FIG 2.

Oral immunization with NTCD_mTcd138 spores provided full protection to mice against infection with hypervirulent C. difficile strain UK6. Groups of mice (n = 10) were orally immunized with spores of NTCD or NTCD_mTcd138 (2 × 10⁶ spores in 200 μl PBS) or with PBS (200 μl) 3 times at 14-day intervals. Seven days after the third immunization, mice were given an antibiotic mixture in drinking water for 4 days, switched to regular water for 2 days, and given one dose of clindamycin (10 mg/kg) before infection with 10⁶ C. difficile UK6 spores by gavage. Mice were monitored, and mouse survival (P = 0.495 between groups PBS and NTCD; P = 0.0002 between groups PBS and NTCD_mTcd138; P = 0.002 between groups NTCD and NTCD_mTcd138) (A), mean relative weight changes (P = 0.0004 between groups NTCD and NTCD_mTcd138; P = 0.2366 between groups PBS and NTCD) (B), and frequency of diarrhea (C) of different groups were recorded. Animal survivals were analyzed by Kaplan-Meier survival analysis with a log rank test of significance. Bars show means ± SD. (*, P < 0.05; ns, no significance, P > 0.05).