Chemical composition and antimicrobial activity of leaf and bark essential oils of Apodocephala pauciflora Baker (Asteraceae)

The present work aims to study the chemical composition and the antimicrobial and toxicological properties of the essential oils (EOs) of Apodocephala pauciflora leaves (LEO) and stem bark (BEO). LEO and BEO were extracted from fresh material by hydrodistillation with a yield of 0.1%. They are light, light yellow, strong smelling and dextrorotatory. Gas chromatography/mass spectrometry (GC/MS) analysis identified 42 components in LEO and 38 in BEO representing 97.54% and 99.44% of the overall composition respectively. In LEO, the major components were α-pinene (27.5%), sabinene (13.62%) and β-pinene (12.0%) and in BEO, α-pinene (34.32%), myrcene (15.1%), sabinene (14.53%). Main components such β-pinene, phellandrene and limonene were common to LEO and BEO but at different rates. However, some components were not common to both EOs: for example, cubenol (5.07%) in LEO was absent in BEO and vice versa humulene (3.91%) in BEO was absent in LEO. Both EOs were effective against all microorganisms tested, including Gram (+) and Gram (-) bacteria and a fungus, with a strain-dependent intensity. BEO was more efficient than LEO. Streptococcus pneumoniae, Pseudomonas aeruginosa, Vibrio fischeri and Candida albicans were the most susceptible. LEO was bacteriostatic against Clostridium perfringens and Candida albicans but bactericidal against the other germs tested, whereas BEO was bactericidal against all germs. With LD50 of 2.48 and 2.34 g/kg body weight, LEO and BEO were slightly toxic to mice by oral route. LEO and BEO could be used as alternatives to synthetic antibiotics against several pathogenic microorganisms.