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Antimicrobial Agents and Chemotherapy, December 2001, p. 3375-3380, Vol. 45, No. 12
Unité des Agents Antibactériens,
Institut Pasteur, 75724 Paris Cedex 15,1 and
Centre d'Etudes Pharmaceutiques,
Châtenay-Malabry,2 France
Received 10 May 2001/Returned for modification 19 July
2001/Accepted 27 August 2001
Multidrug-resistant strain Acinetobacter baumannii
BM4454 was isolated from a patient with a urinary tract infection. The adeB gene, which encodes a resistance-nodulation-cell
division (RND) protein, was detected in this strain by PCR with two
degenerate oligodeoxynucleotides. Insertional inactivation of
adeB in BM4454, which generated BM4454-1, showed that
the corresponding protein was responsible for aminoglycoside resistance
and was involved in the level of susceptibility to other drugs
including fluoroquinolones, tetracyclines, chloramphenicol,
erythromycin, trimethoprim, and ethidium bromide. Study of ethidium
bromide accumulation in BM4454 and BM4454-1, in the presence or in the
absence of carbonyl cyanide m-chlorophenylhydrazone,
demonstrated that AdeB was responsible for the decrease in
intracellular ethidium bromide levels in a proton motive
force-dependent manner. The adeB gene was part of a
cluster that included adeA and adeC which
encodes proteins homologous to membrane fusion and outer membrane
proteins of RND-type three-component efflux systems, respectively. The
products of two upstream open reading frames encoding a putative
two-component regulatory system might be involved in the regulation of
expression of the adeABC gene cluster.
During the last 20 years
hospital-acquired infections caused by multidrug-resistant,
gram-negative bacilli have increased considerably to become a
significant health problem. Acinetobacter spp. are
ubiquitous, nonfermentative, gram-negative bacilli which play a
significant role in the colonization and infection of patients in
intensive care units. Acinetobacter baumannii is the
predominant species associated with outbreaks of nosocomial infections
(3). This opportunistic microorganism may cause epidemic
pneumonia, urinary tract infections, septicemia, and meningitis
(24). Few antibiotics are effective for the treatment of
Acinetobacter infections because of the numerous mechanisms
of resistance accumulated by isolates of this bacterial genus and the
frequency of multidrug-resistant strains. Acinetobacter
infections are thus often very difficult to treat, and combination
therapy is usually required for effective treatment (3).
Aminoglycosides can be used successfully in combination with an
effective Resistance of Acinetobacter to Efflux systems are widely found in microorganisms and confer resistance
to various compounds, including antibiotics, by extrusion of the drug.
The ATP-dependent multidrug transporters use ATP as a source of energy,
whereas the secondary multidrug transporters are sensitive to agents
that dissipate the proton motive force, suggesting that they mediate
the efflux of the toxic compounds from the cell in a coupled exchange
with protons. These secondary multidrug transporters can be subdivided
into distinct families: the major facilitator (MF) superfamily, the
small multidrug resistance (SMR) superfamily, the multidrug and toxic
compound extrusion (MATE) superfamily, and the
resistance-nodulation-cell division (RND) family (27).
Most of the multidrug transporters belonging to the RND family interact
with a membrane fusion protein (MFP) and an outer membrane protein
(OMP) to allow drug transport across both the inner and the outer
membranes of gram-negative bacteria (32, 37). The
secondary structure of RND-type efflux proteins was proposed to consist
of 12 transmembrane segments (TMSs), with two long loops between TMSs 1 and 2 and TMSs 7 and 8 (27, 32). The trimeric form of the
OMP generates a continuous, solvent-accessible "channel-tunnel"
that spans both the outer membrane and the periplasmic space (36,
13). MFP could be involved in either the bringing of the inner
and outer membranes closer or the stabilization of the OMP structure
(37, 23). Recently, three RND-type efflux pumps have been
demonstrated to be involved in aminoglycoside resistance: AmrAB-OprA,
responsible for intrinsic aminoglycoside and macrolide resistance in
Burkholderia pseudomallei (20); MexXY, which
exports aminoglycosides, tetracycline, and erythromycin from
Pseudomonas aeruginosa (19, 28, 35); and AcrD
in Escherichia coli (29).
