Antimicrobial Surfaces: Stainless Steel Functionalized with the Essential Oil Component Vanillin

Pathogenic microorganisms can adhere to solid surfaces, leading to the formation of biofilms, thus building a physical barrier hindering the penetration and diffusion of antimicrobial compounds. In this context, the use of natural antimicrobial compounds, such as essential oil components, as substitutes for common synthetic antimicrobials in the fight to prevent antimicrobial resistance is explored. As stainless steel is one of the most widely used surfaces in different industries, we have developed an innovative antimicrobial treatment for stainless steel surfaces based on a multi-step functionalization process, in which the stainless steel surface is coated with a silica layer to which a vanillin derivative is covalently attached. The surface was analyzed by microscopy studies, indicating the correct immobilization on the surfaces. Antimicrobial studies (viability and bacterial adhesion assays) were performed against the bacteria Staphylococcus epidermidis, which is one of the most frequent causes of nosocomial infections. The results of the microbiological studies showed that vanillin-functionalized stainless steel surfaces reduce the bacteria viability by 100% and the biofilm formation on the stainless steel surface by 75% compared with non-functionalized surfaces, highlighting the contact-killing and adhesion resistance properties of the developed surface. Additional cycles using the functionalized surfaces showed good maintenance of the antimicrobial coating efficacy. Moreover, the surfaces coated with an intermediate silica layer demonstrated much greater antimicrobial activity than surfaces in which the active molecule was directly functionalized on the stainless steel surface.