<i>ybjX</i> mutation regulated avian pathogenic <i>Escherichia coli</i> pathogenicity though stress-resistance pathway

<i>ybjX</i> gene mutation decreased the pathogenicity of the avian pathogenic <i>Escherichia coli</i> strain, AE17. However, the associated regulatory mechanism of <i>ybjX</i> 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 <i>ybjX</i> mutations with those of the wild strain and studied the effects of <i>ybjX</i> on miRNA expression in the spleen. Our findings revealed that the mutant strain, Δ<i>ybjX</i>, 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 <i>ybjX</i> mutation reduced stress resistance by down-regulating mRNAs in metabolic pathways. Infection with the <i>ybjX</i> 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 <i>ybjX</i> mutation reduces serum, blood, and environmental stress resistance by down-regulating the mRNA in metabolic pathways.