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Background: Aloysia gratissima (Verbenaceae), popularly known as bee-brush or whitebrush, has been widely used in Brazilian folk medicine as analgesic, expectorant and antimicrobial. Phytochemical studies have identified β-caryophyllene as one of the major components of the essential oil of this plant. This bioactive sesquiterpene has been shown to have anti-inflammatory and antibacterial activities. Purpose: The present study aimed to characterize the chemical profile and evaluate the antibacterial and antibiotic-enhancing activities of the essential oil obtained from Aloysia gratíssima (EOAG) and β-caryophyllene. Methods: The phytochemical analysis was performed by gas chromatography coupled to mass spectrometry (GC-MS). The antibacterial activity against Pseudomonas aeruginosa 24, Staphylococcus aureus 10, and Escherichia coli 06 was assessed by determining the minimum inhibitory concentration (MIC) using the broth microdilution method. The potentiation of the antibiotic activity by the EOAG and the β-caryophyllene was performed using the MIC evaluation of the antibiotic alone or in association with the essential oil and its main compound. To evaluate the minimum reduction of the drug concentration necessary, the Dose Reduction Index (DRI) was calculated. Results: A reduction in the MIC of the antibiotics against strains treated simultaneously with the essential oil or β-caryophyllene was observed. The GC-MS analysis of the EOAG identified 30 compounds, including β-caryophyllene as the major component. Both OEAG and β-caryophyllene presented antibacterial activity against S. aureus, in addition to potentiating the action of norfloxacin against S. aureus, P. aeruginosa, and E. coli. Conclusions: These substances also reversed the antibiotic resistance to gentamicin and erythromycin against of S. aureus and P. aeruginosa, respectively.

Considering the evidence that essential oils, as well as safrole, could modulate bacterial growth in different resistant strains, this study aims to characterize the phytochemical profile and evaluate the antibacterial and antibiotic-modulating properties of the essential oil Ocotea odorífera (EOOO) and safrole against efflux pump (EP)-carrying strains. The EOOO was extracted by hydrodistillation, and the phytochemical analysis was performed by gas chromatography coupled to mass spectrometry (GC-MS). The antibacterial and antibiotic-modulating activities of the EOOO and safrole against resistant strains of Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa were analyzed through the broth microdilution method. The EP-inhibiting potential of safrole in association with ethidium bromide or antibiotics was evaluated using the S. aureus 1199B and K2068 strains, which carry genes encoding efflux proteins associated with antibiotic resistance to norfloxacin and ciprofloxacin, respectively. A reduction in the MIC of ethidium bromide or antibiotics was used as a parameter of EP inhibition. The phytochemical analysis identified 16 different compounds in the EOOO including safrole as the principal constituent. While the EOOO and safrole exerted clinically relevant antibacterial effects against S. aureus only, they potentiated the antibacterial activity of norfloxacin against all strains evaluated by our study. The ethidium bromide and antibiotic assays using the strains of S. aureus SA1119B and K2068, as well as molecular docking analysis, indicated that safrole inhibits the NorA and MepA efflux pumps in S. aureus. In conclusion, Ocotea odorifera and safrole presented promising antibacterial and antibiotic-enhancing properties, which should be explored in the development of drugs to combat antibacterial resistance, especially in strains bearing genes encoding efflux proteins.