Abstract
The aim of this study was to determine the activity and synergistic mechanisms of resveratrol in combination with chlorhexidine against carbapenem-resistant Acinetobacter baumannii clinical isolates. The activity of resveratrol plus antimicrobial agents was determined by checkerboard and time-kill assay against carbapenem-resistant A. baumannii isolated from patients at the King Chulalongkorn Memorial Hospital, Bangkok, Thailand. Overexpression of efflux pumps that mediates chlorhexidine susceptibility was characterized by the ethidium bromide accumulation assay. The effect of resveratrol on the expression of efflux pump genes (adeB, adeJ, adeG abeS, and aceI) and the two-component regulators, adeR and adeS was determined by RT-qPCR. The combination of resveratrol and chlorhexidine resulted in strong synergistic and bactericidal activity against carbapenem-resistant A. baumannii. Up-regulation of adeB and aceI was induced by chlorhexidine. However, the addition of resveratrol increased chlorhexidine susceptibility with increased intracellular accumulation of ethidium bromide in A. baumannii indicating that resveratrol acts as an efflux pump inhibitor. Expression of adeB was significantly reduced in the combination of resveratrol with chlorhexidine indicating that resveratrol inhibits the AdeB efflux pump and restores chlorhexidine effect on A. baumannii. In conclusion, reduced adeB expression in A. baumannii was mediated by resveratrol suggesting that AdeB efflux pump inhibition contributes to the synergistic mechanism of resveratrol with chlorhexidine. Our finding highlights the potential importance of resveratrol in clinical applications.
Highlights
Acinetobacter baumannii has become an important opportunistic pathogen in healthcare settings worldwide [1]
Susceptibility to imipenem (Apollo Scientific, UK), colistin, rifampicin, chlorhexidine, and resveratrol (Sigma-Aldrich, Germany) was determined by broth microdilution method according to the Clinical and Laboratory Standards Institute (CLSI) guidelines [17]
Due to the limitation of treatment of carbapenem-resistant A. baumannii infection, colistin is becoming frequently used as a last alternative
Summary
Acinetobacter baumannii has become an important opportunistic pathogen in healthcare settings worldwide [1] Various nosocomial infections such as pneumonia ( ventilator-associated), wound, and bloodstream infection caused by A. baumannii are associated with significantly increased mortality in hospitalized patients those in ICU settings [2, 3]. Despite polymyxins and tigecycline being used as the last-resort drugs for the treatment of carbapenem-resistant A. baumannii infection, widespread resistance to these antibiotics was globally found [6, 7]. This highlights the limitations for the treatment of A. baumannii infection especially carbapenem-resistant strains. Combination therapies have become one of the options for treatment, in vitro activity of antibiotic combinations do not strongly correlate with clinically relevant outcome in patients [8, 9]
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