A fast and effective alternative to a high-ethanol disinfectant: Low concentrations of fermented ethanol, caprylic acid, and citric acid synergistically eradicate biofilm-embedded methicillin-resistant Staphylococcus aureus

Background: There is a growing need to develop a powerful bactericidal method with low ethanol concentrations due to the frequent ineffectiveness of traditional antibiotics against biofilms and the side effect of a high ethanol concentration. Objectives: This study aims to develop a novel synergistic technique replacing a high-ethanol disinfectant. Methods: Low concentrations of fermented ethanol (FE, 10–20%) with naturally derived antimicrobials, citric acid (CTA, 0.5–1.0%) and caprylic acid (CAP, 0.05–0.15%), were examined against a methicillin-resistant S. aureus (MRSA) biofilm formed on silicone coupons (catheter materials). Results: CTA and CAP were identified as effective antimicrobials that exhibited a synergistic interaction with FE. Complete eradication of MRSA biofilms (>7 log reduction) was obtained within 5 min after treatment with 20% FE plus 1.0% CTA and 0.15% CAP at both 22 and 37 °C, while individual treatments with each material showed negligible bactericidal effects (<1 log reduction except 0.15% CAP treatment at 37 °C). No bacteria were recovered from the surface after the combined treatment (five enrichment tests). The developed compounds were able to disinfect surfaces with more than 5 log-reduction within only 1 min at 22 °C. Confocal microscopy images showed that the combination of all three materials resulted in remarkable membrane damage and cell detachment from the silicone surface. Discusson: Application of FE plus CTA and CAP, therefore, can be a valuable decontamination technique for medical devices or can work as a surface disinfectant, reducing the concerns regarding undesirable high ethanol concentrations in disinfectants.