Introduction
Over the past two decades, the rise in antimicrobial resistance among pathogenic bacteria has significantly contributed to the persistence of various bacterial infections in the human body (Mah, 2012;Borges et al., 2015). The current research on antimicrobials in the medical field has confirmed the widespread occurrence of antimicrobial resistance, leading to a crisis in antimicrobial resistance (1, 2) . In dentistry, the commonly used local disinfectant chlorhexidine (CHX) not only exhibits toxic effects on host cells but also possesses the ability to promote antimicrobial resistance through mechanisms such as bacterial membrane alteration, resistance genes, and multidrug efflux pumps (3, 4). Another challenge in combating oral biofilms, which are up to 1000 times less susceptible to conventional antimicrobial agents compared to their planktonic counterparts, is the eradication of bacteria residing in the deep layers of these biofilms (5, 6).
In the oral cavity, there are approximately 700 known bacterial species that colonize various surfaces, including the gingiva, teeth, and other oral mucosal sites (7). These bacteria form highly organized microbial communities called biofilms, which provide them with significant protection against antimicrobial agents. The biofilm structure hinders the diffusion of antimicrobial agents (8), and the deepest layers of the biofilm have reduced oxygen levels and a low rate of cell division (9). During the formation of oral biofilms, the initial attachment occurs on the pellicle, a layer primarily composed of salivary proteins. Early colonizers, such as Streptococcus spp., Actinomyces spp.,Veillonella spp., and Neisseria spp., adhere to the pellicle (10, 11). Subsequently, Fusobacterium nucleatum creates a microenvironment with reduced oxygen levels, favoring the adhesion of strict anaerobic pathogens, including late colonizers such asAggregatibacter actinomycetemcomitans , Porphyromonas gingivalis , and Prevotella intermedia (12).
Mediterranean plants have been extensively studied as valuable natural resources for medicinal purposes (13). Over time, numerous biochemical compounds derived from these plants have been identified (14). Further investigations into developing plant-derived antibiotics have highlighted the antimicrobial properties of various compounds, including phenolic acids, flavonoids, plant peptides, phenanthrenes, and terpenes (15-18). Plant metabolites such as phenolics, terpenoids, sulfur-containing compounds, coumarins, quinones, and alkaloids have shown significant biological activity as anti-biofilm agents and inhibitors of quorum sensing (19).
Regional plant products are utilized worldwide, particularly in impoverished nations where they serve as the most affordable form of medicine. However, it is crucial to optimize their formulation and development by targeting specific molecular mechanisms (20). These plant products have the potential to enhance oral health (21) and overall systemic well-being. Several plant-based products have been utilized in oral healthcare and medicinal formulations to combat dental caries, periodontitis, and gingivitis (22). The treatment of pathogenic microbes, which pose significant challenges due to their pathogenicity and resistance, can be improved by targeting them when they are more susceptible to alternative natural antibiotics (23). Considering the complexity of polymicrobial interactions and the intricate compositions of plant-derived products, it is crucial to conduct further research on additional plant species, extraction methods, and explore the synergistic effects of different compounds. Urgent investigation in these areas is necessary.
The objective of this report was to investigate the antimicrobial activity of various Mediterranean herb extracts against different microorganisms. Specifically, the ethyl acetate extracts ofAchillea taygetea , Cistus creticus , Cistus monspeliensis , Lavandula stoechas , Mentha aquatica ,Mentha longifolia , Origanum vulgare , Phlomis cretica , Rosmarinus officinalis , Salvia sclarea ,Satureja parnassica , Satureja thymbra , Sideritis euboea , Sideritis syriaca , Stachys spinosa , andThymus longicaulis were tested against eight common oral pathogenic bacteria and the fungus Candida albicans . Additionally, two reference strains, Staphylococcus aureus andEscherichia coli , which are found on the skin and intestinal mucosa, respectively, were included in the study.
The null hypothesis states that the aforementioned extracts do not exhibit any antimicrobial effects on the tested microbial species. To test this hypothesis, three antimicrobial assays were conducted: the minimal inhibitory concentration (MIC) assay, the minimal bactericidal concentration (MBC) assay, and the biofilm plate assay.