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Journal of Clinical Microbiology, September 1998, p. 2690-2695, Vol. 36, No. 9
0095-1137/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Stable Phenotypic Resistance of Candida
Species to Amphotericin B Conferred by Preexposure to Subinhibitory
Levels of Azoles
Jose A.
Vazquez,1,2,*
Maria T.
Arganoza,2
Dina
Boikov,2
Stephanie
Yoon,2
Jack D.
Sobel,2 and
Robert A.
Akins3
Department of Biochemistry and Molecular
Biology3 and
Division of Infectious
Diseases, Department of Medicine,2 Wayne State
University School of Medicine, and
Veterans Administration
Medical Center,1 Detroit, Michigan
Received 16 March 1998/Returned for modification 11 April
1998/Accepted 13 June 1998
 |
ABSTRACT |
The fungicidal activity of amphotericin B (AmB) was quantitated for
several Candida species. Candida albicans and
C. tropicalis were consistently susceptible to AmB, with
less than 1% survivors after 6 h of exposure to AmB. C. parapsilosis and variants of C. lusitaniae and
C. guilliermondii were the most resistant, demonstrating 50 to 90% survivors in this time period and as high as 1% survival after
a 24-h exposure time. All Candida species were killed
(<1% survivors) after 24 h of exposure to AmB. In contrast,
overnight exposure to either fluconazole or itraconazole resulted in
pronounced increases in resistance to subsequent exposures to AmB. Most
dramatically, C. albicans was able to grow in AmB cultures
after azole preexposure. Several other Candida species did
not grow in AmB but showed little or no reduction in viability after up
to 24 h in AmB. Depending on the growth conditions,
Candida cells preexposed to azoles may retain AmB
resistance for days after the azoles have been removed. If this in
vitro antagonism applies to the clinical setting, treatment of patients
with certain antifungal combinations may not be beneficial. The ability
of some Candida isolates to survive transient exposures to
AmB was not reflected in the in vitro susceptibility changes as
measured by standard MIC assays. This finding should be considered in
studies attempting to correlate patient outcome with in vitro susceptibilities of clinical fungal isolates. Patients who fail to
respond to AmB may be infected with isolates that are classified as
susceptible by standard in vitro assays but that may be resistant to
transient antifungal exposures which may be more relevant in the
clinical setting.
| |
INTRODUCTION |
Consideration of the interactions
between azoles and amphotericin B (AmB) has become clinically
significant in recent years. Fluconazole and, to a lesser extent,
itraconazole are widely used and largely effective but are not
fungicidal. An additional limitation is that they are not effective
against several Candida species, notably Candida
krusei and C. glabrata (2, 4, 11, 17). AmB
is a potent, fungicidal agent that is effective against most isolates
of Candida but that has toxic side effects (1,
39). In addition, several Candida species, including
C. lusitaniae, demonstrate intrinsic resistance to AmB
(2, 6, 18, 19, 34, 35). Recent reports suggest that
antifungal therapy may select for AmB-resistant variants of C. albicans and other susceptible species (5, 10, 14-16, 20,
21, 23, 35). However, mutants verified by in vitro testing to be
resistant remain elusive (10). Inadvertent clinical
selection for resistance to AmB may be more likely due to prolonged
azole use than to AmB therapy. Some mutations in C. albicans
that confer resistance to fluconazole act by altering the synthesis of
ergosterol, the putative target of AmB action, and thereby confer
cross-resistance (19).
We previously demonstrated that preexposing C. albicans in
vitro to fluconazole or itraconazole conferred resistance to otherwise fungicidal concentrations of AmB (37). Depending on the
conditions, up to 100% of the preexposed cells tolerated AmB at 2 µg/ml for up to 24 h. However, simultaneous exposure of C. albicans to azoles and AmB had much less effect, with only a small
increase in the Candida population surviving relative to
controls exposed to AmB alone. Moreover, several investigators have
found synergistic interactions by simultaneous exposure of C. albicans to azoles and AmB (13, 30). One group, on the
other hand, described antagonisms with preexposures of
Candida to the more lipophilic azoles, such as itraconazole,
but not to fluconazole (31, 32).
