Synergistic antifungal effect of naturally-derived antimicrobials with penetration enhancer against Candida albicans biofilm at 5 °C and 22 °C

Background: Biofilms of fungi such as Candida albicans (C. albicans) can survive even at cold temperatures and are generally difficult to eradicate with well-known antimicrobials. The aim of this study was to develop a novel synergistic technique against C. albicans biofilms using low concentrations of propylene glycol (PG), as a penetration enhancer. It helps naturally-derived antimicrobials [caprylic acid (CA) and carvacrol (CAR)] permeate C. albicans biofilms and cell membranes within short times even in cold environments. Methods: C. albicans biofilms formed on stainless steel coupons were treated with antifungal complexes (PG, CA and CAR at 0.6–1.2 mM) for 1 or 5 min at 5 and 22°C. PG was selected as the highest fungicidal efficacy, as well as its odourless, colourless nature and excellent solubility compared to other penetration enhancers (isopropyl citrate, laurocapram). To visualize cell damage by antifungal complex, treated biofilms at 5°C and 22°C were examined using the confocal microscopy and field emission scanning electron microscopy. Results: Each substance (PG, CA, CAR), when applied alone to C. albicans biofilms for 5 min, showed less than 0.50 log reduction at both 5 and 22°C. C. albicans biofilm was completely eradicated by PG + CA + CAR (all 1.2 mM) after 5 min at 5 and 22°C (> 6.20 log reduction), but treatment mixtures without PG were incompletely eliminated after 1 min at 5°C (1.75 log reduction) and 22°C (3.75 log reduction). Based on the visualization of biofilms, PG + CA + CAR (all 1.2 mM) resulted in remarkable membrane disruption and cell detachment from stainless steel coupons in contrast to the other treatment conditions. Conclusion: This study indicates that trace amounts of developed antifungal complex could be an effective way to inactivate fungal biofilms on the surfaces of the medical and healthcare field even at cold temperatures.