Adhesion is a prerequisite for bacteria to colonize cell surfaces. To accomplish cellular adhesion, many bacteria use carbohydrate‐specific lectins, which are expressed as part of capillary protein appendages expanding from their surface, called fimbriae or pili. For bacteria, colonization of cell surfaces offers advantageous conditions to persist and multiply. For the host, however, bacterial colonization can be affiliated with severe health problems such as inflammation. Therefore, to combat bacterial adhesion and inflammatory diseases, investigation of the molecular and biophysical details of the relevant lectin–carbohydrate interactions is important. Understanding molecular carbohydrate recognition can lead to the development of high‐affinity inhibitors of bacterial lectins. That way, interfering with the bacterial attachment to surfaces proves the vision of an antiadhesion therapy, among others, against uropathogenic E. coli (UPEC). One of the most important and best investigated bacterial lectins is the mannose‐specific protein FimH, which is expressed on the tips of type 1 fimbriae. During the last 30 years, many natural as well as synthetic mannosidic ligands of FimH have been designed and tested for their inhibitory potencies. We report key results and comment on key problems and perspectives of this research.

The detection and removal of bacteria, such as E. coli in aqueous environments by using safe and readily available means is of high importance. Here we report on the synthesis of nanodiamonds (ND) covalently modified with specific carbohydrates (glyco-ND) for the precipitation of type 1 fimbriated uropathogenic E. coli in solution by mechanically stable agglutination. The surface of the diamond nanoparticles was modified by using a Diels-Alder reaction followed by the covalent grafting of the respective glycosides. The resulting glyco-ND samples are fully dispersible in aqueous media and show a surface loading of typically 0.1 mmol g(-1). To probe the adhesive properties of various ND samples we have developed a new sandwich assay employing layers of two bacterial strains in an array format. Agglutination experiments in solution were used to distinguish unspecific interactions of glyco-ND with bacteria from specific ones. Two types of precipitates in solution were observed and characterized in detail by light and electron microscopy. Only by specific interactions mechanically stable agglutinates were formed. Bacteria could be removed from water by filtration of these stable agglutinates through 10 μm pore-size filters and the ND conjugate could eventually be recovered by addition of the appropriate carbohydrate. The application of glycosylated ND allows versatile and facile detection of bacteria and their efficient removal by using an environmentally and biomedically benign material.

A combination of microtiter plate functionalization techniques and two facile bacterial adhesion inhibition assays form a flexible toolbox for the investigation of bacterial adhesion mechanisms on glycosylated surfaces.

Bacteria use long proteinaceous appendages, called fimbriae or pili, to adhere to the surfaces of their host cells. Widely distributed among the Enterobacteriacae are type 1 fimbriae that mediate mannose-specific bacterial adhesion through the lectin FimH, located at the fimbrial tips. It is possible to design synthetic mannosides such that they show high affinity for FimH and can thus inhibit mannose-specific bacterial adhesion in a competitive manner. It has been found that mannosidic squaric acid monoamides serve especially well as inhibitors of type 1 fimbriae-mediated bacterial adhesion, but it has remained unclear whether this effect is due to specific inhibition of the bacterial lectin FimH or to unspecific bioconjugation between the lectin's carbohydrate binding site and a squaric acid monoamide. A bioconjugation reaction would result in a covalently crosslinked squaric acid diamide. Here it is shown that covalent inhibition of FimH by mannosidic squaric acid derivatives is very unlikely and that compounds of this type serve rather as excellent specific candidates for low-molecular-weight inhibitors of bacterial adhesion. This has been verified by testing the properties of glycosidic squaric acid monoamides in diamide formation, by two different adhesion assays with a series of selected control compounds, and by molecular docking studies that further support the results obtained in the bioassays.

Edited by Renee TsolisKeywords: Bacterial adhesion a-Mannoside inhibitor HT-29 cell Cytotoxicity Anti-adhesion therapy Type 1 fimbriated E. coli a b s t r a c t Bacterial adhesion to glycosylated surfaces is a key issue in human health and disease. Inhibition of bacterial adhesion by suitable carbohydrates could lead to an anti-adhesion therapy as a novel approach against bacterial infections. A selection of five a-mannosides has been evaluated as inhibitors of bacterial adhesion to the polysaccharide mannan, as well as to the surface of live human HT-29 cells. Cell toxicity studies were performed to identify the therapeutic window for a potential in vivo-application of the tested carbohydrates. A previously published mannosidic squaric acid diamide was shown to be exceptionally effective as inhibitor of the bacterial lectin FimH.