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

Abstract

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 < 0·01). Sporicidal activity, investigated using a standard plate recovery assay, was minimal.

Conclusions: Three of the 22 natural products (13%) showed inhibitory effects on sporulation of C. difficile and six products (27%) reduced vegetative outgrowth of C. difficile.

Significance and impact of the study: This study shows the potential of natural products to inhibit different stages of C. difficile sporulation and encourages further investigation in this field.

Keywords: Clostridium difficile spores; alternative therapy; germination; outgrowth; sporulation.