Backgrounds: Clostridium difficile infection (CDI) a toxin-mediated disease of the colon and remains a major clinical burden to global healthcare systems. C. difficile virulence is primarily attributed to the production of large clostridial toxins TcdA (toxin A) and TcdB (toxin B), thus therapeutic strategies which reduce toxin production and activity can significantly decrease the pathogenicity of CDI and improve patient outcomes. This study investigated the effect of a range of natural products on toxin production and activity of C. difficile in vitro.
Objective: To investigate the effect of a range of natural products on the production and activity of C. difficile toxins in vitro.
Methods: Twenty-two natural products were investigated against four C. difficile strains. The toxin protection activity of products was determined using Vero and HT-29 cell cytotoxicity and neutral red uptake assays. Indirect effect of products on toxin-mediated cytotoxicity was determined using the same cell lines. Based on the results from toxin activity assays, seven out of the 22 products were selected to determine their effects on toxin production of C. difficile using ELISA.
Results: Zingerone (0.3 mg/ml) protected both Vero and HT-29 cells from C. difficile cytopathic effects, confirmed by a neutral red uptake assay (P < 0.05). The three Western Australian Leptospermum honeys (4% w/v), onion juice (12.5% v/v) and trans-cinnamaldehyde (0.005% v/v) reduced both toxin production and activity of C. difficile significantly (P ≤ 0.023). Garlic powder (4.7 mg/ml) also showed a significant reduction in toxin activity (P ≤ 0.047), but had no effect on toxin production.
Conclusions: Five out of 22 natural products reduced both C. difficile toxin production and activity in vitro. Zingerone showed protection against the cytopathic effect of C. difficile toxins likely through blocking either the toxin binding sites on the toxin molecule or the host cell receptors.
Significance and Impact of the Study: This study encourages further investigation of natural products against C. difficile toxins in vivo.