Enhanced Antibacterial Efficacy of Cymbopogon winterianus Jowitt in Combination with Carvacrol

The continuous increase of antibiotic resistance and the lag in development of novel antibiotics are two important challenges in treatment of infectious diseases. Essential oils (EOs) and their combinations are promising alternatives for treatment of bacterial infections. Cymbopogon winterianus Jowitt EO, recognized by the European Medicines Agency for its sleep-enhancing and anxiety-relieving properties, also possesses sedative qualities, as noted in the German Commission E monograph, and aids in treating sleep disorders. The aim of the study was to investigate antibacterial activities of the C.winterianus EO and carvacrol combination. Commercial C. winterianus EO and carvacrol were tested for antibacterial activity against the American Type Culture Collection quality control strains Staphylococcus aureus, Enterococcus faecalis, Escherichia coli and Klebsiella pneumoniae using the broth microdilution method. Ciprofloxacin served as the standard antimicrobial agent. Checkerboard assay was used to evaluate the combined effects of C. winterianus EO and carvacrol. The results showed that C. winterianus EO exhibited moderate antibacterial activity against both Gram positive and Gram negative bacteria. The interaction between C. winterianus EO and carvacrol was additive against all tested bacteria. The minimum inhibitory concentration of carvacrol decreased by 2- to 8-fold when the carvacrol combined with C. winterianus EO, and carvacrol also enhanced the antibacterial activity of EO by 2- to 16-fold.