FIG 8.

(A and B) Soft agar containing a suspension of PA2 was overlaid onto LB and allowed to solidify, and fecal supernatants from infected mice were spotted onto the overlay. Plates were incubated overnight at 37°C. (A) Fecal supernatants from mice cocolonized with 0.1229 and PA2 prevented the growth of PA2, resulting in a zone of clearing in the soft agar. (B) Supernatants from mice colonized with 0.1229ΔB17::FRTΔmctAB::cat did not affect PA2 growth. (C) PA2 colonization in cocolonized mice. PA2 colonization was detectable in only 17% of mice cocolonized by wild-type 0.1229 and in none of the mice colonized by 0.1229 ΔmctAB::cat, 0.1229ΔB17::FRT, or 0.1229ΔB17::FRT ΔmctAB::cat. In contrast, 100% of mice inoculated with PA2 alone became colonized (also see Table 3). (D) Low colonization levels did not affect Stx production. Stx was detected in all mouse groups, and concentrations ranged from 18 to 900 ng/mL. There were no differences between groups.