(a) Mice were infected with an equal mixture of AIEC strains LF82 and NRG857c, and individual AIEC populations were enumerated in faecal output. Each data point represents the competitive index from an individual animal. Solid lines indicate the geometric mean for each group (n=5). (b) Quantification of AIEC in faeces of monocolonized mice. *P<0.05; **P<0.01 (Mann–Whitney’s test). Data are means with s.e. from four to nine mice per group from two experiments. (c) IHC analysis of caecal sections 28 days after infection with NRG857c and in PBS controls. Tissue was fixed and processed for IHC staining using an antibody directed against the O83 antigen found on AIEC strain NRG857c (brown stain in images). Images are representative from two separate experiments. Scale bar, 200 μm.