Nanoemulsions of Canarium schweinfurthii sap and Dacryodes edulis kernel essential oils: Chemical profile and in vitro efficacy against diarrheagenic bacteria

Background: The objective of this study was to evaluate the in vitro antibacterial activity of nanoemulsions based on the essential oils of Canarium schweinfurthii and Dacryodes edulis against enteric bacteria responsible for diarrhea. Methods: The essential oils were extracted by the hydrodistillation method using a Clevenger-type apparatus, and the chemical composition was determined by gas chromatography with flame ionization detection (GC-FID) and gas chromatography (GC) coupled with mass spectrometry (GC/MS). Nanoemulsions were prepared, and their antibacterial activity was evaluated using the disc diffusion method and by the micro-dilution method in liquid medium, at the end of which the inhibitory diameters and minimum inhibitory concentrations (MICs) were obtained with respect to the different isolates. Results: C. schweinfurthii showed 3.96%, and D. edulis showed 0.10% extraction yield with 19 and 20 compounds found, respectively. The chemical profile of C. schweinfurthii was composed mainly of α -pinene (40.92%), myrcene (16.02%), and β-phellandrene (12.73%); whereas that of D. edulis was majorly composed of limonene (35.52%), α-terpineol (30.72%), and p-cymene (8.82%). Both nanoemulsions showed a good antibacterial activity: C. schweinfurthii MICs were found to be between 312.5 µg/mL (Salmonella Typhi) and 5000 µg/mL (E. coli and E. aerogenes), with a bactericidal effect on most strains and a bacteriostatic effect on S. Typhi. In the case of D. edulis, the MICs were 625 µg/mL to 5000 µg/mL with bactericidal activity against E. aerogenes and E. coli. Conclusion: Although these nanoemulsions were less active than the reference ciprofloxacin, they could retain the biological activities of the essential oils, making them promising plant-based substitutes to treat enteric infections by diarrheagenic bacteria.