In Pseudomonas aeruginosa ethidium bromide does not induce its own degradation or the assembly of pumps involved in its efflux.
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 microM 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.
Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720, USA.
Anahit
A
Babayan
Hiroshi
H
Nikaido
D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry; D004247:DNA / Q000737:chemistry; D004996:Ethidium / Q000494:pharmacology*; D005456:Fluorescent Dyes / Q000494:pharmacology; D026901:Membrane Transport Proteins / Q000737:chemistry; D011485:Protein Binding; D011550:Pseudomonas aeruginosa / Q000378:metabolism*; D013053:Spectrophotometry; D013997:Time Factors
D001425:Bacterial Outer Membrane Proteins; D005456:Fluorescent Dyes; D026901:Membrane Transport Proteins; C118598:MexA protein, Pseudomonas aeruginosa; C118597:MexB protein, Pseudomonas aeruginosa; C402263:OprM protein, Pseudomonas aeruginosa; D004247:DNA; D004996:Ethidium