Insights into betulinic acid as a promising molecule to fight the interkingdom biofilm Staphylococcus aureus-Candida albicans

The demand for antibiofilm molecules has increased over several years due to their potential to fight biofilm-associated infections, such as those including the interkingdom Staphylococcus aureus-Candida albicans occurring in clinical settings worldwide. Recently, we identified a pentacyclic triterpenoid compound, betulinic acid, from invasive macrophytes, with interesting antibiofilm properties. The aim of the present study was to provide insights into the mechanism of action of betulinic acid against the clinically relevant bi-species S. aureus-C. albicans biofilms. Microscopy examinations, flow cytometry and crystal violet assays confirmed that betulinic acid was effective at damaging mature S. aureus-C. albicans biofilms or inhibiting their formation, reducing biofilm biomass by 70% on average and without microbicidal activity. The results suggested an action of betulinic acid on cell membranes, inducing changes in properties such as composition, hydrophobicity and fluidity as observed in C. albicans, which may hinder the early adhesion step, biofilm growth and the physical interactions of both microbial species. Further results of real-time polymerase chain reaction argued in favour of a reduction in S. aureus-C. albicans physical interaction due to betulinic acid by the modulation of biofilm-related gene expression, as observed in early stages of biofilm formation. This study revealed the potential of betulinic acid as a candidate agent for the prevention and treatment of S. aureus-C. albicans biofilm-related infections.