Formulation, physicochemical characterization, and antimicrobial evaluation of drug-loaded essential oil microemulsions against Methicillin-resistant Staphylococcus aureus -associated diabetic foot ulcer infections

Abstract

Diabetes Mellitus, a leading endocrine disorder characterized by persistent hyperglycemia, ischemia, and neuropathy, causes ulcerative wounds that are often colonized by multidrug-resistant pathogens, such as Methicillin-resistant Staphylococcus aureus (MRSA), which exacerbate wound infections and can lead to complications such as sepsis and necrosis in Diabetic Foot Ulcers (DFU). This study aims to formulate phytochemical-based nanovesicle carriers for potential wound-healing applications to retain the therapeutic effects of antimicrobial compounds with their localized delivery. This investigation develops microemulsions containing Eugenol, Clove, and Cinnamon oils to encapsulate Vancomycin and Methicillin, preserving their antibacterial activity while providing sustained delivery to the site of action. Microemulsions tested for thermodynamic stability, DLS, zeta potential, pH, FTIR, and TEM, showed optimal hydrodynamic size and PDI (within 30 nm and 0.5), a more negative zeta potential of around −19 mV, and an acidic pH. FTIR of blank emulsions against drug modifications confirmed successful drug incorporation, and TEM showed spherical-oval morphology. Antimicrobial testing using AST, MIC, Antibiofilm, Checkerboard, and Time-kill assays showed that drug-loaded emulsions provided measurable in vitro antibacterial activity against the tested clinical MRSA isolates, with activity varying by formulation and isolate (Eug-Van in MRSA-CI 1 and Clo-Van in MRSA-CI 2). Meanwhile, for Methicillin formulations, Clo-Met showed measurable inhibition against both tested isolates. Release kinetics revealed that drug-loaded emulsions showed sustained, diffusion-controlled release of the active therapeutics – Vancomycin and Methicillin over 24 h, with slowly increasing concentrations initially, followed by a plateau with maximum release in the case of Eug-Van microemulsion. These results demonstrate the considerable potential of these drug-loaded microemulsions as advanced nanocarrier systems for localized antimicrobial delivery in MRSA-colonized DFU infections.