Direct and indirect control of Lrp on LEE pathogenicity genes of Citrobacter rodentium

Citrobacter rodentium is a mouse pathogen that, because of its similarities with human enteropathogenic (EPEC) and enterohemorrhagic (EHEC) strains of Escherichia coli is widely used as a model system for in vivo and in vitro studies. Similarly to EPEC and EHEC, C. rodentium carries the LEE (locus of enterocyte effacement) pathogenicity island, encoding virulence factors essential for causing transmissible colonic hyperplasia in mice by attaching and effacing (A/E) lesions. Expression of the genes carried by the LEE pathogenicity island is controlled by complex networks of transcriptional factors, including the global regulators H-NS, IHF, and Fis. In this study, we analyzed the role of Lrp, another global regulator of gene expression in enteric bacteria, on the expression of LEE genes of C. rodentium. To this aim, a real-time PCR approach was used and revealed a negative role of Lrp on the expression of all analyzed LEE genes. Mobility-shift experiments indicated that Lrp action is direct on LEE1 and indirect on all other analyzed LEE genes.