Chemical composition and possible use as adjuvant of the antibiotic therapy of the essential oil of Rosmarinus officinalis L.

Abstract Rosmarinus officinalis L. (rosemary) essential oil (REO) was tested for its antimicrobial activity alone and in combination with conventional antibiotics used against Staphylococcus aureus , Escherichia coli , and Candida strains. The essential oil was chemically described using GC–MS analysis and its antibiotic-resistance modifying activity was assayed using microdilution method. A significant modulatory effect on the drug resistance was verified when the REO was used in association with aminoglycoside antibiotics against E. coli and S. aureus multidrug resistant strains. With respect to the antifungal tested, there was a decrease on amphotericin B activity when this antibiotic was tested in association with the REO against Candida krusei . On the other hand, the combined use of the REO with benzoilmetronidazole was more effective than the antibiotic alone when tested against C. krusei . Rosemary essential oil could become a promising source of metabolites with antibiotic-resistance modifying activity for use against multi-drug-resistant microorganisms.