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

Abstract

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 degrees C, while individual treatments with each material showed negligible bactericidal effects (<1 log reduction except 0.15% CAP treatment at 37 degrees 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 degrees 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.