A. baumannii BM4454, isolated from a patient with a urinary
tract infection, was resistant to multiple antibiotics with a phenotype
of aminoglycoside resistance, suggesting that resistance to this
class of drugs could be due to active efflux. The present study was
undertaken to identify the molecular mechanism that confers the
particularly broad-spectrum aminoglycoside resistance of A. baumannii BM4454. A three-component efflux system that included an
RND multidrug transporter was shown to be involved in resistance by
insertional inactivation.
Plasmids, strains, and growth conditions.
A.
baumannii BM4454 was isolated in 1999 from a patient with a
urinary tract infection at the Hôpital Saint-Michel in Paris, France. The strains were grown in brain heart infusion broth and agar
(Difco Laboratories, Detroit, Mich.) at 37°C. For BM4454-1, growth
media were supplemented with ticarcillin (80 µg/ml) in order to
maintain selection pressure.
Susceptibility testing.
Antibiotic susceptibility was tested
by disk diffusion on Mueller-Hinton agar (Bio-Rad, Marnes-la-Coquette,
France). The MICs of antibiotics were determined by the method of
Steers et al. (31) with 104 CFU per
spot on agar after 24 h of incubation. Susceptibility to ethidium
bromide and to safranin O was tested on Mueller-Hinton agar drug gradients.
DNA manipulations.
Total and plasmid DNAs were prepared as
described previously (4). Purification of plasmid DNA was
performed by using the Wizard minipreps DNA kit (Promega, Madison,
Wis.). Restriction with endonucleases was done according to the
supplier's recommendations (Life Technologies Inc., Gaithersburg,
Md.). Extraction of DNA fragments separated by agarose gel
electrophoresis was carried out by using the Sephaglas BandPrep Kit
(Pharmacia Biotech, Saint-Quentin en Yvelines, France).
0066-4804/01/$04.00+0 DOI: 10.1128/AAC.45.12.3375-3380.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Resistance-Nodulation-Cell Division-Type Efflux
Pump Involved in Aminoglycoside Resistance in Acinetobacter
baumannii Strain BM4454
ABSTRACT
Top
Abstract
Introduction
Materials and Methods
Results
Discussion
References
INTRODUCTION
Top
Abstract
Introduction
Materials and Methods
Results
Discussion
References
-lactam, and combinations of a -lactam with either a
fluoroquinolone or rifampin have also been proposed. However, treatment
failure and death caused by Acinetobacter infections or
underlying diseases are common (3).
-lactams is partially
intrinsic due to the synthesis of a species-specific cephalosporinase (11, 33). However, additional plasmid- or transposon-borne -lactamase genes can be acquired (5, 9). Mutations in
the gyrA gene have been associated with high-level
resistance to fluoroquinolones in this organism (3, 34).
Aminoglycoside resistance is also common in Acinetobacter
and results primarily from inactivation of the antibiotic by specific
modifying enzymes. Three classes of aminoglycoside-inactivating enzymes
(acetyltransferases, phosphotransferases, and adenylyltransferases)
have been identified in Acinetobacter (15).
Acinetobacter haemolyticus and related species are
intrinsically resistant to aminoglycosides by synthesis of a
chromosomally encoded specific N-acetyltransferase
[AAC(6')] (14, 30). In contrast, aminoglycoside-resistant A. baumannii isolates usually
result from the acquisition of genes encoding modifying enzymes
(15, 33). Aminoglycoside resistance mediated by an efflux
system has not yet been reported in Acinetobacter; the only
evidence for an efflux mechanism is the export of phosphonium ions in
Acinetobacter calcoaceticus (18).
MATERIALS AND METHODS
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Abstract
Introduction
Materials and Methods
Results
Discussion
References
-32P]dCTP (3,000 Ci/mmol; Amersham
Radiochemical Center, Amersham, England) with a nick translation kit (Amersham).
Detection and insertion-inactivation of adeB. The adeB gene was detected by PCR amplification of A. baumannii BM4454 total DNA with degenerate oligodeoxynucleotides O1 [5'-GT(A/T)GA(T/C)GA(T/C)GC(A/T)AT(A/T)GT(A/T)GT-3'] and O2 [5'-A(A/G)(A/T)(C/G)(A/T)(A/T)GTCAT(A/T)A(A/G)(A/T)AT(A/T)GG-3'], which were complementary to the conserved motifs D and C of the RND protein family, respectively, and which were designed by taking into account the genetic codon preference of Acinetobacter.