In this paper, we offer new observations describing the complex
azole-AmB interactions. First, we compare the fungicidal effects of AmB
on representative isolates of six species of Candida. We are
able to show differences in AmB killing rates among some of these
Candida isolates. Second, and most importantly, preexposure to azoles decreased the susceptibilities of all Candida
species that were otherwise found to be susceptible to AmB by
standardized in vitro susceptibility studies. C. albicans
and, to a lesser extent, C. tropicalis demonstrated the
greatest degree of antagonism. C. albicans was unique in
that preexposure to azoles routinely allowed growth, not just survival,
during subsequent incubations in AmB. Third, we show that
fluconazole-mediated AmB tolerance is established by just a few hours
of exposure to fluconazole. The protection endures for several days
after azoles are removed, but only if the cells are maintained in a
nongrowing state or if the exposure to AmB is continuous following
azole incubation.
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MATERIALS AND METHODS |
Candida isolates.
The organisms tested included
123 clinical specimens recovered from individual patients at Harper
Hospital, Detroit, Mich. The distribution of species included 93 C. albicans specimens, 25 C. tropicalis
specimens, and 5 C. parapsilosis specimens. Representative isolates for each of six Candida species were chosen from
the American Type Culture Collection (Table
1). Candida species were identified by germ tube and chlamydospore formation, morphology, Yeast
API 20C method (bioMerieux, Hazelwood, Mo.) results, the phenotype on
CHROMagar Candida plates (26), and the results of
randomly amplified polymorphic DNA fingerprinting (33).
Drugs and reagents.
Antifungal agents approved for clinical
use were used in the study, so that the results of in vitro studies
would more closely approximate the potential results of in vivo
studies. The following antifungal agents were used: AmB (as a
lyophilized cake of AmB and sodium deoxycholate [Gensia Laboratories,
Irvine, Calif.]); the AmB was suspended in sterile water at 1 mg/ml
and stored frozen in light-protected vials), itraconazole (Janssen
Pharmaceuticals, Titusville, N.J.), and fluconazole (Pfizer-Roerig,
Inc., New York, N.Y.). Ergosterol was purchased from Sigma Chemicals,
Inc. (St. Louis, Mo.), and dissolved at 5 µg/ml in chloroform. This
was diluted into sterile yeast nitrogen base (YNB) medium supplemented with Tween 80, and the mixture was boiled with vigorous stirring to
facilitate dispersement (12). For experiments that involved ergosterol, the control medium had the identical concentration of Tween
80.
Fungicidal activity assays.
The fungicidal effects of AmB
were determined as previously described (37). Briefly,
overnight cultures of each isolate were inoculated in YNB media with or
without fluconazole (50 µg/ml). After an additional 14 h of
incubation, cultures were diluted 50-fold into 1-ml cultures of YNB
plus 2 µg of AmB per ml. The viabilities of these cultures were
determined as indicated below. In some experiments, overnight cultures
in fluconazole were incubated continuously in drug-free media, with or
without daily subculturing.
Susceptibility studies.
The MICs for all of the
representative ATCC isolates were determined in accordance with the
National Committee for Clinical Laboratory Standards M27-A standards by
a broth microdilution method (38).
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RESULTS |
Individual Candida isolates are killed by AmB at
distinctive rates.
To measure the susceptibility of
Candida cells to short-term exposures of AmB, freshly grown,
overnight cultures were diluted 50-fold to 0.5 × 106
to 1 × 106 cells/ml and supplemented with AmB,
typically at 2 µg/ml. At present time intervals, as well as at
initial time points, yeast cultures were sampled, diluted, and
plated on Sabouraud (SAB) agar to determine the number and percentage
of surviving cells. Control cultures without AmB exposure always grew
during the incubation interval.
