Antibiofilm Potential of Plant Extracts: Inhibiting Oral Microorganisms and Streptococcus mutans

Nomi Bartels ¹ Aikaterini Argyropoulou ² Ali Al-Ahmad ³ Elmar Hellwig ³ Leandros Alexios Skaltsounis ² Annette.wittmer@uniklinik-freiburg.de Wittmer ³ Kirstin Vach ³ Lamprini Karygianni ^4*

• ¹ Department of Prosthodontics, Faculty of Medicine Carl Gustav Carus, TU Dresden, Dresden, Germany
• ² Faculty of Pharmacy, National and Kapodistrian University of Athens, Athens, Greece
• ³ Faculty of Medicine, University of Freiburg, Freiburg, Germany
• ⁴ Center of Dental Medicine, Faculty of Medicine, University of Zurich, Zürich, Zürich, Switzerland

A range of disinfectant mouthwashes are available for oral hygiene. The gold standard is Chlorhexidine digluconate (CHX), which, like other available products, cannot be used without side effects in the long term. However, in recent years, therapy with herbal products, often considered antiquated, has regained considerable interest. Therefore, the search for plant compounds as an alternative to existing oral disinfectants is meaningful. In this study, eleven Mediterranean plant extracts were tested for their antimicrobial effect in vitro. Methanol extracts of the following plants were produced by the pharmaceutical faculty of the University of Athens: Mentha aquatica, Mentha longifolia, Sideritis euboea, Sideritis syriaca, Stachys spinosa, Satureja parnassica, Satureja thymbra, Lavandula stoechas, Achillea taygetea, Phlomis cretica, and Vaccinium myrtillus. The extracts were dissolved for microdilution experiments at concentrations ranging from 10 mg/ml to 0.019 mg/ml. The oral pathogens tested were Streptococcus mutans, Streptococcus oralis, Streptococcus sobrinus, Prevotella intermedia, Fusobacterium nucleatum, Parvimonas micra, Porphyromonas gingivalis, and Candida albicans. Enterococcus faecalis, Staphylococcus aureus, and Escherichia coli were used as references.All extracts, except the methanol extract of V. myrtillus, showed an antibacterial effect at concentrations ranging from 10 mg/ml to 0.15 mg/ml. None of the extracts exhibited a significant antifungal effect. In general, the anaerobic pathogens could be inhibited and killed at lower concentrations compared to the aerobic pathogens. S. oralis also showed good susceptibility to the extracts. Additionally, the extracts' ability to inhibit biofilm formation by S. mutans was tested. L. stoechas at a concentration of 0.3 mg/ml showed a moderate inhibitory effect. The extracts of L. stoechas, S. thymbra, S. parnassica, and the methanol extract of V. myrtillus were effective at concentrations up to 1.25 mg/ml. P. cretica was able to inhibit and kill S. mutans at a concentration of 0.6 mg/ml, but its effectiveness in biofilm inhibition significantly decreased at 2.5 mg/ml. The study's hypothesis that all extracts would exhibit an antimicrobial effect was thus confirmed.