A fragment internal to the adeB gene of BM4454 was amplified with specific oligodeoxynucleotides O3 (5'-GTATGAATTGATGCTGC-3') and O4 (5'-CACTCGTAGCCAATACC-3') (O3 from positions 6199 to 6213 and O4 from positions 7177 to 7161, with the numbering given 5' to 3', according to the sequence with GenBank accession no. AF370885). The 979-bp amplification product was cloned into SmaI-linearized pUC18, a suicide vector in Acinetobacter (25), to generate pAT794. Plasmid pAT794 DNA was introduced into BM4454 by electrotransformation, and transformants were selected for ticarcillin resistance. Total DNA from the three clones stably resistant to ticarcillin was obtained and was analyzed by PCR with the M13 reverse primer and the M13 (
20) forward primers and with two specific primers
complementary to the flanking regions of the pAT794 insert in the
BM4454 chromosome. Total DNA from the three transformants was
restricted with ClaI and NdeI and was analyzed by
Southern hybridization with probes specific for the
blaTEM-1 gene of pUC18 and for the 3' end
of the adeB gene downstream from the O3-O4 internal
fragment. Transformant BM4454-1, the only one that contained a single
copy of pAT794 in the adeB gene, was selected for further studies.
Determination of the sequence of the ade gene
cluster.
To obtain plasmid pAT796, total DNA from BM4454-1 was
digested with NheI (Fig. 1),
self-ligated, and used to transform E. coli Top 10 competent
cells with selection on ticarcillin. DNA sequencing was performed with
specific primers with a CEQ 2000 DNA Analysis System automatic
sequencer (Beckman Instruments, Inc., Palo Alto, Calif.).
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Accumulation of ethidium bromide.
The kinetics of ethidium
bromide accumulation in BM4454 and BM4454-1 cells were monitored by a
fluorimetric assay slightly modified from that described
previously (8). Cells were grown to an optical
density at 600 nm of 0.5, pelleted carefully at room temperature,
resuspended to an A600 of 0.2 in
sodium phosphate buffer (pH 7.0), and returned to 37°C. Ethidium
bromide was added at a final concentration of 2 µg/ml, and after
420 s of incubation, carbonyl cyanide
m-chlorophenylhydrazone (CCCP) was added at a final
concentration of 100 µM. The change in fluorescence intensity (
excite, 530 nm;
emit, 600 nm), which is proportional to the quantity of intracellular dye, was recorded on an SFM 25 spectrofluorimeter (Bio-Tek Kontron Instruments, Saint-Quentin en
Yvelines, France) for 700 s following the addition of ethidium bromide.
Computer analysis of sequence data. Nucleotide sequence data were analyzed with the GCG sequence analysis software package (version 7; Genetics Computer Group, Madison, Wis.). Amino acid sequences were analyzed at the website of the National Center for Biotechnology Information (www.ncbi.nih.gov/gorf/gorf.html). The GenBank and protein databases were screened for sequence similarities.
Nucleotide sequence accession number. The 10,629-bp sequence of BM4454-1 has been deposited in the GenBank data library (GenBank, Los Alamos, N.M.) under accession no. AF370885.
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RESULTS |
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Top
Abstract
Introduction
Materials and Methods
Results
Discussion
References
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Resistance phenotype of A. baumannii BM4454.
A. baumannii BM4454 was resistant to aminoglycosides,
tetracyclines, fluoroquinolones, and
macrolides-lincosamides-streptogramins (MLS), in
addition to -lactams, to which this species has intrinsic resistance. The strain was resistant to low levels of all
aminoglycosides tested, but curiously, it was more susceptible to
kanamycin than to the others members of this drug class. Moreover, both
2'-N-ethylnetilmicin and 6'-N-ethylnetilmicin
were similarly inactive against BM4454. This resistance phenotype did
not correspond to any of the phenotypes conferred by a known
aminoglycoside-modifying enzyme or any combination of known
aminoglycoside-modifying enzymes. In our experience, clinical isolates
of A. baumannii, such as BM4454, with a broad aminoglycoside
resistance phenotype are relatively common, but aminoglycoside-modifying activity has never been detected in such strains by the phosphocellulose paper-binding assay (data not shown).
