Flagella interact with ionic plant lipids to mediate adherence of pathogenic Escherichia coli to fresh produce plants

Bacterial attachment to plant and animal surfaces is generally thought to constitute the initial step in colonization, requiring adherence factors such as flagella and fimbriae. We describe the molecular mechanism underpinning flagella-mediated adherence to plant tissue for the foodborne pathogen, enterohaemorrhagic Escherichia coli. Escherichia coliH7 flagella interacted with a sulphated carbohydrate (carrageenan) on a glycan array, which occurred in a dose-dependent manner. Adherence of E.coliO157:H-expressing flagella of serotype H7, H6 or H48 to plants associated with outbreaks from fresh produce and to Arabidopsis thaliana, was dependent on flagella interactions with phospholipids and sulpholipids in plasma membranes. Adherence of purified H7 and H48 flagella to carrageenan was reduced at higher concentrations of KH₂PO₄ or KCl, showing an ionic basis to the interactions. Purified H7 flagella were observed to physically interact with plasma membranes in spinach plants and in A.thaliana. The results show a specific interaction between E.coliH7, H6 and H48 flagella and ionic lipids in plant plasma membranes. The work extends our understanding of the molecular mechanisms underpinning E.coli flagella targeting of plant hosts and suggests a generic mechanism of recognition common in eukaryotic hosts belonging to different biological kingdoms.