Fig. 2. Expression and role of ler during C. rodentium infection in SPF and GF mice.

A, ler mRNA levels were determined by qPCR in fecal pellets of SPF and GF mice infected with C. rodentium at the indicated days post-infection. Expression was normalized to that of the kanamycin resistance gene carried by the C. rodentium strain. Control experiments were performed by determining ler mRNA levels in C. rodentium grown under inducing (DMEM) and repressing (LB) in vitro culture conditions (4, 10). Data represent mRNA expression relative to that in C. rodentium cultured in LB medium. Results are given as mean ± SD of individual mice (n=3). Results are representative of at least 2 experiments. *; p<0.05, ***; p<0.001 by Dunnett's multiple comparison test. B, Expression of ler in fecal pellets of SPF and GF mice infected with the reporter ler-lux C. rodentium strain at the indicated day post-infection. Results show luminescence (relative light units) and cfu of ler-lux C. rodentium in the same samples. Data expressed as mean ± SD of individual mice (n=4). Results are representative of at least 2 experiments. C, Bioluminescent imaging of ler expression in the intestines of SPF and GF mice infected with the ler-lux C. rodentium strain. Imaging was performed on day 5 and 14 post-infection and the signal was quantified based on the color scale shown below. Results are representative of 3 individual mice. D, SPF and GF mice (n= 5) were infected orally with 10⁹cfu of WT and Δler mutant C. rodentium, and pathogen load in feces was determined over the indicated time. Data points are given as mean ± SD. Results are representative of at least 2 experiments. E, GF mice were infected with WT and Δler mutant C. rodentium. At day 3 or day 21 post infection, mice were co-housed with SPF mice (1:1). Pathogen load was determined in feces on indicated days after co-housing. Dots represent individual mice. Results are representative of at least 3 experiments. N.S., not significant, *; p<0.05, **; p<0.01 by Dunn's test.