In addition, these strains exhibit an uncommonly low level of
susceptibility to norfloxacin compared to their level of susceptibility to pefloxacin. Taken together, these data suggested that aminoglycoside resistance in BM4454 could be due to active efflux of the drugs, which
certainly affected other compounds. Additionally, high-level resistance
to fluoroquinolones and MLS suggested that BM4454 had developed
multiple mechanisms for antibiotic resistance.
Detection and inactivation of Ade efflux system. In order to detect a putative efflux protein in A. baumannii BM4454, degenerate oligonucleotides O1 and O2, complementary to the conserved motifs D and C of the RND protein family, respectively (26), were used to amplify total DNA from BM4454, and the sequence of the PCR product of the expected size (ca. 1,700 bp) was determined. Comparison of the sequence with those in the GenBank database revealed a high degree of identity (approximately 50%) with internal regions of structural genes encoding RND proteins. Two specific primers, O3 and O4, deduced from this sequence, were used to amplify an internal 979-bp fragment that was ligated into pUC18 to generate recombinant suicide plasmid pAT794. Plasmid pAT794 DNA was introduced into BM4454 by electrotransformation, and transformants stably resistant to ticarcillin were found to be susceptible to aminoglycosides by disk diffusion. They were analyzed by PCR, sequence determination, and Southern hybridization. The resulting data (data not shown) allowed selection of a clone, BM4454-1, with a single integrated copy of pAT794 in the partly characterized gene, following a homologous recombination event. This indicated that the gene encoded an RND-type protein involved in aminoglycoside resistance in BM4454 and was named adeB, for Acinetobacter drug efflux. The adeB gene was detected by dot hybridization in the six A. baumannii strains tested but not in the four A. haemolyticus strains tested (data not shown).
Cloning and characterization of the genes encoding the Ade efflux
system.
Plasmid pAT796, which contained approximately 12 kb of DNA
flanking the pAT794 insertion site, was obtained by restriction of
BM4454-1 genomic DNA, followed by self-ligation and transformation into
E. coli with selection on ticarcillin. The sequence of 10.6 consecutive kb of DNA was determined, and the search for stop codons in
the three reading frames in each DNA strand revealed the presence of
seven complete open reading frames (ORF) (Fig. 1). A search of the nr
database indicated that the deduced products of the three adjacent
genes, adeA (ORF4; nucleotides 3439 to 4629), adeB (ORF5; nucleotides 4629 to 7736), and adeC
(ORF6; nucleotides 7813 to 9210) were highly similar to proteins
constituting three-component multidrug efflux systems of the RND type.
The AdeB protein consisted of 1,035 amino acids and exhibited a high
degree of identity (approximately 50%) with RND proteins (Table
1). The hydropathy profile of the deduced
AdeB sequence revealed a pattern that was duplicated in the N- and
C-terminal halves of the protein and 12 hydrophobic domains which may
correspond to the transmembrane segments of the typical RND proteins
(data not shown). AdeA was homologous to MFPs with 35 to 40% identity
(Table 1), whereas AdeC was most similar (40% identity) to the OprM
OMP from P. aeruginosa.
|
Substrate specificity of Ade pump.
The functional role of AdeB
was studied by comparing the inhibitory activities of various
antibiotics and toxic compounds against BM4454 and its derivative,
BM4454-1, in which the adeB gene had been disrupted.
Determination of the MICs of various structural classes of antibiotics
(Table 2) indicated that all antibiotics
tested, including aminoglycosides, fluoroquinolones, cefotaxime,
erythromycin, tetracycline, chloramphenicol, and trimethoprim, were
substrates for the AdeB pump since MICs were 4 to more than 32 times
higher for BM4454 than for BM4454-1. Disk diffusion indicated that
BM4454 was also significantly more resistant than BM4454-1 to
minocycline. In contrast, the activities of rifampin, sulfonamides, amoxicillin, and ceftazidime remained unchanged (data not shown). Moreover, BM4454 was able to grow on much higher concentrations of
ethidium bromide than BM4454-1 was, but both strains were inhibited at
the same concentration of the dye safranin O.
|
Accumulation of ethidium bromide.
To confirm that the
difference in drug susceptibility between BM4454 and BM4454-1 was due
to an efflux mechanism, the level of accumulation of ethidium bromide
was measured and was found to be approximately three times lower in
BM4454 than in BM4454-1 after 400 s (Fig.