Figure 1 shows that individual isolates
of four Candida species vary in susceptibility to AmB
killing in 24-h exposures. The disparity among the different
Candida species is most pronounced at 2 µg/ml. C. albicans is the most susceptible, with only about 1 in
106 cells surviving, while C. parapsilosis and
C. krusei fare better, showing losses in viability of
only 1 or 2 orders of magnitude. C. glabrata typically shows
an intermediate level of survival. These relative survival levels among
species were reproducible in three experiments.
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FIG. 1.
Fungicidal effects of AmB on Candida species.
Cultures were grown overnight and subcultured into YNB broth plus AmB
at the indicated concentrations. After 24 h viability was
determined by plating serial dilutions on SAB agar. The densities of
control cultures incubated in the same way but without AmB increased
more than 10-fold above the initial density, for all species. Ca,
C. albicans; Ck, C. krusei; Cp, C. parapsilosis; Tg, C. glabrata.
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Figure
2 shows killing rates for four
Candida species, each from an average of three to seven
experiments.
C. albicans,
C. lusitaniae, and
C. tropicalis are highly susceptible, with less
than 0.1%
survival after 8 h of exposure to AmB. The least susceptible
of
these four species was
C. parapsilosis, with about a 1%
survival
rate even after 24 h in AmB.
C. guilliermondii
and
C. glabrata were about as susceptible as
C. tropicalis (data not shown). In
most cases, viability reached its
minimum after 8 h of AmB exposure.
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FIG. 2.
Kill rates of Candida by AmB after azole
exposure. Overnight cultures were exposed to 2 µg of AmB per ml for
the indicated periods of time before serial dilutions were plated to
determine viability (open circles). Parallel cultures were treated
similarly after preexposure to either 50 µg of fluconazole per ml
(solid circles) or 2 µg of itraconazole per ml (squares) for 16 h. Panels: upper left, C. albicans, upper right, C. lusitaniae; lower left, C. tropicalis; lower right,
C. parapsilosis.
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Preexposure to azoles confers a decreased AmB fungicidal
effect.
Growth of all tested Candida species in 50 µg
of fluconazole per ml before exposure to AmB resulted in dramatic
decreases in AmB fungicidal activity. In the acidic YNB broth,
this concentration of fluconazole is insufficient to inhibit
growth to confluency, even though it is effective for most
species in the same medium buffered with 100 mM sodium phosphate, pH
7.0 (37). Figure 2 shows that preexposed C. lusitaniae maintained at least 5% viability, that about
half of preexposed C. parapsilosis cells remained
viable, and that C. tropicalis and especially
C. albicans grew in 2 µg of AmB per ml over a 24-h period.
Cultures of C. albicans, uniquely among all tested species,
became visibly turbid during this incubation. C. krusei and
C. glabrata isolates were protected to the same extent, 0.1 to 0.01% of initially viable cells remaining viable, as C. tropicalis (data not shown).
Presumably cells adapt to fluconazole and in so doing become resistant
to subsequent AmB exposure. To determine the time required
for this
adaptation, overnight cultures of cells were diluted
into replicate
1-ml cultures of YNB plus fluconazole as described
above and at hourly
intervals AmB was added to 2 µg/ml. Viable
cells were assayed 24 h later (Fig.
3). In two independent
experiments,
cells were not protected after incubation for 1 to 2 h in fluconazole
but were protected after 3 to 4 h of incubation
(Fig.
3).
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FIG. 3.
Time course of fluconazole protection. In independent
tests (triangles and circles), C. albicans cells were
diluted from overnight cultures and the mixture was supplemented with
50 µg of fluconazole per ml at time 0, while AmB at 2 µg/ml was
added at the indicated intervals. Viability was determined as described
for Fig. 1.
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Is a 3- to 4-h fluconazole preincubation protective, or does it just
allow sufficient time for growth of the yeast cells to
a density at
which AmB is less effective? To test this, yeast
cells were incubated
in the same concentration of AmB as previously
used, but at initial
densities of 2×, 5×, 10×, and 20× relative
to the early cultures
that were used in Fig.
