FIG 6.

C. difficile pilus mutants are outcompeted by the parental strain in murine coinfections. Mice were inoculated with mixed inoculums containing ∼10⁵ spores of each strain. Feces was collected every 2 days starting 1 day postinoculation and plated on TCCFA (total spores) and TCCFA with erythromycin (mutant spores only) to determine bacterial burdens. Competitive indices (mutant to parent) for the competition between 630Δerm and pilA1 mutant (A), 630Δerm and pilB1 mutant (B), and 630Δerm and tcdR mutant (C). Data were excluded if in total fewer than 10 spores were recovered. Symbols represent CI values from individual animals, and error bars indicate the standard deviations. Data were analyzed by the Wilcoxon rank sum test comparing values to a hypothetical CI of 1 indicating no difference. *, P < 0.05; **, P < 0.01; ***, P < 0.001.