FIG 5.

Oral immunization with NTCD_mTcd138 spores provided significant protection to hamsters against infection with virulent C. difficile strain UK6 at a dose 200-fold greater than the lethal infection dose. Groups of hamsters (n = 10) were orally immunized with NTCD or NTCD_mTcd138 (2 × 10⁶ spores in 200 μl PBS) or PBS (200 μl) 3 times at 14-day intervals. Seven days after the third immunization, hamsters were given clindamycin (i.p., 40 mg/kg/day for 2 days), followed by infection with 2 × 10⁴ C. difficile UK6 spores by gavage. Hamsters were monitored, and survivals (P = 0.0754 between groups PBS and NTCD; P = 0.0458 between groups PBS and NTCD_mTcd138; P = 0.0899 between groups NTCD and NTCD_mTcd138) (A) and diarrhea (B) were recorded. Animal survivals were analyzed by Kaplan-Meier survival analysis with a log rank test of significance.