3. No survivors were
detected in the same
time frame (data not shown), indicating that
AmB killing is density
independent. The protection is as effective
at AmB concentrations of
>6 µg/ml.
Azole-mediated resistance to AmB is maintained in nongrowing
C. albicans for days after azole exposure.
How stable
is the protective effect of azole exposure? This was addressed in two
different experiments. In the first experiment, C. albicans
cells were exposed to azoles as described for Fig. 2 and then incubated
for 0, 1, 2, or 3 days in drug-free YNB broth at 30°C with shaking
and without subculturing. After each day of drug-free incubation, cells
were transferred to new cultures supplemented with AmB as before. Cell
viability was assayed after 24 h of incubation. Figure
4 demonstrates that cells under these conditions remained resistant to AmB throughout the 3-day incubation. In contrast, controls that had no preexposure to fluconazole but that
were otherwise treated identically were not protected, i.e., were
highly susceptible to AmB.
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FIG. 4.
Duration of azole-mediated protection from AmB killing.
Cultures preexposed to azole were exposed to 2 µg of AmB per ml after
0, 1, 2, or 3 days of incubation in drug-free YNB broth. In one series,
cultures were subcultured daily into fresh YNB broth (dashed lines). In
a second series (solid lines), cultures were continuously incubated
without subculturing until they were exposed to AmB. FLZ, fluconazole;
ITZ, itraconazole.
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In the second experiment, azole-exposed cells were subcultured daily in
drug-free YNB media and grown overnight, thus allowing
nearly
continuous growth of cells. After each subculture and day
of drug-free
growth, they were diluted into YNB plus 2 µg of AmB
per ml. After
24 h of incubation, cultures were assayed for viability.
Such
cells retained AmB resistance, i.e., retained a high level
of
viability, after 1 day of growth in drug-free media after azole
exposure. However, after two or more days of this drug-free growth,
these cells become as susceptible as cells that were never exposed
to azoles (Fig.
4).
C. albicans was also exposed to fluconazole overnight,
followed by daily serial passage in YNB plus AmB without fluconazole
for 10 days. This culture continued to grow to stationary phase
at
approximately the same rate and to the same final turbidity
as a
parallel control culture with no AmB.
Intraspecies variability in AmB susceptibility.
Are isolates
within a species of Candida equally susceptible to AmB
killing? Among 93 random isolates of C. albicans, 91 were completely killed by a 24-h AmB incubation (Table
2). The five C. parapsilosis isolates demonstrated the highest percentage of survivors of any Candida isolates tested. Results for these
species are consistent with those for their representative isolates
(Fig. 1). In contrast, 12 of 25 C. tropicalis isolates
showed a low but detectable percentage of survivors after a 24-h AmB
incubation. This seems to indicate heterogeneity among isolates of this
species.
Survivors of 24-h exposures to AmB are not AmB-resistant
variants.
Exposure of C. albicans and C. tropicalis to 2 µg of AmB per ml reduced viability by a factor
of about 106, often below the level of detection of any
survivors in 1-ml cultures. To determine whether rare survivors were
stable, resistant variants, we exposed large populations of resistant
variants from each species in 500-ml cultures at the same density
(about 106/ml) to AmB. Approximately 1,000 cells survived
and grew into colonies. These cells were pooled and reevaluated in the
same way. There was no difference in survival noted. If even a single colony (conservatively, 106 cells) generated from the 1,000 survivors was persistently resistant, the second-generation selection
would have produced at least 105 colonies, more if a
putative resistant colony grew during the 24-h period of AmB exposure,
instead of the observed 1,000 colonies. Therefore, none of the
surviving colonies were stable AmB-resistant mutants.
Effects of ergosterol supplementation on AmB susceptibility.
