In vitro activity of Propolis on oral microorganisms and biofilms

Natural products are being discussed as alternatives to commonly used chemicals inantimicrobial therapy. The study aimed to investigate the antimicrobial activity of propolis againstmicrobial species associated with caries, periodontal disease, and Candida infections. Two commercially available ethanolic extracts of Brazilian and one of European propolis (EEP) were used. Theminimal inhibitory concentrations (MIC) of propolis and controls against eight microbial strains weredetermined. Scanning and transmission electron microscopy (SEM and TEM) images visualizedthe effect of propolis on microorganisms. Subsequently, the activity on three different multi-speciesbiofilms (both formation and existing biofilms) was assessed. All MIC values of the Brazilian EEPswere low against the tested oral species (<=0.1 mg/mL-3.13 mg/mL propolis (Candida albicans)).The European EEP had slightly higher MICs than the Brazilian EEPs. The SEM and TEM imagessuggest an interaction of propolis with the microbial cell wall. The European EEP exhibited thestrongest effect on retarding biofilm formation, whereas the Brazilian EEPs were highly active againstpreformed biofilms (100 mg/mL propolis of both EEPs reduced colony forming unit counts alwaysby more than 6 log10). The antimicrobial and anti-biofilm activities point to the potential of propolisas an adjunct in oral health care products.