Novel inhibitory activity of the Staphylococcus aureus NorA efflux pump by a kaempferol rhamnoside isolated from Persea lingue Nees

Jes Gitz Holler*, S. Brøgger Christensen, Hans Christian Slotved, Hasse B. Rasmussen, Alfonso Gúzman, Carl Erik Olsen, Bent Petersen, Per Mølgaard

*Corresponding author

Publikation: Bidrag til tidsskriftTidsskriftartikelpeer review


Objectives: To isolate a plant-derived compound with efflux inhibitory activity towards the NorA transporter of Staphylococcus aureus. Methods: Bioassay-guided isolation was used, with inhibition of ethidium bromide efflux via NorA as a guide. Characterization of activity was carried out using MIC determination and potentiation studies of a fluoroquinolone antibiotic in combination with the isolated compound. Everted membrane vesicles of Escherichia coli cells enriched with NorA were prepared to study efflux inhibitory activity in an isolated manner. Results: The ethanolic extract of Persea lingue was subjected to bioassay-guided fractionation and led to the isolation of the known compound kaempferol-3-O-α-l-(2,4-bis-E-p-coumaroyl)rhamnoside (compound 1). Evaluation of the dose-response relationship of compound 1 showed that ethidium bromide efflux was inhibited, with an IC 50 value of 2 μM. The positive control, reserpine, was found to have an IC 50 value of 9 μM. Compound 1 also inhibited NorA in enriched everted membrane vesicles of E. coli. Potentiation studies revealed that compound 1 at 1.56 mg/L synergistically increased the antimicrobial activity of ciprofloxacin 8-fold against a NorA overexpresser, and the synergistic activity was exerted at a fourth of the concentration necessary for reserpine. Compound 1 was not found to exert a synergistic effect on ciprofloxacin against a norA deletion mutant. The 2,3-coumaroyl isomer of compound 1 has been shown previously not to cause acute toxicity in mice at 20 mg/kg/day. Conclusions: Our results show that compound 1 acts through inhibition of the NorA efflux pump. Combination of compound 1 with subinhibitory concentrations of ciprofloxacin renders a wild-type more susceptible and a NorA overexpresser S. aureus susceptible.

TidsskriftJournal of Antimicrobial Chemotherapy
Udgave nummer5
Sider (fra-til)1138-1144
Antal sider7
StatusUdgivet - maj 2012
Udgivet eksterntJa

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