Does fluconazole act by depleting membranes of ergosterol, causing
subsequent tolerance to AmB by removing its target? If so, adding
ergosterol to the media during the fluconazole incubation may allow
replacement in the membrane of ergosterol over less-favored lanosterol
derivatives and thus restore the target for AmB and susceptibility to
AmB.
Ergosterol is highly insoluble in YNB and must be solubilized with
Tween 80. Under these conditions, the effect of exogenous
ergosterol on AmB susceptibility is apparent (Fig.
5). As the
concentration of ergosterol in
the medium increases, the fungicidal
effect of AmB decreases, when a
fixed concentration of AmB is
used on identical aliquots of
C. albicans cells. This result shows
that the ergosterol is
solubilized freely into the medium where
it antagonizes AmB activity,
presumably by competing for AmB binding
with the membrane-bound
ergosterol.
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FIG. 5.
Effects of exogenous ergosterol on AmB killing and
azole-mediated protection from AmB killing. (A) Ergosterol at the
indicated final concentrations was added to YNB-2 µg of AmB per ml.
C. albicans viabilities were determined after 24 h.
Control cultures at each concentration of ergosterol, without AmB, all
grew to confluency in the same 24-h period. (B) Cultures were
supplemented with 35 µg of ergosterol per ml during a 16-h
fluconazole exposure before a 24-h incubation in 2 µg of AmB (+A).
Control cultures received either no ergosterol, no azole ( F), or no
AmB (A).
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The next experiment shows that cells exposed to fluconazole in medium
containing the highest level of ergosterol, 35 µg/ml,
were as
resistant to subsequent AmB exposure as control cells
in
ergosterol-free medium (Fig.
5B). In both cases, fluconazole
allowed
growth of azole-pretreated cells during the 24-h exposure
to AmB,
whereas control cultures not pretreated with azole were
effectively
killed by AmB. Thus, a simple incorporation of ergosterol
into the
membrane either did not occur or was not effective in
reversing
fluconazole-mediated protection.
| |
DISCUSSION |
The results presented here demonstrate different kill rates of the
individual Candida species by AmB. These differences may be
important in choosing antifungal therapy, since AmB is rapidly absorbed
or sequestered from the blood (7-9, 36). Hence, infecting cells may be transiently exposed to the highest fungicidal
concentrations of AmB in serum.
Much more dramatic than species-to-species variation in AmB killing
rates, however, were the levels of protection afforded by preincubation
with fluconazole. C. albicans, the Candida
species most susceptible to AmB, is able to grow in high concentrations of AmB after overnight exposure to azoles. In addition, the
preincubation concentration does not need to inhibit growth. A
concentration of 50 µg of fluconazole per ml is an effective
protectant in YNB medium at pH 5.6 or 7.0, even though fluconazole is
only inhibitory at the higher pH (37). Furthermore,
fluconazole affords AmB protection even to those species such as
C. krusei that are not susceptible to fluconazole.
A brief 3-h exposure to fluconazole suffices to establish protection
from AmB killing. On the other hand, simultaneous exposure to both
antifungals in vitro is lethal. This suggests that a process of
adaptation to fluconazole may occur; this process then protects the
cells during exposure to AmB. Given the short adaptation period, it
seems unlikely that this effect is due to replacement of membrane ergosterol with a methylated sterol derivative that is not interactive with AmB, but this has not yet been investigated.
Incubation of C. albicans, C. krusei,
C. parapsilosis, and C. tropicalis in
fluconazole results in the depletion of ergosterol and the accumulation
of lanosterol derivatives (28), the expected consequence of
inhibiting lanosterol 14-
-demethylase. Ergosterol is normally
synthesized de novo by yeasts even if it is available in the culture
medium (22). However, under conditions which preclude
ergosterol synthesis, notably anaerobiosis, it is imported efficiently
(27). Under these conditions, other sterols such as
cholesterol can substitute for ergosterol (24). If similar inhibitions promote ergosterol uptake in C. albicans,
then one would expect ergosterol to reverse fluconazole-mediated
protection from AmB. In our studies, however, it did not reverse the
azole protection, suggesting that either exogenous ergosterol uptake did not occur or that ergosterol depletion is not the only mechanism involved in this interaction. Fluconazole does not block the ergosterol biosynthetic pathway but allows the formation of downstream
C-14--methyl sterol derivatives (3, 19). A reasonable
interpretation of the inability of ergosterol supplementation to
reverse fluconazole-mediated protection from AmB, then, is that
ergosterol uptake is not permitted in the presence of the
C-14--methyl derivatives of lanosterol. More work is required to
establish this and to determine if fluconazole mediates protection by
another route. The latter is also suggested by the rapid rate at which
protection is acquired.
