JAC Advance Access originally published online on October 27, 2009
Journal of Antimicrobial Chemotherapy 2009 64(6):1203-1211; doi:10.1093/jac/dkp381
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Original research |
Enhancing antibiotic activity: a strategy to control Acinetobacter infections
1 Natural Products Research Center and Department of Microbiology, Faculty of Science, Prince of Songkla University, Hat Yai, Songkla 90112, Thailand 2 Department of Microbiology and Immunology, University of British Columbia, 2350 Health Sciences Mall, Vancouver, BC, Canada
Received 11 August 2009; returned 1 September 2009; revised 29 September 2009; accepted 30 September 2009
* Corresponding author. Tel: +1-(604) 822-5856; Fax: +1-(604) 822-6041; E-mail: jed{at}interchange.ubc.ca
Objectives: The emergence of antibiotic resistance has seriously diminished antibiotic efficacy and an increasing number of infections are becoming difficult to treat. One approach to the restoration of antibiotic activity is to administer them in conjunction with non-antibiotic compounds that depress resistance mechanisms. We describe the activity of ellagic and tannic acids as adjuvants that enhance the activity of aminocoumarin antibiotics against multidrug-resistant (MDR) Acinetobacter baumannii.
Methods: Adjuvant activity of plant phenolics was tested using growth inhibition assays in combination with subinhibitory concentrations of novobiocin. The antibacterial susceptibilities of susceptible and MDR A. baumannii to a variety of antibiotics were determined in the absence and presence of ellagic and tannic acids. The effect of the adjuvants on bacterial outer membrane function was examined by using the fluorescence dye 1-N-phenylnaphthylamine (NPN). The efflux pump inhibition was measured by the intracellular accumulation of ethidium bromide (EtBr) and pyronin Y.
Results: At 40 µM, ellagic and tannic acids enhanced the activity of novobiocin, coumermycin, chlorobiocin, rifampicin and fusidic acid against A. baumannii. There were no increases in the uptake of NPN or in the accumulation of EtBr after strains were treated with these adjuvants; however, the intracellular accumulation of pyronin Y by the treated cells was significantly increased, suggesting that ellagic and tannic acids act as efflux pump inhibitors.
Conclusions: Susceptibility of MDR A. baumannii to a variety of antibiotics was enhanced in the presence of ellagic and tannic acids. The use of such plant compounds might provide effective treatments for resistant Gram-negative bacterial infections.
Keywords: Acinetobacter baumannii , efflux pump inhibitors , natural products , multidrug resistance