Chitosan–saccharide conjugates for eradication of Pseudomonas aeruginosa biofilms†

The problem of antibiotic resistance has raised serious concerns globally and hence the development of new materials which can combat these drug-resistant strains has gained a great deal of attention. Herein, we report the use of a biocompatible material, chitosan, as a scaffold to graft saccharides which can specifically target Pseudomonas aeruginosa. We realized this by synthesizing N-functionalized chitosan conjugates by coupling chitosan to fucose and galactose moieties which intercept Pseudomonas aeruginosa lectins and target the bacterial biofilms. A series of six conjugates containing similar proportions of cationic and sugar moieties were synthesized by direct modification of the chitosan backbone using a method that is highly efficient and reproducible. The conjugates showed a bactericidal effect against both Gram positive and Gram negative bacterial strains. An investigation into the antibiofilm activity of the conjugates revealed the optimum combination of the type and positioning of the functionalities that were highly effective in eradicating Pseudomonas aeruginosa biofilms. 2D and 3D imaging of the conjugate-treated biofilms using confocal laser scanning microscopy (CLSM) allowed us to determine that the conjugates not only acted on the surface but also dispersed into deep layers of the biofilm. Interaction between the conjugates and individual bacterial cells in the biofilm was further confirmed by fluorescence labelling of the conjugates and imaging by CLSM.