The transcriptional regulator EtrA mediates ompW contributing to the pathogenicity of avian pathogenic Escherichia coli

Abstract

Avian pathogenic Escherichia coli (APEC) causes avian colibacillosis and leads to high mortality in poultry and huge economic losses. Therefore, it is important to investigate the pathogenic mechanisms of APEC. Outer membrane protein OmpW is involved in the environmental adaptation and pathogenesis of Gram-negative bacteria. OmpW is regulated by many proteins, including FNR, ArcA, and NarL. In previous studies, regulator EtrA is involved in the pathogenicity of APEC and affects the transcript levels of ompW. However, the function of OmpW in APEC and its regulation remain unclear. In this study, we constructed mutant strains with altered etrA and/or ompW genes to evaluate the roles of EtrA and OmpW in the biological characteristics and pathogenicity of APEC. Compared with wild-type strain AE40, mutant strains ∆etrA, ∆ompW, and ∆etrA∆ompW showed significantly lower motility, lower survival under external environmental stress, and lower resistance to serum. Biofilm formation by ∆etrA and ∆etrA∆ompW was significantly enhanced relative to that of AE40. The transcript levels of TNF-α, IL1β, and IL6 were also significantly enhanced in DF-1 cells infected with these mutant strains. Animal infection assays showed that deletion of etrA and ompW genes attenuated the virulence of APEC in chick models, and damage to the trachea, heart, and liver caused by these mutant strains was attenuated relative to that caused by the wild-type strain. RT-qPCR and β-galactosidase assay showed that EtrA positively regulates the expression of the ompW gene. These findings demonstrate that regulator EtrA positively regulates the expression of OmpW, and that they both contribute to APEC motility, biofilm formation, serum resistance, and pathogenicity.