Expression profile of EmrKY efflux pumps during Shigella's intracellular life

Backgrounds In several bacterial pathogens, efflux pumps, besides exporting antimicrobial agents, play a role in bacterial pathogenicity. Shigella, the causative agent of bacillary dysentery, has conserved 14 out of 20 operons encoding efflux pumps systems present in the genome of its commensal ancestor Escherichia coli. Objectives The aim of this work was (i) to analyze the regulation of Shigella's efflux pumps during the infection of macrophages and epithelial cells and (ii) to identify and characterize those that are required for bacterial pathogenesis. Methods The expression of efflux pumps was monitored by qRT-PCR during infection of macrophages and epithelial cells. Strains defective for efflux pump encoding genes were used in infection assays to investigate the existence of interplays between them. Competition assays were conducted to compare the importance of these genes in Shigella’s fitness. To better understand the regulative network, transcriptional fusions were monitored in the presence of different stimuli which reflect the intracellular environment. Conclusions Our results allowed us to identify efflux pump encoding genes up- or downregulated in macrophages and epithelial cells. Among them, emrK, encoding the membrane subunit of the EmrKY multidrug efflux pump, was specifically up-regulated within macrophages. Moreover, an emrK mutation was shown to affect Shigella’s fitness. Our observations also reveal that its role, still unknown, and its modulation during infection are dependent upon pH and ion concentrations.