ybjX mutation regulated avian pathogenic Escherichia coli pathogenicity though stress-resistance pathway.

ybjX gene mutation decreased the pathogenicity of the avian pathogenic Escherichia coli strain, AE17. However, the associated regulatory mechanism of ybjX remains unknown. In this study, we examined the bactericidal activity of chicken serum and blood, as well as bacterial survival in HD11 macrophages. We compared the transcriptome of ybjX mutations with those of the wild strain and studied the effects of ybjX on miRNA expression in the spleen. Our findings revealed that the mutant strain, ΔybjX, had a lower resistance to chicken serum and blood, as well as lower bacterial survival in HD11 macrophages than AE17. RNA sequencing analyses showed that the ybjX mutation reduced stress resistance by down-regulating mRNAs in metabolic pathways. Infection with the ybjX mutant strain caused changes in the splenic miRNA profile. We verified Kelch repeat and BTB domain-containing protein 11 to be the target of miR-133b. Together, these findings suggest that the ybjX mutation reduces serum, blood, and environmental stress resistance by down-regulating the mRNA in metabolic pathways.