Novel antimicrobial biomaterials

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Copyright: Rasul, Riaz
Although the widespread use of biomaterials has resulted in significantly improved quality of life and patient survival, biomaterial-associated infections (BAI) remain a vital concern and treatment options are limited. In this study the ability of a novel antimicrobial peptide (AMP) melimine to prevent bacterial colonisation of contact lenses when covalently attached to the material surface was examined against a range of ocular clinical isolates. Various sequences derived from melimine were also analysed to determine if activity comparable to the parent peptide could be achieved with a shorter sequence. The solution mechanism of melimine was studied using circular dichroism and fluorescence spectra in membrane mimetic solvents and the interactions of melimine with bacterial membranes was examined using scanning electron, fluorescence and Atomic force microscopy. Perturbation of membrane integrity was tested by measurement of melimine mediated dye release from bacteria. Additionally, mechanism of action of surface bound melimine and a shorter derivative (melimine 4) was explored. Melimine and melimine 4 covalently-bound to contact lenses effectively reduced adhesion of clinically relevant bacterial species. In solution, melimine assumes a predominantly random coil conformation but when it is solubilised in SDS micelles, which are bacterial membrane mimetic, the -helical content increases to approximately 40%. A major effect of melimine was on the integrity of the cytoplasmic membrane for both P. aeruginosa and S. aureus. However, for P. aeruginosa the rapid loss of cytoplasmic membrane integrity correlated directly with loss of cell viability, while for S. aureus maximal dye release was obtained at concentrations where there was no significant loss of viability. There have been few studies to date investigating differences in the action of cationic peptides towards Gram-positive and Gram-negative bacteria. For covalently-bound peptides displacement of cations on bacterial surfaces and damage to cytoplasmic membrane resulted in loss of cell viability. These results indicate that the melimine and its shorter derivative melimine 4 are excellent candidates for further development as coatings to prevent bacterial colonisation of contact lenses and biomaterials. Further, mechanistic differences between Gram-negative and Gram-positive bacteria may further inform design of novel peptides with improved broad-spectrum activity.
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Rasul, Riaz
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PhD Doctorate
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