Terpenes, Antibacterial and Modulatory Antibiotic Activity of Essential Oils from Croton hirtus L’ Hér. (Euphorbiaceae) from Ivory Coast

The chemical composition, antibacterial and modulatory antibiotic activity of essential oils isolated by hydrodistillation from the aerial parts of Croton hirtus (Euphorbiaceae) growing in Ivory Coast, were evaluated. The chemical composition was determined by gas chromatography/mass spectrometry (GC-MS). Essential oil contained 93.49 % of terpene derivatives (15.55 % and 77.94 %) monoterpenes and sesquiterpenes, respectively. Hydrocarbons monoterpenes (14.79 %) were prevalent compared to oxygenated monoterpenes (0.76 %). Moreover among sesquiterpenes, the hydrocarbons species were also detected in a higher percentage (74.06 %) than oxygenated (3.88 %). Three major components found were (E)-caryophyllene (31.75 %), germacrene-D (22.57%) and alpha-humulene (7.42 %). In vitro antibacterial activity was tested using diffusion disk and microdilution methods against Escherichia coli ATCC 29522 and Staphylococcus aureus ATCC 25923. It's modulatory effect combined with antibiotics gentamicin and ceftazidime was also determined. The antibacterial activity was studied by the broth microdilution method. The essential oil from Croton hirtus, were effective only against S. aureus ATCC 25922 (DD = 10.0 +/- 1.0; CMI = 512 mu g/mL). The MICs for gentamicin and ceftazidime, were reduced in the presence of the essential oils against S. aureus ATCC 25922, reduction of 64 to 16 mu g/mL and of 16 to 8 mu g/mL respectively. So, a modulatory effect of Croton hirtus essential oil combined with antibiotics was demonstrated and an important activity against bacterial S. aureus.