Citrobacter rodentiumRelies on Commensals for Colonization of the Colonic Mucosa

We investigated the role of commensals at the peak of infection with the colonic mouse pathogen Citrobacter rodentium.Bioluminescent and kanamycin (Kan)-resistant C. rodentiumpersisted avirulently in the cecal lumen of mice continuously treated with Kan. A single Kan treatment was sufficient to displace C. rodentiumfrom the colonic mucosa, a phenomenon not observed following treatment with vancomycin (Van) or metronidazole (Met). Kan, Van, and Met induce distinct dysbiosis, suggesting C. rodentiumrelies on specific commensals for colonic colonization. Expression of the master virulence regulator leris induced in germ-free mice, yet C. rodentiumis only seen in the cecal lumen. Moreover, in conventional mice, a single Kan treatment was sufficient to displace C. rodentiumconstitutively expressing Ler from the colonic mucosa. These results show that expression of virulence genes is not sufficient for colonization of the colonic mucosa and that commensals are essential for a physiological infection course.