FIG. 9.

E. coli O157 colonization patterns at the RAJ mucosa among rectally dosed cattle. Four 4- to 9-month-old Holstein steers were given a single rectal dose containing 10¹⁰ CFU of both the wild type and the filament mutant on day zero. Colonization was assessed by direct (quantitative) and enrichment (qualitative) RAMS cultures. Bar heights represent total E. coli O157 CFU/swab. Samples positive only by enrichment culture had ≤2.8 × 10¹ CFU/swab and are shown as E+. No bar indicates an E. coli O157 culture-negative sample. For each positive sample, 20 to 100 isolates were subcultured on motility agar to determine the proportions that were mutant (checkered bar) or wild-type (filled bar) isolates recovered.