Dextran sodium sulfate (DSS‐colitis in B6 mice is associated with IgA‐uncoated bacteria. B6 mice treated with DSS without antibiotic treatment [B6 + DSS], after 4 weeks of antibiotic treatment [B6‐Abx+DSS], after antibiotic treatment and B6 fecal transplantation (FT) [B6‐Abx+B6FT+DSS], and after antibiotic treatment and CBA FTs [B6‐Abx+CBAFT+DSS] (a). B6 mice treated with DSS without antibiotic treatment [B6+DSS], after antibiotic treatment [B6‐Abx+DSS], after antibiotic treatment and FTs with homologous IgA‐coated bacteria [B6‐Abx (A+ve FT)+DSS], and after antibiotic treatment and FTs with homologous IgA‐uncoated bacteria [B6‐Abx (A‐ve FT)+DSS] (b). CBA mice treated with DSS without antibiotic treatment [CBA+DSS], after antibiotic treatment [CBA‐Abx+DSS], after antibiotic treatment and B6 FTs [CBA‐Abx+B6FT+DSS], and after antibiotic treatment and CBA FTs [CBA‐Abx+CBAFT+DSS] (c). Data are representative of four experiments (a) and two experiments (b, c) with fecal pellets pooled from seven or eight mice for each IgA+/− separation.