Transposon mutagenesis identifies the sspA-sspB operon as essential for serum resistance and virulence in avian pathogenic Escherichia coli.

Abstract

Avian pathogenic Escherichia coli (APEC) constitutes a significant threat to poultry health worldwide, causing colibacillosis and inflicting substantial economic losses. The ability to resist serum-mediated killing is a key virulence factor enabling APEC to circumvent the host immune system and establish systemic infection. In this study, we employed mariner-based transposon mutagenesis to generate a mutant library of APEC strain E058 and screened for mutants with reduced serum resistance. We identified a transposon insertion within the sspB gene of the sspA-sspB operon that conferred significantly reduced serum resistance. Targeted gene knockout experiments confirmed that both sspA and sspB contribute to serum resistance, with the double mutant (ΔsspAΔsspB) displaying a more pronounced susceptibility to serum compared to the single gene knockouts (ΔsspA and ΔsspB). Furthermore, in vivo challenge experiments in chickens demonstrated that disruption of the sspA-sspB operon significantly attenuated APEC virulence. Our study also reveals that the sspA-sspB operon plays a role in biofilm formation and promotes intracellular survival within macrophages, suggesting a multifaceted contribution to APEC pathogenesis. These findings highlight the sspA-sspB operon as a promising target for the development of novel therapeutics against APEC infections in poultry.