Antimicrobial peptide melimine coating for titanium and its in vivo antibacterial activity in rodent subcutaneous infection models

Implant-associated infections represent a significant health problem and financial burden on healthcare systems. Current strategies for the treatment or prevention of such infections are still inadequate and new strategies are needed in this era of antibiotic resistance. Melimine, a synthetic antimicrobial peptide with broad spectrum activity against bacteria, fungi and protozoa, has been shown to be a promising candidate for development as antimicrobial coating for biomedical devices and implants. In this study, the in vitro and in vivo antimicrobial activity of melimine-coated titanium was tested. The titanium surface was amine-functionalised with 3-aminopropyltriethoxysilane (APTES) followed by reaction with a bifunctional linker 4-(N-maleimidomethyl)cyclohexane-1-carboxylic 3-sulfo-n-hydroxysuccinimide ester (Sulfo-SMCC) to yield a maleimide functionalised surface. Melimine was then tethered to the surface via a thioether linkage through a Michael addition reaction of the cysteine at its N-terminus with the maleimide moiety. Melimine coating significantly reduced in vitro adhesion and biofilm formation of Pseudomonas aeruginosa by up to 62% and Staphylococcus aureus by up to 84% on the titanium substrates compared to the blank (p < 0.05). The activity was maintained after ethylene oxide gas sterilisation. The coating was also challenged in both mouse and rat subcutaneous infection models and was able to reduce the bacterial load by up to 2 log10 compared to the uncoated surface (p < 0.05). Melimine coating is a promising candidate for development as a surface antimicrobial that can withstand industrial sterilisation while showing good biocompatibility.