Galactomannan and Vicilin from Fenugreek Seeds (Trigonella foenum-graecum) Impair Early Pathogen-Host Interaction of Campylobacter jejuni with Intestinal Cells via JlpA

Campylobacter jejuni is the leading cause of severe enteritis worldwide. Identification of natural products against C. jejuni that inhibit early-stage host-pathogen interactions is a promising strategy, particularly by blocking bacterial adhesion to and invasion into the host cells. This should help to reduce the bacterial load in vector animals. From the seeds of Trigonella foenum-graecum, an aqueous extract (fenugreek high molecular fraction) of high-molecular compounds (polysaccharides, proteins) was obtained. The polysaccharide was characterized as galactomannan (1,4-mannose backbone, substituted at O-6 with single galactose residues and galactose oligosaccharide chains). The protein part consisted of 50 kDa vicilin as the main compound. The fenugreek high molecular fraction did not influence proliferation of C. jejuni and viability of Caco-2 cells (1 - 1000 µg/mL). The fenugreek high molecular fraction reduced bacterial adhesion to Caco-2 significantly (500 - 1000 µg/mL), which was due to an interaction with the bacterial adhesin JlpA, preventing the interaction of this outer membrane protein to its ligand HSP90α (IC₅₀ = 23.4 µg/mL). Bacterial invasion was reduced significantly. Both polysaccharides as well as vicilin contribute to the observed antiadhesive effect. As vicilin-like proteins are widely found in plants from the Fabaceae family, a vicilin-enriched protein preparation from Pisum sativum was investigated for antiadhesive activity. These findings suggest that fenugreek seeds or vicilin-rich plant extracts could be used to develop novel strategies to control C. jejuni infections in food-producing animals, ultimately helping to decrease the prevalence of campylobacteriosis in humans.