pH Modulation of efflux pump activity of multi-drug resistant Escherichia coli: protection during its passage and eventual colonization of the colon.
BACKGROUND
Resistance Nodulation Division (RND) efflux pumps of Escherichia coli extrude antibiotics and toxic substances before they reach their intended targets. Whereas these pumps obtain their energy directly from the proton motive force (PMF), ATP-Binding Cassette (ABC) transporters, which can also extrude antibiotics, obtain energy from the hydrolysis of ATP. Because E. coli must pass through two pH distinct environments of the gastrointestinal system of the host, it must be able to extrude toxic agents at very acidic and at near neutral pH (bile salts in duodenum and colon for example). The herein described study examines the effect of pH on the extrusion of ethidium bromide (EB).


RESULTS
E. coli AG100 and its tetracycline induced progeny AG100(TET) that over-expresses the acrAB efflux pump were evaluated for their ability to extrude EB at pH 5 and 8, by our recently developed semi-automated fluorometric method. At pH 5 the organism extrudes EB without the need for metabolic energy (glucose), whereas at pH 8 extrusion of EB is dependent upon metabolic energy. Phe-Arg beta-naphtylamide (PAbetaN), a commonly assumed inhibitor of RND efflux pumps has no effect on the extrusion of EB as others claim. However, it does cause accumulation of EB. Competition between EB and PAbetaN was demonstrated and suggested that PAbetaN was preferentially extruded. A K(m) representing competition between PAbetaN and EB has been calculated.


CONCLUSIONS
The results suggest that E. coli has two general efflux systems (not to be confused with a distinct efflux pump) that are activated at low and high pH, respectively, and that the one at high pH is probably a putative ABC transporter coded by msbA, which has significant homology to the ABC transporter coded by efrAB of Enterococcus faecalis, an organism that faces similar challenges as it makes its way through the toxic intestinal system of the host.
Martins
Ana
A
Unit of Mycobacteriology, Universidade Nova de Lisboa (IHMT/UNL), Lisboa, Portugal.
Spengler
Gabriella
G
Rodrigues
Liliana
L
Viveiros
Miguel
M
Ramos
Jorge
J
Martins
Marta
M
Couto
Isabel
I
Fanning
Séamus
S
Pagès
Jean-Marie
JM
Bolla
Jean Michel
JM
Molnar
Joseph
J
Amaral
Leonard
L
D001692:Biological Transport; D003106:Colon / Q000382:microbiology*; D018432:Drug Resistance, Multiple; D004926:Escherichia coli / Q000254:growth & development / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008826:Microbial Sensitivity Tests
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