(A) Competitive index (CI) of the EcN wild type (WT) and the moaA mutant after anaerobic growth in mucin broth supplemented with 40 mM of the indicated electron acceptors (N = 3). (B) Mock-treated mice (Mock), DSS-treated mice (DSS) or mice treated with DSS and AG (DSS+AG) were inoculated with the indicated mixtures of E. coli strains and the CI in colon contents determined 5 days after inoculation. A plasmid (pMOA1) carrying the cloned moaA gene was used to complement the moaA mutant (moaA). N is given in . (C) Concentration of nitrate (NO₃^-) determined in the cecal mucus layer of mock-treated mice (N = 4), DSS-treated mice (DSS, N = 3) or mice treated with DSS and AG (DSS+AG, N = 4). Bars represent geometric means ± standard error. *, P < 0.05; **, P < 0.01; ***, P < 0.001; ns, not statistically significant (Student’s t-test).

Mock-treated (Mock), DSS-treated (DSS) or DSS+AG-treated (DSS+AG) wild-type mice, Nos2-deficient mice (Nos2) or mice harboring T cells deficient for the production of IL-10 (Cd4 Il10 mice) were inoculated with the indicated mixtures of E. coli strains. WT, E. coli wild type; narG narZ napA, E. coli nitrate respiration-deficient mutant. The narG narZ napA mutant was complemented by introducing a functional chromosomal napA allele and a plasmid (pNARG1) carrying the cloned narG gene (narG narZ napA[rest] [pNARG1]). Pathological changes in the colon (A and C) and the competitive index (CI) recovered from colon contents (B and D) were determined 5 days after inoculation. (A and C) Combined histopathology score in the colon. Each dot represents data from an individual animal. Experiments were performed with EcN (A-B) or E. coli LF82 (C-D). (B and D) Bars represent geometric means ± standard error. **, P < 0.01; ***, P < 0.001 (Student’s t-test). N is given in panels A and C.

(A-D) Bovine ligated ileal loops treated with thapsigargin or mock-treated (vehicle) were inoculated with a mixture of EcN (WT) and a nitrate respiration-deficient mutant (narG napA narZ). Samples were collected 8 hours after inoculation. (A) Representative H&E stained ileal sections. Scale bar, 200 μm. (B) Combined histopathology score in the ileum. Each dot represents data from an individual animal. (C) Fluid accumulation in ligated ileal loops. (D) Competitive indices (CI) recovered from the luminal fluid (open bars) or mucus scrapings (closed bars). (E-H) DSS-treated mice were inoculated either with EcN (WT) or with the narG napA narZ mutant. Inflammation in the colon (E, F and G) and bacterial numbers recovered from colon contents (E) were determined 5 days after inouclation. (E) Representative H&E stained colonic sections. Scale bar, 100 μm. (F) Combined histopathology score in the colon. (G) Expression of Nos2, Kc and Tnfa in colonic RNA samples using qRT-PCR (fold-increases over mock-treated, mock-treated mice). (H) Bacterial numbers (CFU) recovered from colon contents. (C, D, G, H) Bars represent geometric means ± standard error. *, P < 0.05; **, P < 0.01; ns, not statistically significant (Student’s t-test). N is given in panels B and F.