Nature is an unexplored reservoir of novel phytopharmaceuticals. Since biofilm-related oral diseases often correlate with antibiotic resistance, plant-derived antimicrobial agents could enhance existing treatment options. Therefore, the rationale of the present report was to examine the antimicrobial impact of Mediterranean natural extracts on oral microorganisms. Five different extracts from Olea europaea, mastic gum, and Inula viscosa were tested against ten bacteria and one Candida albicans strain. The extraction protocols were conducted according to established experimental procedures. Two antimicrobial assays—the minimum inhibitory concentration (MIC) assay and the minimum bactericidal concentration (MBC) assay—were applied. The screened extracts were found to be active against each of the tested microorganisms. O. europaea presented MIC and MBC ranges of 0.07–10.00 mg mL−1 and 0.60–10.00 mg mL−1, respectively. The mean MBC values for mastic gum and I. viscosa were 0.07–10.00 mg mL−1 and 0.15–10.00 mg mL−1, respectively. Extracts were less effective against C. albicans and exerted bactericidal effects at a concentration range of 0.07–5.00 mg mL−1 on strict anaerobic bacteria (Porphyromonas gingivalis, Prevotella intermedia, Fusobacterium nucleatum, and Parvimonas micra). Ethyl acetate I. viscosa extract and total mastic extract showed considerable antimicrobial activity against oral microorganisms and could therefore be considered as alternative natural anti-infectious agents.

Background In view of the increasing antibiotic resistance, the introduction of natural anti-infective agents has brought a new era in the treatment of bacterially derived oral diseases. Methods The aim of this study was to investigate the antimicrobial potential of five natural constituents of Olea europaea (oleuropein, maslinic acid, hydroxytyrosol, oleocanthal, oleacein) and three compounds of Pistacia lentiscus (24Z-isomasticadienolic acid, oleanolic acid, oleanonic aldehyde) against ten representative oral bacterial species and a Candida albicans strain. After the isolation and quality control of natural compounds, the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) assay were performed. Results Among all O. europaea -derived constituents, maslinic acid was the most active (MIC = 4.9–312 μg mL − 1 , MBC = 9.8–25 μg mL − 1 ) one against oral streptococci and anaerobic pathogenic bacteria ( Porphyromonas gingivalis , Fusobacterium nucleatum , Parvimonas micra ), while oleuropein, hydroxytyrosol, oleocanthal and oleacein showed milder, yet significant effects against P. gingivalis and F. nucleatum . Among all P. lentiscus compounds, oleanolic acid was the most effective one against almost all microorganisms with MIC values ranging from 9.8 μg mL − 1 ( P. gingivalis ) to 625 μg mL − 1 ( F. nucleatum , P. micra ). In the presence of 24Z-isomasticadienolic acid, a mean inhibitory concentration range of 2.4 μg mL − 1 to 625 μg mL − 1 was observed for strict anaerobia. The MIC value for 24Z-isomasticadienolic acid was estimated between 39 μg mL − 1 ( Streptococcus sobrinus , Streptococcus oralis ) and 78 μg mL − 1 ( Streptococcus mutans ). All tested compounds showed no effects against Prevotella intermedia. Conclusions Overall, maslinic acid and oleanolic acid exerted the most significant inhibitory activity against the tested oral pathogens, especially streptococci and anaerobic oral microorganisms.