Chemical composition, antioxidant and evidence antimicrobial synergistic effects of Periploca laevigata essential oil with conventional antibiotics

Medicinal plants constitute a potential reservoir of several effective antioxidant and antimicrobial agents especially in developing countries were resources are lacking. Compounds of natural origin are more effective, safer and have less side effects. For continuing research on biological properties of Moroccan medicinal plants and identification of new natural antioxidant and antimicrobial agents, the present study was conducted to investigate the chemical composition, antioxidant and antimicrobial effect of the association between some conventional antibiotics and Periploca laevigata essential oil obtained by hydro-distillation. The chemical composition was analyzed by a gas chromatography/mass spectrometry (GC/MS) system and a total of 22 compounds were identified. n-hexadecanoic acid (14.6%) and 4,4,7a-Trimethyl-5,6,7,7a-tetrahydro-4H-benzofuran-2-one (11.8%) were found to be the main constituents. A moderate antioxidant activity was found as evaluated by 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical method, reducing power and ß-carotene-linoleic acid assays with IC50 values ranging from 0.69 to 2.86 mg/ml. The antimicrobial investigation showed an inhibitory effect against seven and four respectively tested bacterial and fungal species. In general, Gram positive bacteria (S. aureus, M. luteus, B. cereus and B. subtilis) were found to be more sensitive than Gram-negative ones. The antifungal activities showed that C. albicans was the most susceptible. The association between conventional antibiotics (cefexime, ciprofloxacin, gentamicin and fluconazole) and the essential oil showed a high synergistic effect. Combination with gentamicin exhibited interesting synergistic effect against both Gram-positive and Gram-negative bacteria with lowest FIC index values (0.28-0.50), followed by essential oil-ciprofloxacin which is especially active against Gram-positive bacteria (FICi = 0.31-0.38).Whereas, the association essential oil-fluconazole showed a total synergistic effect (FICi = 0.25-0.37) for yeasts except C. albicans. The results showed that the essential oil possesses compounds with antimicrobial and antioxidant properties and a good synergistic effect in association with antibiotics. The present study suggests that the essential oil can be considered as new and potential source of natural antioxidant and antimicrobial agents.