A recent study shows that the MLC, the minimum lethal concentration,
assayed at 2 days, was an effective predictor of microbiological failure in the patient. Furthermore, MICs were not effective predictors and were not correlated with MLCs (25). This is consistent
with our observed lack of correlation among individual isolates between their MICs and their susceptibilities in our fungicidal activity assay.
We did not assay this collection by using the E-test (38) or
by doing MIC tests in antibiotic medium no. 3 (29). Since these are reported to be more sensitive in detecting AmB resistance, they may have shown more correlation with the fungicidal activity assay
in this study. However, both of these tests depend on the growth of
putative resistant isolates in the continuous presence of AmB. It is
becoming clear that the most clinically useful assay for AmB
susceptibility will ultimately be one that measures the extent to which
an isolate survives exposure, not whether it grows in the presence of a
given concentration.
Clinical implications of this study are apparent. If patients fail to
respond to fluconazole, they are frequently switched to AmB. Our in
vitro data suggests that these sequential treatments may be
counterproductive. The protective effect of the azole lasts long after
it is removed if the exposed cells are not actively growing or if they
are maintained in AmB continuously. Cells that have adapted to AmB
will, however, not appear resistant by any current standard assay in
vitro after they have been subcultured in vitro in the absence of the
drug; such isolates would have to be isolated from the patient directly
under selective conditions. Furthermore, in an in vivo environment,
even simultaneous exposure may have the same effect as sequential
exposures in vitro, because of unknown and potentially variable
pharmacokinetic differences of the two drugs in the patient. Finally,
the degree to which this antagonism is clinically relevant depends on
the Candida species and perhaps on the individual isolate,
since some Candida species are not inhibited by AmB after
azole exposure and have the ability to grow in its presence.
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FOOTNOTES |
*
Corresponding author. Mailing address: Harper Hospital,
3990 John R, 4 Yellow Center, Detroit, MI 48201. Phone: (313) 745-9649. Fax: (313) 993-0302. E-mail: jvazquez{at}oncgate.roc.wayne.edu.
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REFERENCES |
| 1.
|
Abadi, J.
1995.
Amphotericin B.
Pediatr. Rev.
16:363-364[Abstract/Free Full Text].
|
| 2.
|
Arias, A.,
M. P. Arevalo,
A. Andreu,
C. Rodriguez, and A. Sierra.
1996.
Candida glabrata: in vitro susceptibility of 84 isolates to eight antifungal agents.
Chemotherapy
42:107-111[Medline].
|
| 3.
|
Bard, M.,
N. D. Lees,
T. Turi,
D. Craft,
L. Cofrin,
R. Barbuch,
C. Koegel, and J. C. Loper.
1993.
Sterol synthesis and viability of erg11 (cytochrome P450 lanosterol demethylase) mutations in Saccharomyces cerevisiae and Candida albicans.
Lipids
28:963-967[Medline].
|
| 4.
|
Barry, A. L., and S. D. Brown.
1996.
In vitro studies of two triazole antifungal agents (voriconazole [UK-109,496] and fluconazole) against Candida species.
Antimicrob. Agents Chemother.
40:1948-1949[Abstract].
|
| 5.
|
Berenguer, J.,
T. M. Diaz-Guerra,
B. Ruiz-Diez,
J. C. Bernaldo de Quiros,
J. L. Rodriguez-Tudela, and J. V. Martinez-Suarez.
1996.
