Journal
BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS
Volume 324, Issue 3, Pages 1065-1068Publisher
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.bbrc.2004.09.146
Keywords
multidrug efflux; ethidium bromide; fluorescence; self-quenching; MexAB-OprM
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Funding
- NIAID NIH HHS [AI 09644] Funding Source: Medline
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Xu et al. [Biochem. Biophys. Res. Commun. 305 (2003) 941] reported that, when a mutant strain of Pseudomonas aeruginosa lacking its major multidrug efflux pump complex, MexAB-OprM, was incubated with 100 M ethidium bromide, the fluorescence, caused by its binding to DNA following its entry into cells, decreased gradually. The authors concluded that the intracellular ethidium bromide induced either its degradation or its efflux through the assembly of unknown efflux pumps. We found, through quantitation of ethidium bromide by absorption spectroscopy, that the total amount of ethidium bromide in the system remained constant under these conditions, indicating the absence of its degradation. Furthermore, intracellular ethidium bromide kept increasing during the experiment, showing that the decrease of fluorescence was due to self-quenching, and that ethidium bromide is not pumped out by a newly assembled efflux system. (C) 2004 Elsevier Inc. All rights reserved.
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