2). Dissipation of the membrane proton
motive force by addition of the protonophore CCCP at 420 s
increased the level of accumulation of ethidium bromide in both
strains, resulting in similar concentrations 300 s after CCCP
addition.
|
) and BM4454-1 (
). At 420 s CCCP
was added to the bacterial suspensions at a final concentration of 100 µM.
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DISCUSSION |
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Top
Abstract
Introduction
Materials and Methods
Results
Discussion
References
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Until recently, antibiotic resistance by active efflux of the drug
was limited to hydrophobic and amphiphilic compounds, including quinolones, tetracyclines, macrolides, -lactams, chloramphenicol, and rifampin (22). In 1999, involvement of the AmrB
RND-type efflux pump in the intrinsic aminoglycoside resistance of
B. pseudomallei was reported (20).
Subsequently, disruption of mexY in P. aeruginosa (28, 19, 35) and acrD in E. coli
(29) was shown to result in aminoglycoside
hypersusceptibility. Moreover, multidrug transporters belonging to
other families, including the ABC (17), SMR
(12), MF (6, 2), and MATE (21)
superfamilies, have been shown to be able to export aminoglycosides
when their structural genes are cloned into a multicopy plasmid. We
have characterized the adeABC gene cluster (Fig. 1) from
multidrug-resistant clinical isolate A. baumannii BM4454,
which exhibited an aminoglycoside resistance pattern that could not be
explained by production of one or a combination of known
aminoglycoside-modifying enzymes. The proteins deduced from the
adeA, adeB, and adeC genes were highly
similar to MFPs, the RND proteins, and OMPs, respectively, suggesting
that these genes encode a three-component efflux system. Disruption of
the adeB gene in BM4454 demonstrated that the corresponding protein was responsible for aminoglycoside resistance and also contributed to the multiple-antibiotic-resistance phenotype of this
strain. The proteins most similar to AdeA and AdeB were MtrC from
Neisseria gonorrhoeae and MexD from P. aeruginosa, respectively (Table 1), which have not been reported
to have an ability to transport aminoglycosides.
Aminoglycosides, as well as cefotaxime, tetracyclines, erythromycin, chloramphenicol, trimethoprim, fluoroquinolones, and ethidium bromide, were found to be substrates for AdeB (Table 2). Thus, this efflux pump can apparently recognize a wide spectrum of substrates including hydrophobic, amphiphilic, and hydrophilic molecules which can be either positively charged or neutral. Among the aminoglycosides, kanamycin and amikacin appeared to be less effectively transported than other compounds by AdeABC. These two aminoglycosides contain the largest number of hydroxyl substituents and, consequently, are the most hydrophilic. In the same way, the hydrophobic fluoroquinolones ofloxacin and sparfloxacin appeared to be slightly better substrates than the more hydrophilic fluoroquinolones norfloxacin and pefloxacin. However, an additional mechanism must be involved in fluoroquinolone resistance in BM4454, and this is probably modification of the intracellular target, since BM4454-1 still exhibited high-level resistance to these molecules. This combination of mechanisms could explain the very high level of fluoroquinolone resistance of the clinical isolate.
Efflux mediated by AdeABC was confirmed by comparing the levels of intracellular accumulation of ethidium bromide by BM4454 and BM4454-1 (Fig. 2). Accumulation experiments were not carried out with radiolabeled aminoglycosides in order to test the effect of the protonophore CCCP, since this molecule dissipates the proton motive force essential for both efflux by RND pumps and uptake of aminoglycosides. The results indicate that disruption of adeB increases ethidium bromide accumulation in a CCCP-dependent fashion, supporting a proton motive force-dependent efflux mechanism for AdeB-mediated aminoglycoside resistance. Moreover, in BM4454-1 the rate of accumulation of ethidium bromide was increased in the presence of CCCP, suggesting that other efflux pumps dependent on the proton motive force may contribute to ethidium bromide efflux in A. baumannii. This is not surprising given that ethidium bromide is an efficient and common substrate for RND multidrug transporters, many of which may coexist in a single bacterium, as is illustrated by the multiple Acr and Mex efflux systems of E. coli and P. aeruginosa, respectively.
