The non-toxigenic Clostridium difficile CD37 protects mice against infection with a BI/NAP1/027 type of C. difficile strain

Abstract

Clostridium difficile CD37, a clinical isolate from the USA, does not produce toxin A, B or binary toxin. The aim of this study was to determine whether strain CD37 can protect mice against infection from a challenge with a toxigenic C. difficile strain. Three groups of mice (n = 10) were pretreated with a antibiotics cocktail for 5 days, switched to sterile water for 2 days, and given one dose of clindamycin (10 mg/kg) one day (day-1) before challenge (day 0) with a toxigenic C. difficile strain. Group 1 (CD37 + UK6) was given 10(7)C. difficile CD37 vegetative cells by gavage twice a day on days -1 and -2, followed by challenge with 10(6) spores of the toxigenic C. difficile UK6 (BI/NAPI/027) on day 0; Group 2 (UK6) was infected with 10(6)C. difficile UK6 spores on day 0; Group 3 (CD37) was challenged with 10(6) CD37 vegetative cells on day 0. Our data show that pre-inoculation of strain CD37 provided mice significant protection (survival, p < 0.001 between groups CD37 + UK6 and UK6) against subsequent infection with the strain UK6, while mice infected with CD37 only did not develop any symptoms of C. difficile infection (CDI). Our results highlight the potential use of CD37 as a therapeutic strain for the prevention of primary and recurrent CDI in humans.

Fig. 1. Experimental scheme of pretreatment of mice with C. difficile CD37 in a mouse model of C. difficile infection

After 5 days of antibiotic treatment, mice were given autoclaved water for 2 days, followed by a single dose of clindamycin (10 mg/kg) intraperitoneally 1 day before (day-1) challenge with C. difficile UK6 spores by gavage (day 0). The first group (CD37+UK6) was given 10⁷ C. difficile CD37 vegetative cells by gavage twice a day on days -1 and -2, followed by challenge with 10⁶ C. difficile UK6 spores on day 0; the second group (UK6) was infected with 10⁶ C. difficile UK6 spores on day 0; the third group (CD37) was challenged with 10⁶ CD37 vegetative cells on day 0. Mice were monitored for diseases for 7 days.

Fig. 2. Pre-inoculation of C. difficile CD37 protected mice against infection with a virulent strain C. difficile UK6

After challenge with UK6 or CD37, mice were monitored for survival (P <0.001 between groups UK6 and CD37+UK6) (A), weight loss (* p<0.05 on post-infection days 2 and 3 between groups UK6 and CD37+UK6) (B), and occurrence of diarrhea (C). C. difficile toxin levels in feces from group UK6 (D), CD37+UK6 (E) and CD37(F).