Synergistic effect of Thymbra spicata L. extracts with antibiotics against multidrug- resistant Staphylococcus aureus and Klebsiella pneumoniae strains

OBJECTIVES To evaluate the in vitro interaction between different extracts of Thymbra spicata L. and certain antimicrobial drugs of different mechanisms, including ampicillin, cefotaxime, amikacin and ciprofloxacin. This study was performed against multidrug-resistant strains of Staphylococcus aureus and Klebsiella pneumoniae. MATERIALS AND METHODS Evaluation of antibacterial activity and synergy interaction between plant extracts and antimicrobial agents was carried out using checkerboard microdilution. RESULTS Different interactions (synergistic, additive and indifference) were observed between plant crude extracts and used antibiotics depending on the strain. The fractional inhibitory concentration (FIC) index ranged from 0.02 to 1.5 for S. aureus and 0.25 to 2 for K. pneumoniae strains. The best synergistic capacity appeared with cefotaxime against S. aureus strains, where the activity of cefotaxime was increased from 8- to 128-fold. CONCLUSION These results may indicate that T. spicata extracts potentiates the antimicrobial action of antibiotics, suggesting a possible utilization of this herb in combination therapy against emerging multidrug-resistance S. aureus and K. pneumoniae.