Graphene-Coated Surface Plasmon Resonance Interfaces for Studying the Interactions between Bacteria and Surfaces

A variety of physical and chemical parameters are of importance for adhesion of bacteria to surfaces. In the colonization of mammalian organisms for example, bacterial fimbriae and their adhesins not only seek particular glycan sequences exposed on diverse epithelial linings, they also enable the bacteria to overcome electrostatic repulsion exerted by their selected surfaces. In this work, we present a new technique based on simplified model systems for studying the adhesion strength of different Escherichia coli strains. For this purpose, gold-based surface plasmon resonance (SPR) interfaces were coated with thin films of reduced graphene oxide (rGO) through electrophoretic deposition. The rGO matrix was post-modified with polyethyleneimine (PEI), poly(sodium 4-styrenesulfonate) (PSS), mannose, and lactose through pi-stacking and/or electrostatic interactions by simple immersion of the SPR interface into their respective aqueous solutions. The adhesion behaviors of one uropathogenic and two enterotoxigenic Escherichia coli clinical isolates, that each express structurally characterized fimbrial adhesins, were investigated. It was found that the UTI89 cystitis isolate that carries the mannose-binding FimH adhesin was most attracted to the PEI- and mannose-modified surfaces, whereas the att25 diarrhoeal strain with the N-acetylglucosamine-specific F17a-G adhesin disintegrated the lactose-modified rGO. The highly virulent 107/86 strain interacted strongly with the PSS-modified graphene oxide, in agreement with the polybasic surroundings of the ABH blood group-binding site of the FedF adhesin, and showed a linear SPR response in a concentration range between 1 X 10(2) and 1 X 10(9) cfu/mL.