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AIMS: To investigate the mechanisms of action of natural products with bactericidal (cinnamon root powder, peppermint oil, trans-cinnamaldehyde, menthol and zingerone) or bacteriostatic (fresh garlic bulb extract, garlic clove powder, Leptospermum honey and allicin) activity against two Clostridium difficile strains. METHODS AND RESULTS: Bactericidal products significantly reduced intracellular ATP after 1 h (P ≤ 0·01), quantified using the BacTiter-Glo reagent, and damaged the cell membrane, shown by the leakage of both 260-nm-absorbing materials and protein, and the uptake of propidium iodide. Bacteriolysis was not observed, determined by measuring optical density of treated cell suspensions at 620-nm. The effect of three bacteriostatic products on protein synthesis was quantified using an Escherichia coli S30 extract system, with Leptospermum honey (16% w/v) showing significant inhibition (P < 0·01). Lastly, no products showed elevated minimum inhibitory concentrations against antimicrobial-resistant C. difficile, determined by broth microdilution. CONCLUSIONS: Cytoplasmic membrane damage was identified as a mechanism of action that may contribute to the activity of several natural products against C. difficile. SIGNIFICANCE AND IMPACT OF THE STUDY: This study describes the possible mechanisms of action of natural products against C. difficile, yet the efficacy in vivo to be determined.
Roshan et al. (Fri,) studied this question.