a–h, Groups of CD-1 mice were mock-infected; infected intragastrically with the wild type, the ∆ctx mutant or the ∆ctx mutant mixed with purified CTX (CT); or treated orally with purified CTX. Samples were collected one day after infection. a, Representative images of H&E-stained ileum tissue sections showing capillary congestion (arrows) from mice that were infected with the indicated strains or treated orally with purified CTX. All images were taken at 60× magnification. b, Expression of Cxc1 and Cxcl2 in the ileal mucosa of mice (n = 4) was determined by RT–qPCR analysis. Data represent mean ± s.d. of Cxcl1 and Cxcl2 mRNA levels as fold change over mRNA levels in mock-infected mice. An unpaired two-sided Student’s t-test was used to compare the difference in fold change between wild-type and ∆ctx-mutant V. cholerae. c, Fluid accumulation ratios for mice treated with the indicated strains or treated orally with purified CTX (n = 8 for wild type, ∆ctx and mock; n = 4 for CTX and ∆ctx + CTX; n = 5 for wild type and ∆ctx 6 h post-infection (p.i.)). The fluid accumulation ratios between groups were compared using a one-way ANOVA (F 6,35 = 66.03, P < 0.0001) followed by Tukey’s multiple comparisons test. Lines represent median; black dots are individual mice. Different shapes indicate mice from different litters. d, Luminal haemin measurements from the ileum of mice (n = 4) treated with the indicated strains or treated orally with purified CTX. Haemin levels in the CTX-treated group were compared to the ∆ctx mutant and mock using a one-way ANOVA (F 3,12 = 25.59, P < 0.0001) followed by Sidak’s multiple comparisons test. Lines represent median; black dots are individual mice. e, CFU per g and total CFU from the whole gastrointestinal tract (gut) from mice (n = 4) infected with wild-type or ∆ctx-mutant V. cholerae. An unpaired two-sided Student’s t-test was used to compare the bacterial concentrations from wild-type- and ∆ctx-mutant-infected mice. Data represent mean ± s.d. f, CFU per g of tissue (ileum) (n = 4) and total CFU from the lumen of the ileum (n = 11 for wild type; n = 9 for ∆ctx; n = 4 for ∆ctx + CTX) or lumen of the caecum (n = 8 for wild type; n = 7 for ∆ctx; n = 4 for ∆ctx + CTX) from mice infected with the indicated V. cholerae strains. An unpaired two-sided Student’s t-test was used to compare the CFU per g of tissue in wild-type- and ∆ctx-mutant-infected mice. The CFU in the ileum or caecum for the wild-type-infected groups were compared to the ∆ctx-mutant- or mock-infected groups using a one-way ANOVA (ileum: F 2,21 = 50.24, P < 0.0001; caecum: F 2,16 = 51.6, P < 0.0001) followed by Sidak’s multiple comparisons test. Data represent mean ± s.d. g, CFU in the lumen of the ileum in mice 6 h after infection with V. cholerae. An unpaired two-sided Student’s t-test was used to compare the CFU from wild-type- and ∆ctx-mutant-infected mice. Data represent mean ± s.d. Different shapes or different coloured shapes indicate mice from different litters (f, g). h, Measurements of luminal LCFAs (8-carbon chain or longer) from the ileum of mice that were treated with the indicated strains or treated orally with purified CTX (n = 3 for wild type, ∆ctx and mock; n = 4 for CTX). LCFA concentrations in the CTX-treated group were compared to the ∆ctx-mutant- and mock-infected groups using a one-way ANOVA (F 3,9 = 7.814, P = 0.0071) followed by Sidak’s multiple comparisons test. Lines represent median; black dots are individual mice. This figure is related to Figs. 1–3. Source data