The worldwide emergence of multi-drug resistance (MDR) in clinical Pseudomonas aeruginosa strains necessitates the development of novel therapeutic strategies and fuels the
investigation of alternative treatment options.
Given that natural substances in essential oils and extracts from plants are ethnopharmaceutically
well documented and have long been known to exert antimicrobial activity in traditional
medicine [1], we here surveyed the synergistic antimicrobial effects of clove oil (Syzygium aromaticum (L.) MEER. & L.M. PERRY) with the aminoglucoside antibiotic gentamicin against distinct
clinical MDR P. aeruginosa isolates.
The results from determinations of the minimal inhibitory concentrations (MIC) in
geometric dilution series and subsequent checkerboard used for calculations of the
fractionated inhibitory concentration index (FICI) revealed that clove oil significantly
lowered the gentamicin MIC from 8192 mg/l to ≤256. The significance of synergy was
confirmed by FIC index values of ≤ 0.0625. Notably, the concentrations of clove oil
that increase the antibiotic susceptibility significantly were with 0,25 % far below
the MIC of >8% and so did not inhibit the growth of MDR P. aeruginosa strains under investigation.
In future investigations further aminoglycoside antibiotic compounds will be analyzed
in combination with cloveoil for potential synergistic antimicrobial effects in more
clinical isolates of MDR P. aeruginosa. In addition, the molecular main components of clove oil such as eugenol and essential
oils from other plants will be examined for synergy with other antibiotics.
