Chemical Characterization and In vitro Antimicrobial Activity of Caralluma europaea Essential Oil and Its Synergistic Potential with Conventional Antibiotics

Abstract

Aim: This study was carried out to investigate the antioxidant and antimicrobial activities of essential oil from the aerial part of Caralluma europaea and to evaluate the synergistic potential between essential oil and antibiotics. Methodology: The chemical composition, antioxidant, antimicrobial activities and synergetic interaction between antimicrobial agents and essential oil isolated by hydrodistillation from the aerial part of C. europaea were evaluated. The chemical composition was analyzed by a Gas chromatography/mass spectrometry (GC/MS) system. Antioxidant activity was measured employing three methods: scavenging of free radical DPPH, reducing power assay and the inhibition of linoleic acid oxidation. The antimicrobial activity of essential oil against microbial strains was qualitatively and quantitatively assessed by the presence or absence of inhibition zones diameters, and MIC values. The in vitro association between essential oil and some commercial antibiotics was also investigated. Results: The GC/MS analysis shows that a total of 21 constituents were identified and the main compounds were Terpinolene (19.5%), α-Terpinene (16.2%) and Linalool (15.3%). Antioxidant study showed that essential oil exhibited antioxidant activity with IC50 values ranging from 0.32 mg/ml to 1.45 mg/ml. The results of antimicrobial activity showed that the essential oil had an inhibitory effect against the majority of tested microorganisms except K. pneumonia and  P. aeruginosa. Gram-positive bacteria were found to be more sensitive than Gram-negative ones. Furthermore, essential oil approved an interesting antifungal activity against yeast species. Out of 25 combinations tested 64% showed total synergism, 20% had a partial synergistic interaction and 16% showed no effect. The best synergistic effect was obtained with the combination essential oil-gentamycin. Conclusion: Our results are of a great importance and suggest that C. europaea essential oil contain bioactive compounds with antioxidant and antimicrobial properties with possible applications in the food and pharmaceutical industries.