The two-component system, BasSR, is involved in the regulation of biofilm and virulence in avian pathogenic <i>Escherichia coli</i>

Abstract

Avian pathogenic <i>Escherichia coli</i> (APEC) is a subgroup of extra-intestinal pathogenic <i>E. coli</i> (ExPEC) strains that cause avian colibacillosis, resulting in significant economic losses to the poultry industry worldwide. It has been reported that a few two-component signal transduction systems (TCS) participate in the regulation of the virulence factors of APEC infection. In this study, a <i>basSR</i>-deficient mutant strain was constructed from its parent strain APECX40 (WT), and high-throughput sequencing (RNA-seq) was performed to analyse the transcriptional profile of WT and its mutant strain XY1. Results showed that the deletion of <i>basSR</i> down-regulated the transcript levels of a series of biofilm- and virulence-related genes. Results of biofilm formation assays and bird model experiments indicated that the deletion of <i>basSR</i> inhibited biofilm formation <i>in vitro</i> and decreased bacterial virulence and colonization <i>in vivo</i>. In addition, electrophoretic mobility shift assays confirmed that the BasR protein could bind to the promoter regions of several biofilm- and virulence-related genes, including <i>ais</i>, <i>opgC</i> and <i>fepA</i>. This study suggests that the BasSR TCS might be a global regulator in the pathogenesis of APEC infection. <b>RESEARCH HIGHLIGHTS</b> Transcriptional profiling showed that BasSR might be a global regulator in APEC. BasSR increases APEC pathogenicity <i>in vivo</i>. BasSR positively regulates biofilm- and the virulence-associated genes. BasSR can bind to the promoter regions of virulence-associated genes <i>ais</i>, <i>opgC</i> and <i>fepA</i>.