GC-MS Profiling and Antimicrobial Activity of Eight Essential Oils Against Opportunistic Pathogens with Biofilm-Forming Potential

Essential oils (EOs) are complex plant-derived products known for their broad-spectrum antibacterial activity. This study aims to evaluate the chemical composition of eight essential oils-EOs (Caryophylli aetheroleum, Menthae aetheroleum, Origani aetheroleum, Rosmarini aetheroleum, Salviae aetheroleum, Melaleucae aetheroleum, Limonis aetheroleum, and Curcumae aetheroleum) and to evaluate their antibacterial and antibiofilm activity against five opportunistic pathogens with biofilm-forming potential (methicillin-susceptible and methicillin-resistant <i>Staphylococcus aureus</i>, <i>Pseudomonas aeruginosa</i>, <i>Enterococcus faecalis</i>, <i>Escherichia coli</i>, and <i>Klebsiella pneumoniae</i>). GC-MS was used to determine the chemical composition of the EOs, and antibacterial activity was evaluated using broth microdilution to determine the minimum inhibitory concentration and minimum bactericidal concentration. Biofilm inhibition was assessed by a crystal violet assay. Oxygenated monoterpenes and phenolic compounds were dominant in Origani, Menthae, Rosmarinus, Melaleucae, and Caryophylli aetheroleum. Potent inhibitory effects against the tested bacterial strains were observed for clove, tea tree, oregano, and rosemary EOs. The antimicrobial efficacy of EOs is closely linked to their chemical composition. Tea tree and oregano EOs exhibited the broadest spectrum of antimicrobial activity, while peppermint and curcuma oils were the least potent. Cytotoxicity thresholds from the literature suggest that some effective EO concentrations exceed safe mucosal limits, particularly in continuous high-dose applications, but short-contact delivery systems or adjunctive use with different agents may mitigate safety concerns. These findings support further investigation into their therapeutic applications in oral health products.