Antibacterial and modifying-antibiotic activities of the essential oils of Ocimum gratissimum L. and Plectranthus amboinicus L

Introduction Developing resistance to antimicrobial agents is increasingly observed for many microorganisms is increasingly becoming a problem worldwide. The aim of the present work was to evaluate the antibacterial and antibiotic-modifying activity of essential oils of Ocimum gratissimum and Plectranthus amboinicus (Lamiaceae), alone and combined. Methods Standard and multiresistant bacterial strains of Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa were utilized, and antibiotics of the aminoglycoside class were tested, using the microdilution technique. Results The antibacterial effect of the O. gratissimum L. and P. amboinicus L. oils alone and combined have a minimum inhibitory concentration (MIC) ≥ 1024 μg/mL, except against E. coli ATCC10536, which showed a MIC = 128 μg/mL and against S. aureus ATCC25923 with MIC = 512 μg/mL. The drug-modifying effect of the essential oil of O. gratissimum L. resulted in an antagonism, reducing the effect of antibiotics, against all bacterial strains assayed. However, the essential oil of P. amboinicus L. showed a synergistic effect, potentiating the antibiotic activity of these drugs against the bacterial strains assayed. When the mixture of the O. gratissimum and P. amboinicus oils was combined with the antibiotic, a synergistic effect was observed. Conclusions The data obtained are promising, but further studies are needed to isolate the active compounds and to conduct pharmacological tests in vivo, making it possible to develop new therapeutic alternatives for the treatment of diseases caused by multiresistant microorganisms.