Comparative antimicrobial potential of Ocimum basilicum essential oil, estragole and estragole/β-cyclodextrin complex in an infection model on adult zebrafish

Background: The need of the growth the production of more efficient medications for the control of bacterial infections has waked up the pharmaceutical industry to develop new drugs from compounds isolated from plants. Purpose: Therefore, the aim of the present study is to investigate the antimicrobial potential of the essential oil of Ocimum basilicum (OEFOb) leaves, of its main compound estragole (ES) and its estragole/β-cyclodextrin complex (ES/β-CD) on adult zebrafish (aZF). Methods: The ES was purchased from Sigma Aldrich (Brazil). The antimicrobial activity was evaluated by the broth microdilution method, determining the minimum inhibitory concentration (MIC) and assessing the potentiating effect in vitro, by the adapted method of in vivo infection by S. aureus and E. coli in aZF, and by the adapted method of potentiation of antibiotic action on aZF. Results: The OEFOb showed MIC values of 2048 μg/mL against the strains in the in vitro assay, on the other hand, estragole and its ES/β-CD complex both showed MIC values of 1024 μg/mL. The in vivo model of infection by Staphylococcus aureus and Escherichia coli on aZF was established during the period of 24 and 48h after infection by bacterial inoculum. The oral administration of the OEFOb, ES, and ES/β-CD complex did not cause mortality in the aZF up to 48h of the test, as well as reduced the infection induced by strains S.a. ATCC 25923, S.a. 10, E.c. ATCC 2592 and E.c. 06 in the aZF, demonstrating clinically relevant effects. In verifying the synergistic effect, the OEFOb, ES, and ES/β-CD complex was significant against the strains studied, with the ES/β-CD complex presenting more relevant results when associated with gentamicin. Conclusions: The OEFOb, ES, and ES/β-CD showed relevant antibacterial activity, as well as a synergistic effect in combination with gentamicin against strains of S. aureus and E. coli in the in vitro assay. It was possible to establish the model of in vivo infection by strains of S. aureus and E. coli on aZF during the period of 24 and 48h, by bacterial inoculum. P1 (OEFOb), P2 (ES), and P3 (ES/β-CD) demonstrated clinically relevant effects by inhibiting the infection induced by the pathogens in the aZF, and when associated with gentamicin, they were significant against the strains of S. aureus and E. coli, with the ES/β-CD complex being the most relevant in the association with the antibiotic.