In light of the growing antibiotic resistance, the usage of plant-derived antimicrobial agents could serve as an effective alternative treatment against oral infections. This study aimed to investigate the antimicrobial and antibiofilm activity of Mediterranean herb extracts against representative oral microorganisms.

The statement of Hippocrates “Natural forces are the true healers of disease” reflects the fact that thousands of years before any synthetic medicaments were known, nature had been widely considered as the only limitless source of healing components. The ultimate intention has always been to use natural products with favorable antimicrobial, anti-inflammatory and antitumoral properties, without side effects at the chosen concentration, for medicinal purposes. 

Recently, we have therefore seen diverse plant extracts as well as pure natural compounds as part of various treatment protocols in daily medicinal use. Especially plant extracts originating from the Mediterranean area belong to the most frequently screened natural resources for application in medicine 

Extraction procedures

The extraction procedures and the analysis of the obtained extracts were performed under established experimental conditions. The minimum inhibitory (MIC) and bactericidal (MBC) concentrations of the methanol extracts of Cistus creticus ssp. creticus, Cistus monspeliensis, Origanum vulgare, Rosmarinus officinalis, Salvia sclarea and Thymus longicaulis against eight common oral bacteria and the fungus Candida albicans were determined.

Antibacterial activity

The antibiofilm activity against Streptococcus mutans was also quantified using the microtiter plate test. Overall, all tested extracts inhibited, and in concentrations, ≥0.3 mg ml-1 had moderate to high antibiofilm activity comparable to that of chlorhexidine (CHX) against S. mutans. In particular, R. officinalis (MIC: 0.08–5.00 mg ml-1) and S. sclarea (MIC: 0.08–2.50 mg ml-1) showed the highest antibacterial activity, while Cistus spp., R. officinalis and S. sclarea significantly inhibited S. mutans biofilm formation at 0.60, 1.25 and 2.50 mg ml-1, respectively.

Porphyromonas gingivalis and Parvimonas micra were high susceptible to O. Vulgare (MIC = 0.30 mg ml-1), whereas T. longicaulis eradicated all oral bacteria (MBC: 0.15–2.50 mg ml-1). Nevertheless, C. albicans showed no sensitivity to the tested extracts. In conclusion, the tested plant extracts could serve as alternative natural antibacterial and antibiofilm components against oral infections.

This study was supported in part by the German Research Foundation (DFG, AL 1179/2-1). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. There was no additional external funding received for this study. Bettina Spitzmüller is acknowledged for her technical assistance during the biofilm plate assay, while Marie Follo is thanked for the linguistic contribution to this manuscript.