The expression of multidrug transporters is commonly controlled by specific regulatory proteins, whose structural genes are most often adjacent to those encoding the efflux system (10, 1, 16). For example, the mexZ (28) and amrR (20) genes encoding putative transcriptional repressors are located upstream from the mexXY and amrAB clusters, respectively. No such sequences were found in the environment of the adeABC genes, but three divergently transcribed ORFs were identified in the upstream region. Comparison of the sequences of the deduced proteins with those in a protein database suggested that they could code for a two-component regulatory system and a protein partly homologous to a putative transcriptional terminator-antiterminator from Mycobacterium. The genetic organization and sequence homology of ORF1, ORF2, and ORF3 suggested that the corresponding products may be involved in the regulation of adeABC expression, similar to the regulation of the norA gene in Staphylococcus aureus (7). The presence of multiple 11-bp imperfect inverted repeat sequences in the 5' end of the adeA gene is compatible with this hypothesis. The absence of the parental strain of A. baumannii BM4454 makes it difficult to characterize the event responsible for the emergence of antibiotic resistance in this clinical isolate. In order to study the possible involvement of the proteins encoded by ORF1, ORF 2, and ORF3 in adeABC transcriptional regulation, transcriptional fusions and gene inactivation experiments are in progress.
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ACKNOWLEDGMENTS |
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We thank M. Chignard and S. Dulong for help with ethidium bromide accumulation experiments.
This work was supported in part by a Bristol-Myers Squibb Unrestricted Biomedical Research Grant in Infectious Diseases. S.M. was a recipient of a doctoral fellowship from the Ministère de l'Education Nationale de la Recherche et de la Technologie and from the Fondation pour la Recherche Médicale.
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FOOTNOTES |
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* Corresponding author. Mailing address: Unité des Agents Antibactériens, Institut Pasteur, 25, rue du Dr Roux, 75724 Paris Cedex 15, France. Phone: (33) 1 45 68 83 20. Fax: (33) 1 45 68 83 19. E-mail: pcourval{at}pasteur.fr.
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REFERENCES |
|---|
|
Top
Abstract
Introduction
Materials and Methods
Results
Discussion
References
|
|---|
| 1. |
Ahmed, M.,
C. M. Borsch,
S. S. Taylor,
N. Vazquez-Laslop, and A. A. Neyfakh.
1994.
A protein that activates expression of a multidrug efflux transporter upon binding the transporter substrates.
J. Biol. Chem.
269:28506-28513 |
| 2. |
Ainsa, J. A.,
M. C. Blokpoel,
I. Otal,
D. B. Young,
K. A. De Smet, and C. Martin.
1998.
Molecular cloning and characterization of Tap, a putative multidrug efflux pump present in Mycobacterium fortuitum and Mycobacterium tuberculosis.
J. Bacteriol.
180:5836-5843 |
| 3. | Bergogne-Bérézin, E., and K. J. Towner. 1996. Acinetobacter spp. as nosocomial pathogens: microbiological, clinical, and epidemiological features. Clin. Microbiol. Rev. 9:148-165[Medline]. |
| 4. |
Birnboim, H. C., and J. Doly.
1979.
A rapid alkaline extraction procedure for screening recombinant plasmid DNA.
Nucleic Acids Res.
7:1513-1523 |
| 5. |
Devaud, M.,
F. H. Kayser, and B. Bachi.
1982.
Transposon-mediated multiple antibiotic resistance in Acinetobacter strains.
Antimicrob. Agents Chemother.
22:323-329 |
| 6. |
Edgar, R., and E. Bibi.
1997.
MdfA, an Escherichia coli multidrug resistance protein with an extraordinarily broad spectrum of drug recognition.
J. Bacteriol.
179:2274-2280 |
| 7. |
Fournier, B.,
R. Aras, and D. C. Hooper.
2000.
Expression of the multidrug resistance transporter NorA from Staphylococcus aureus is modified by a two-component regulatory system.
J. Bacteriol.
182:664-671 |
| 8. |
Giraud, E.,
A. Cloeckaert,
D. Kerboeuf, and E. Chaslus-Dancla.
2000.
Evidence for active efflux as the primary mechanism of resistance to ciprofloxacin in Salmonella enterica serovar Typhimurium.
Antimicrob. Agents Chemother.
