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Antimicrobial Agents and Chemotherapy, November 2000, p. 3237-3238, Vol. 44, No. 11
0066-4804/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
LETTERS TO THE EDITOR
Differences in Sensitivity to PA-1806 among Iron Transport
Mutants of Pseudomonas aeruginosa Compared to
Escherichia coli
 |
LETTER |
Infections by the opportunistic pathogen Pseudomonas
aeruginosa are difficult to treat because of prevalent antibiotic
resistance among the strains. Some 
-lactam-catechol-containing
derivatives have been shown to have excellent antibacterial activity
against a variety of gram-negative bacteria, including P. aeruginosa (2, 8).
Previously, a catechol-containing monobactam called BMS-180680 (now
referred to as PA-1806), containing a catechol analog directly linked
to the oxime side chain of the monobactam nucleus, was reported to have
in vitro activity against gram-negative bacteria, including P. aeruginosa (4). Characterization of the uptake of the
drug into bacterial cells was tested using iron transport mutants of
Escherichia coli. It was shown that for the tonB
mutants and the cir fiu double mutants the MICs of PA-1806
were the highest. We investigated whether similar P. aeruginosa strain PAO1 iron transport mutants would display the
same PA-1806 sensitivity profiles.
Several iron transport mutants of P. aeruginosa strain PAO1
were constructed, including an insertion mutation in fiu
(GenBank accession no. AF276976), a deletion mutation of
tonB1 (there are two tonB loci
[9]), an insertion mutation in cir (GenBank accession no. AF290511), a deletion mutation in fptA (chosen because we believed it would not be affected by PA-1806
[1]), and a double mutation in cir and
fiu. Sensitivity of these iron-regulated PAO1 mutants to the
antibacterial catechol-monobactam compound PA-1806 (supplied by
Bristol-Meyers Squibb) were compared to those of similar E. coli mutants using agar dilution MIC determinations (7). For E. coli, single mutations in
fhuE, fiu, or cir had no effect on the
entry of PA-1806 into the cells (Table
1). Likewise, single mutations in
fptA or cir of P. aeruginosa did
not affect the bacterial cells' exposure to PA-1806. For both E. coli and P. aeruginosa, tonB mutations
rendered the species resistant to PA-1806. TonB couples with outer
membrane proteins to assist in the transport of material across the
outer membrane (10), and both species appear to need TonB
for entry of PA-1806. However, a single insertion mutation in the
fiu gene of strain PAO1 resulted in the highest MIC among
all of the PAO1 mutants tested, matching the level of resistance
observed for the E. coli cir fiu double mutant. A PAO1
double mutation in cir and fiu did not add
additional resistance against PA-1806. These data suggest that besides
TonB, the Cir and Fiu proteins are also needed by E. coli
cells for the transport of monomeric catechols (3, 5, 6, 8), but apparently P. aeruginosa may need only the Fiu and TonB
proteins to bring catecholic agents into the cell.
| |
ACKNOWLEDGMENTS |
We thank the Pseudomonas aeruginosa genome sequencing
project, Klaus Hantke for E. coli iron binding mutants and
advice on the fiu homolog, Paul Phibbs and Steve Lory for
providing the PAO1 strain, Herbert Schweizer for plasmids and advice,
Lettie Goltry and Ernie Tollentino for oligonucleotide synthesis, and Scott Mizoguchi and Micki Lagrou for compilation of the raw sequence data.
| |
FOOTNOTES |
*
Phone:
(608) 785-6980
Fax: (608) 785-6959
E-mail: schwan.will{at}uwlax.edu.
| |
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| | | | |
William R. Schwan*
Department of Microbiology
University of Wisconsin La Crosse
1725 State St.
La Crosse, Wisconsin 54601
|
| | | | |
Lynn Barker
Linnea L. Brody
Pathogenesis Corporation
Seattle, Washington 98119
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Antimicrobial Agents and Chemotherapy, November 2000, p. 3237-3238, Vol. 44, No. 11
0066-4804/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
