FIG. 6.

Role of F9 fimbriae in colonization of the terminal rectum of weaned cattle. (A) Seven calves were orally challenged with E. coli O157:H7 (Nal^r) having a defined deletion of the Z2200 gene (the F9 main fimbrial subunit gene). The mean shedding levels per gram of feces for the mutant (⋄) were compared with the mean values resulting from oral challenges with the parent strain (▪) (data based on 19 orally colonized animals [see Materials and Methods]). Estimated 95% confidence intervals (means ± 2 standard errors) are indicated. (B) Fecal surface-to-core ratios for E. coli O157:H7 CFU as an indicator of terminal rectal colonization. Each symbol indicates data for an individual animal. A log₁₀ surface-to-core ratio of 0 indicates equivalent distribution, and this result was obtained for the majority of the early samples (days 1 to 3). As colonization was established over days 4 to 10, the ratio increased as localization developed.