Effects of natural products on several stages of the spore cycle of Clostridium difficile in vitro

Aims To investigate the effect of natural products on the spore cycle of Clostridium difficile in vitro. Methods and Results Twenty‐two natural products were investigated using four C. difficile strains. Effects on sporulation, determined using microscopy and a conventional spore recovery assay, showed that fresh onion bulb extract (6·3% v v−1) and coconut oil (8% v v−1) inhibited sporulation in all four isolates by 66–86% and 51–88%, respectively, compared to untreated controls. Fresh ginger rhizome extract (25% v v−1) was also inhibitory, although to a lesser extent. Using a standard spore germination and outgrowth assay, germination was unaffected by the 22 products, whereas outgrowth was significantly reduced by artichoke extract (18·8 mg ml−1), fresh onion bulb extract (25% v v−1), Leptospermum honeys (8% w v−1) and allicin (75 mg ml−1; P