44:1223-1228 |
| 9. | Goldstein, F. W., A. Labigne-Roussel, G. Gerbaud, C. Carlier, E. Collatz, and P. Courvalin. 1983. Transferable plasmid-mediated antibiotic resistance in Acinetobacter. Plasmid 10:138-147[CrossRef][Medline]. |
| 10. |
Hagman, K. E.,
W. Pan,
B. G. Spratt,
J. T. Balthazar,
R. C. Judd, and W. M. Shafer.
1995.
Resistance of Neisseria gonorrhoeae to antimicrobial hydrophobic agents is modulated by the mtrRCDE efflux system.
Microbiology
141:611-622 |
| 11. |
Hood, J., and S. G. B. Amyes.
1991.
The chromosomal -lactamases of the genus Acinetobacter: enzymes which challenge our imagination, p. 117-132.
In
K. J. Towner, and C. A. Fewson (ed.), The biology of Acinetobacter. Plenum Publishing Corp., New York, N.Y.
|
| 12. |
Jack, D. L.,
M. L. Storms,
J. H. Tchieu,
I. T. Paulsen, and M. H. Saier.
2000.
A broad-specificity multidrug efflux pump requiring a pair of homologous SMR-type proteins.
J. Bacteriol.
182:2311-2313 |
| 13. | Koronakis, V., A. Sharff, E. Koronakis, B. Luisi, and C. Hughes. 2000. Crystal structure of the bacterial membrane protein TolC central to multidrug efflux and protein export. Nature 405:914-919[CrossRef][Medline]. |
| 14. |
Lambert, T.,
G. Gerbaud,
M. Galimand, and P. Courvalin.
1993.
Characterization of an Acinetobacter haemolyticus aac(6')-Ig gene encoding an aminoglycoside 6'-N-acetyltransferase which modifies amikacin.
Antimicrob. Agents Chemother.
37:2093-2100 |
| 15. | Lambert, T., E. Rudant, P. Bouvet, and P. Courvalin. 1997. Molecular basis of aminoglycoside resistance in Acinetobacter spp. J. Med. Microbiol. 46:731-735. |
| 16. | Ma, D., M. Alberti, C. Lynch, H. Nikaido, and J. E. Hearst. 1996. The local repressor AcrR plays a modulating role in the regulation of acrAB genes of Escherichia coli by global stress signals. Mol. Microbiol. 19:101-112[CrossRef][Medline]. |
| 17. |
Masuda, N.,
E. Sakagawa,
S. Ohya,
N. Gotoh,
H. Tsujimoto, and T. Nishino.
2000.
Substrate specificities of MexAB-OprM, MexCD-OprJ, and MexXY-OprM efflux pumps in Pseudomonas aeruginosa.
Antimicrob. Agents Chemother.
44:3322-3327 |
| 18. | Midgley, M., N. S. Iscandar, and E. A. Daves. 1986. The interaction of phosphonium ions with Acinetobacter calcoaceticus: evidence for the operation of an efflux system. Biochim. Biophys. Acta 856:45-49[CrossRef]. |
| 19. |
Mine, T.,
Y. Morita,
A. Kataoka,
T. Mizushima, and T. Tsuchiya.
1999.
Expression in Escherichia coli of a new multidrug efflux pump, MexXY, from Pseudomonas aeruginosa.
Antimicrob. Agents Chemother.
43:415-417 |
| 20. |
Moore, R. A.,
D. Deshazer,
S. Reckseidler,
A. Weissman, and D. E. Woods.
1999.
Efflux-mediated aminoglycoside and macrolide resistance in Burkholderia pseudomallei.
Antimicrob. Agents Chemother.
43:465-470 |
| 21. |
Morita, Y.,
K. Kodama,
S. Shiota,
T. Mine,
A. Kataoka,
T. Mizushima, and T. Tsuchiya.
1998.
NorM, a putative multidrug efflux protein of Vibrio parahaemolyticus and its homolog in Escherichia coli.
Antimicrob. Agents Chemother.
42:1778-1782 |
| 22. | Nikaido, H. 1998. Antibiotic resistance caused by gram-negative multidrug efflux pumps. Clin. Infect. Dis. 27(Suppl. 1):32-41. |
| 23. | Nikaido, H. 2000. How do exported proteins and antibiotics bypass the periplasm in gram-negative bacterial cells? Trends Microbiol. 8:481-483[CrossRef][Medline]. |
| 24. | Noble, W. C. 1991. Hospital epidemiology of Acinetobacter infection, p. 53-62. In K. J. Towner, and C. A. Fewson (ed.), The biology of Acinetobacter. Plenum Publishing Corp., New York, N.Y. |
| 25. |
Palmen, R.,
B. Vosman,
P. Buijsman,
C. K. Breek, and K. J. Hellingwerf.
1993.
