Coriander essential oil and linalool - interactions with antibiotics against Gram-positive and Gram-negative bacteria

The aim of this study was to evaluate the antibacterial activity of coriander essential oil and its major constituent, linalool, in combination with antibiotics against Gram-positive (methicillin-susceptible and methicillin-resistant Staphylococcus aureus, S. epidermidis) and Gram-negative bacteria (Pseudomonas aeruginosa, Escherichia coli). The chemical composition of coriander essential oil was analyzed by gas chromatography with flame ionization and mass spectrometry detection. The antibacterial activity of coriander essential oil, linalool and their combinations with antibiotics were assessed by the broth microdilution and checkerboard assays respectively. Thirty-four compounds were identified in coriander essential oil, linalool (70·11%) being predominant. Coriander essential oil and linalool showed synergistic interactions with antibiotics (oxacillin, amoxicillin, gentamicin, ciprofloxacin, tetracycline) against both Gram-positive and Gram-negative bacteria. In these synergistic combinations, minimum inhibitory concentrations of antibiotics were markedly reduced; even antibiotic resistance reversal activity was recorded. These findings are very promising for the development of new therapeutic options for bacterial infections. SIGNIFICANCE AND IMPACT OF THE STUDY: Methicillin-resistant Staphylococcus aureus (MRSA) and Gram-negative bacteria are still major threats to human health and, therefore, identification of new antibacterial agents or combinations with high potency is needed. Our study found synergistic interactions between coriander essential oil/linalool and antibiotics against MRSA and other Gram-positive bacteria (methicillin-susceptible S. aureus, S. epidermidis), but also Gram-negative bacteria (Pseudomonas aeruginosa, Escherichia coli). Increase in antibiotic susceptibility and reversal of antibiotic resistance were also demonstrated. Combinations of coriander essential oil/linalool and antibiotics are thus very promising for the development of novel antibacterials.