ExPEC strains colonize the mouse intestine. (A to C) BALB/c mice were subjected to oral gavage with ExPEC CP9 at different doses (109,107,105, and 103 CFU). (B) Intestinal colonization was monitored by plating fecal pellets on LB/agarChlor+ and selecting for CP9 E. coli (chloramphenicol resistant). (C) Mice were euthanized on day 15, and intestinal tissue colonization was determined by sectioning and plating on LB/agarChlor+. Symbols represent individual mice within groups and are shaded accordingly. Error bars represent ± standard deviations, and n was at least 3.