins in prokaryotes and lays a theoretical foundation for developing new strategies to control APEC infections.