Physiological characterization of natural transformation in Acinetobacter calcoaceticus.
J. Gen. Microbiol.
139:295-305 |
| 26. |
Paulsen, I. T.,
M. H. Brown, and R. A. Skurray.
1996.
Proton-dependent multidrug efflux systems.
Microbiol. Rev.
60:575-608 |
| 27. |
Putman, M.,
H. W. van Veen, and W. N. Konings.
2000.
Molecular properties of bacterial multidrug transporters.
Microbiol. Mol. Biol. Rev.
64:672-693 |
| 28. |
Ramos Aires, J.,
T. Köhler,
H. Nikaido, and P. Plésiat.
1999.
Involvement of an active efflux system in the natural resistance of Pseudomonas aeruginosa to aminoglycosides.
Antimicrob. Agents Chemother.
43:2624-2628 |
| 29. |
Rosenberg, E. Y.,
D. Ma, and H. Nikaido.
2000.
AcrD of Escherichia coli is an aminoglycoside efflux pump.
J. Bacteriol.
182:1754-1756 |
| 30. | Rudant, E., P. Bouvet, P. Courvalin, and T. Lambert. 1999. Phylogenetic analysis of proteolytic Acinetobacter strains based on the sequence of genes encoding aminoglycoside 6'-N-acetyltransferases. Syst. Appl. Microbiol. 22:59-67[Medline]. |
| 31. | Steers, E., E. L. Foltz, B. S. Graves, and J. Riden. 1959. An inocula replicating apparatus for routine testing of bacterial susceptibility to antibiotics. Antibiot. Chemother. (Basel) 9:307-311. |
| 32. | Tseng, T. T., K. S. Gratwick, J. Kollman, D. Park, D. H. Nies, A. Goffeau, and M. H. Saier. 1999. The RND permease superfamily: an ancient, ubiquitous and diverse family that includes human disease and development proteins. J. Mol. Microbiol. Biotechnol. 1:107-125[Medline]. |
| 33. |
Vila, J.,
A. Marcos,
F. Marco,
S. Abdalla,
Y. Vergara,
R. Reig,
R. Gomez-Lus, and T. Jimenez de Anta.
1993.
In vitro antimicrobial production of beta-lactamases, aminoglycoside-modifying enzymes, and chloramphenicol acetyltransferase by and susceptibility of clinical isolates of Acinetobacter baumannii.
Antimicrob. Agents Chemother.
37:138-141 |
| 34. | Vila, J., J. Ruiz, P. Goni, A. Marcos, and T. Jimenez de Anta. 1995. Mutation in the gyrA gene of quinolone-resistant clinical isolates of Acinetobacter baumannii. Antimicrob. Agents Chemother. 39:1201-1203[Abstract]. |
| 35. |
Westbrock-Wadman, S.,
D. R. Sherman,
M. J. Hickey,
S. N. Coulter,
Y. Q. Zhu,
P. Warrener,
L. Y. Nguyen,
R. M. Shawar,
K. R. Folger, and C. K. Stover.
1999.
Characterization of a Pseudomonas aeruginosa efflux pump contributing to aminoglycoside impermeability.
Antimicrob. Agents Chemother.
43:2975-2983 |
| 36. |
Wong, K. K.,
F. S. Brinkman,
R. S. Benz, and R. E. Hancock.
2001.
Evaluation of a structural model of Pseudomonas aeruginosa outer membrane protein OprM, an efflux component involved in intrinsic antibiotic resistance.
J. Bacteriol.
183:367-374 |
| 37. | Zgurskaya, H. I., and H. Nikaido. 2000. Multidrug resistance mechanisms: drug efflux across two membranes. Mol. Microbiol. 37:219-225[CrossRef][Medline]. |
Antimicrobial Agents and Chemotherapy, December 2001, p. 3375-3380, Vol. 45, No. 12
0066-4804/01/$04.00+0 DOI: 10.1128/AAC.45.12.3375-3380.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
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