The aim of this study was to evaluate the interference of essential oils from Lippia sidoides Cham, Plectranthus amboinicus Lour Spr., Conyza bonariensis L. and Eucalyptus citriodora Hook on the antibacterial effect of clinically used antibiotics. The assays were carried out with ampicillin (10 µg/mL), cephalotin (30 µg/mL), chloraphenicol (30 µg/mL), gentamicin (10 µg/mL) and tetracyclin (30 µg/mL) isolated and associated with essential oils (4% v/v) by the solid medium diffusion procedure using filter paper discs. The results showed interference of some essential oils on the antibacterial activity of the assayed antibiotics. It was observed the development of growth inhibition halo with different diameters when the antibiotics were applied alone and associated with essential oils. Synergic or antagonic behavior was more prominent in interactions with S. aureus and S. epidermidis strains. On the other hand, it was observed a smaller interference of essential oils on the effect of the antibiotics against Gram negative strains, mainly P. aeruginosa. These results show that the use of plants by-products could some times interfere on the effectiveness of antibiotics used clinically.
Medicinal plants; essential oils; antibiotics; associated use; interference
