BackgroundConsidering that antimicrobial resistance among oral pathogens is a significant concern in dental practice, with broader implications for overall health due to the oral microbiota serving as a reservoir for antibiotic resistance genes (ARGs), research into natural products is crucial for addressing this issue. ObjectiveThis study aimed to evaluate tea tree oil (TTO) and chitosan (CH) performance against oral pathogens, including mixed-species biofilm, and its effects on bacteria growth, in addition to chemical characterization and cytotoxicity of TTO. MethodsTea Tree Oil and low molecular weight chitosan were used in this study. The chemical composition of TTO was analyzed using gas chromatography coupled with mass spectrometry (GC-MS). To evaluate TTO's antimicrobial properties, time-kill and cell viability assays were conducted. Additionally, minimum inhibitory concentration (MIC), minimum microbiocidal concentration (MMC), checkerboard, and biofilm assays were performed using TTO and CH alone and in combination. ResultsTTO chromatography peaks found consistent with the standard ISO4730:2017 and literature. TTO and CH exhibited inhibitory activity against all tested microorganisms. The predominantly microbiostatic activity of TTO is probably related to terpinen-4-ol associated with terpinene. The oil at MIC value was able to delay the log phase of Aggregatibacter actinomycetemcomitans growth. Fibroblasts (L929) viability remained above 70 % during 24 h for TTO concentrations ranging from 0.5 to 0.0625 mg/ml. TTO-CH combination showed a synergistic activity (FIC = 0.5) against A. actinomycetemcomitans and Streptococcus sanguinis, at a concentration of 0,25MIC for both species. The compounds at MIC concentration inhibited both monospecies and mixed-species biofilms studied bacteria to the same extent as the azithromycin control. ConclusionTTO and CH demonstrated efficacy in combating oral pathogens and TTO-CH combination offers a promising approach to confront microbial resistance in the oral environment.
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