Phytochemical characterization and antibiotic potentiating effects of the essential oil of Aloysia gratissima (Gillies & Hook.) and beta-caryophyllene

The traditional knowledge associated with the use of medicinal plants has significantly contributed to drug development research. In this context, Aloysia gratissima, commonly known as bee-brush or white-brush, has been widely used in Brazilian folk medicine as an analgesic and antimicrobial species. Phytochemical analysis of A. gratissima essential oil has identified sesquiterpene β-caryophyllene (17.3%) as a major component with significant antibacterial activity. Thus, this study aimed to characterize the antibacterial effects of the essential oil obtained from A. gratissima (EOAG) and its major compound β-caryophyllene, as well as to evaluate their potential to act as efflux pumps inhibitors in association with conventional antibiotics. The phytochemical characterization of EOAG was performed by gas chromatography coupled to mass spectrometry (GC-MS), while the antibacterial activity against the strains Pseudomonas aeruginosa 24, Staphylococcus aureus 10, and Escherichia coli 06 was assessed using the broth microdilution method. The antibiotic potentiating activity was investigated by analyzing the ability of the natural products to decrease the minimum inhibitory concentration (MIC) of norfloxacin and ciprofloxacin against S. aureus strains 1199B and K2068. A reduction in the MIC of ethidium bromide in the presence of essential oil components was interpreted as efflux pump inhibition. The GC-MS analysis identified 30 compounds, including β-caryophyllene as the major component. The antibacterial activity analysis demonstrated that both EOAG and β-caryophyllene both EOAG and β-caryophyllene presented antibacterial effects against S. aureus 10 (MIC = 32 μg/mL), in addition to potentiating the activity of norfloxacin against [S. aureus 10], [P. aeruginosa 24], and [E. coli 06]. The isolated compound also reversed the degree of antibiotic resistance observed in strains carrying efflux pumps. In conclusion, the essential oil of A. gratissima and β-caryophyllene have the potential to increase the effectiveness of antibiotics and as such can be used in the development of new therapies against bacterial resistance.