Chemical Profiling, Antibacterial Efficacy, and Synergistic Actions of Ptychotis verticillata Duby Essential Oil in Combination with Conventional Antibiotics

Introduction: The primary aim of the current investigation is to assess the chemical composition and antibacterial efficacy of Ptychotis verticillata essential oil (PVEO) against three Gram-positive bacteria (Staphylococcus aureus, Micrococcus luteus, and Bacillus subtilis) and three Gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa, and Klebsiella pneumoniae). Furthermore, this research endeavors to investigate the potential synergistic effects of PVEO when combined with established antibiotics (Amoxicillin, Erythromycin, and Ampicillin), with a focus on discerning their interaction dynamics. Methods: The phytochemical profiling of PVEO was performed via the Gas Chromatography-Mass Spectrometry technique. The broth dilution test determined the interaction effect between PVEO and these three antibiotics. Results: Components γ-terpinene (38.96%), p-cymene (19.38%), thymol (18.07%), and carvacrol (6.99%) are the major bioactive moleculs composing this studied essential oil. PVEO demonstrated significant antibacterial activity with minimum inhibitory concentration (MIC) values ranging from 0.2 against E coli to 2 mg/mL against M luteus. The assessment of the synergistic activity between PVEO and antibiotics was accomplished through the utilization of the Fractional Inhibitory Concentration Index (FICI). The combination of PVEO and amoxicillin against M luteus demonstrated the best synergistic action with a FICI value of 0.43. Conclusion: Significant reductions, ranging from two to sevenfold, in the MIC values of PVEO, and antibiotics were observed. This noteworthy synergistic interaction between highly potent essential oils and synthetic antibiotics holds the potential to open avenues for novel combination therapies aimed at addressing infections caused by multiresistant microorganisms, even at notably reduced concentrations within the pharmaceutical sector.