In vitro antimicrobial activity of chlorhexidine in combination with essential oils of Mentha x piperita L. & Thymus serpyllum L. & Pelargonium graveolens L’hér

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In this study, the antimicrobial potential of Mentha piperita & Thymus serpyllum &Pelargonium graveolens essential oil combinations was evaluated with Chlorhexidine. These species used ethnobotanically against throat infections. The commercial oils were analysed by GC-MS to confirm phytochemistry. Antimicrobial evaluation of the essential oils against Staphylococcus aureus and Streptococcus mutans were performed using in vitro microdilution assay. Binary combinations of Chlorhexidine-essential oils were evaluated using the checkerboard method. M. piperita essential oil contained 47% menthol as the major component, whereas the main component of T. serpyllum essential oil was 19% geraniol, and the main component of P. graveolens was 25% citronellol, respectively. The calculated fractional inhibition concentration index (FICI) of chlorhexidine-T. serpyllum combinations against S. mutans resulted as antagonistic (FICI 3.3643), while the FICI of chlorhexidine-P. graveolens essential oil combination resulted in synergistic (FICI 0.4326). Also, the FICI value = 0.252 of chlorhexidine-P. graveolens essential oil combinations against S. aureus were synergistic. To the best of our knowledge, combinations of these oils with Chlorhexidine were observed for the first time in this study with the potential application as mouthwash formulation.