GC-MS-FID and potentiation of the antibiotic activity of the essential oil of Baccharis reticulata (ruiz & pav.) pers. and α-pinene

•The essential oil of B. reticulata inhibited the multiresistant strain of S. aureus;•This essential oil enhanced the antibiotic activity of norfloxacin and gentamicin;•This synergism was observed on Gram-positive and Gram-negative bacteria;•The anti-bacterial properties of the EOBr is correlated with the α-pinene. The genus Baccharis (Asteraceae) demonstrated the presence of compounds with antibacterial, antifungal and antioxidant activities. Because of the increasing rates of antimicrobial resistance, adequate treatment of infections caused by Gram-negative bacteria has become challenging. The objective of the present study was evaluate the antibacterial and antibiotic-modifying activity of the essential oil obtained from Baccharis reticulata (Ruiz & Pav.) Pers. and the compound α-pinene against Pseudomonas aeruginosa and other multiresistant bacteria. An analysis by gas chromatography associated with mass spectrometry (GC/MS) revealed the presence of dilapiol (33.8 %), α-pinene (31.7 %) and β-pinene (9.4 %) as major components of the oil. The determination of the Minimum Inhibitory Concentration (MIC) revealed that the oil has antibacterial activity against S. aureus only. However, the oil potentiated the norfloxacin and gentamicin against all strains evaluated. Also, α-pinene increased the activity of norfloxacin against E. coli, as well as potentiated the activity of norfloxacin and gentamicin against S. aureus. Therefore, the authors conclude that the essential oil of B. reticulata, as well as the compound α-pinene, have antibacterial and antibiotic-modulating activities that make them useful in the development of new weapons against bacterial resistance.