Aims: Due to the emergence of multi-drug resistance, alternatives to conventional
antimicrobial therapy are needed. This study aims to investigate the
in vitro pharmacological interactions between essential oils (considered valuable
as natural therapeutic treatments) and conventional antimicrobials (ciprofloxacin
⁄ amphotericin B) when used in combination.
Methods and Results: Interactions of the essential oils (Melaleuca alternifolia,
Thymus vulgaris, Mentha piperita and Rosmarinus officinalis) when combined
with ciprofloxacin against Staphylococcus aureus indicate mainly antagonistic
profiles. When tested against Klebsiella pneumoniae the isobolograms show
antagonistic, synergistic and additive interactions depending on the combined
ratio. The R. officinalis ⁄ ciprofloxacin combination against K. pneumoniae displayed
the most favourable synergistic pattern. The interactions of M. alternifolia
(tea tree), T. vulgaris (thyme), M. piperita (peppermint) and R. officinalis
(rosemary) essential oils with amphotericin B indicate mainly antagonistic profiles
when tested against Candida albicans.
Conclusion: While a number of interactions show complete antagonism,
others show varied (synergistic, additive and ⁄ or antagonistic) interactions,
thus the efficacy is dependent on the ratio in which the two components
Significance and Impact of the Study: The predominant antagonistic interactions
noted here, suggests that some natural therapies containing essential oils
should be used with caution when combined with antibiotics.