Previous research using a recombinant ETBF strain harboring the bft gene in a non-toxigenic B. fragilis (NTBF) strain showed increased polyp formation in the AOM/DSS model compared to the NTBF control group [31], but this increase was less pronounced than that observed with WT-ETBF in the AOM/DSS model. The gene discussed is PITX1; the disease is infectious otitis media.