Understanding the expression profile of efflux pumps during the intracellular life of Shigella

In several bacterial pathogens, efflux pumps, besides exporting antimicrobial agents, play a role in bacterial pathogenicity. Shigella, the causative agent of bacillary dysentery, during its evolution towards pathogenicity, has conserved 14, out of 20 present in the genome of its commensal ancestor Escherichia coli, operons encoding efflux pumps systems. The aim of this work is to analyze the induction of efflux pumps conserved in Shigella during the infection of macrophages and epithelial cells and to identify those that are potentially involved in the pathogenesis of Shigella. Our results allowed us to identify efflux pump encoding genes up (mdtJ)- or downregulated (acrA) in macrophages and epithelial cells. Among them, emrK, encoding the membrane subunit of the EmrKY multidrug efflux pump, is specifically up-regulated within macrophages. Moreover, an emrK mutation negatively affects Shigella’s fitness. A deeper analysis of the efflux system EmrKY obtained through GFP assays and microscopy reveals that, while its role is still unknown, EmrKY expression during infection is specific and pH and ion concentration dependent and is mediated by the two-component system EvgA/EvgS.