Phytochemical characterization of the Baccharis dracunculifolia DC (Asteraceae) essential oil and antibacterial activity evaluation

The present study had as its objective to evaluate the antibacterial and antibiotic modulatory activity of the Baccharis dracunculifolia (DC) essential oil (EOBD), a species commonly known as “Alecrim do campo”. The essential oil chemical composition analysis and the direct in vitro antibiotic activity evaluation, as well as in combination with the antibiotics Ampicillin, Gentamicin, and Norfloxacin against standard Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 9027, and Staphylococcus aureus ATCC 25923 strains, as well as E. coli 06, P. aeruginosa 24, and S. aureus 10 resistant strains, were performed. Gas chromatography-mass spectrometry (GC–MS) revealed the major terpenoids: Germacrene D (18.4%), (E)-Nerolidol (14.0%), Mustacone (11.2%), Spathulenol (11%), β-pinene (9.5%) and Bicyclogermacrene (8.4%). A direct B. dracunculifolia essential oil antibacterial activity against S. aureus 25923 with a MIC of 102 μg/mL and one of 512 μg/mL against S. aureus 10 were observed. The EOBD synergistically modulated the Norfloxacin antibiotic against P. aeruginosa 24, with a MIC reduction from 50.8 to 6.35 μg/mL, a Gentamicin MIC reduction from 20.16 to 4 μg/mL, and an Ampicillin MIC reduction from 645.1 to 512 μg/mL. The essential oil synergistically modified Norfloxacin activity against E. coli 06 with a MIC reduction from 40.32 to 3.17 μg/mL, and a Gentamicin MIC reduction from 50.8 to 25.4 μg/mL. The essential oil also showed synergism against S. aureus 10 when associated with Norfloxacin, with a MIC reduction from 322.54 to 203.2 μg/mL, whilst when associated with Ampicillin, it demonstrated synergism by reducing the MIC from 80.6 to 20.16 μg/ml. Results from this research revealed that the EOBD is a promising natural product with antimicrobial potential, both directly and in combination with antibiotics, for clinical use against Gram-positive and Gram-negative bacteria.