Genetic dissimilarity of two fluconazole-resistant Candida albicans strains causing meningitis and oral candidiasis in the same AIDS patient.
J. Clin. Microbiol.
34:1542-1545[Abstract].
|
| 6.
|
Blumberg, H. M.,
E. F. Hendershot, and T. J. Lott.
1992.
Persistence of the same Candida albicans strain despite fluconazole therapy. Documentation by pulsed-field gel electrophoresis.
Diagn. Microbiol. Infect. Dis.
15:545-547[Medline].
|
| 7.
|
Christiansen, K. J.,
E. M. Bernard,
J. W. Gold, and D. Armstrong.
1985.
Distribution and activity of amphotericin B in humans.
J. Infect. Dis.
152:1037-1043[Medline].
|
| 8.
|
Collette, N.,
P. van der Auwera,
A. P. Lopez,
C. Heymans, and F. Meunier.
1989.
Tissue concentrations and bioactivity of amphotericin B in cancer patients treated with amphotericin B-deoxycholate.
Antimicrob. Agents Chemother.
33:362-368[Abstract/Free Full Text].
|
| 9.
|
Collette, N.,
P. van der Auwera,
F. Meunier,
C. Lambert,
J. P. Sculier, and A. Coune.
1991.
Tissue distribution and bioactivity of amphotericin B administered in liposomes to cancer patients.
J. Antimicrob. Chemother.
27:535-548[Abstract/Free Full Text].
|
| 10.
|
Conly, J.,
R. Rennie,
J. Johnson,
S. Farah, and L. Hellman.
1992.
Disseminated candidiasis due to amphotericin B-resistant Candida albicans.
J. Infect. Dis.
165:761-764[Medline]. (Comment.)
|
| 11.
|
Cormican, M. G., and M. A. Pfaller.
1995.
Epidemiology of candidiasis.
Compr. Ther.
21:653-657[Medline].
|
| 12.
|
Geber, A.,
C. A. Hitchcock,
J. E. Swartz,
F. S. Pullen,
K. E. Marsden,
K. J. Kwon-Chung, and J. E. Bennett.
1995.
Deletion of the Candida glabrata ERG3 and ERG11 genes: effect on cell viability, cell growth, sterol composition, and antifungal susceptibility.
Antimicrob. Agents Chemother.
39:2708-2717[Abstract].
|
| 13.
|
Ghannoum, M. A.,
Y. Fu,
A. S. Ibrahim,
L. A. Mortara,
M. C. Shafiq,
J. E. Edwards, Jr., and R. S. Criddle.
1995.
In vitro determination of optimal antifungal combinations against Cryptococcus neoformans and Candida albicans.
Antimicrob. Agents Chemother.
39:2459-2465[Abstract].
|
| 14.
|
Goetz, M. B.
1996.
Relationship between fluconazole dosage regimens and the emergence of fluconazole-resistant Candida albicans.
AIDS
10:335-336[Medline].
|
| 15.
|
Goff, D. A.,
S. L. Koletar,
W. J. Buesching,
J. Barnishan, and R. J. Fass.
1995.
Isolation of fluconazole-resistant Candida albicans from human immunodeficiency virus-negative patients never treated with azoles.
Clin. Infect. Dis.
20:77-83[Medline].
|
| 16.
|
Johnson, E. M.,
D. W. Warnock,
J. Luker,
S. R. Porter, and C. Scully.
1995.
Emergence of azole drug resistance in Candida species from HIV-infected patients receiving prolonged fluconazole therapy for oral candidosis.
J. Antimicrob. Chemother.
35:103-114[Abstract/Free Full Text].
|
| 17.
|
Kan, V. L.,
A. Geber, and J. E. Bennett.
1996.
Enhanced oxidative killing of azole-resistant Candida glabrata strains with ERG11 deletion.
Antimicrob. Agents Chemother.
40:1717-1719[Abstract].
|
| 18.
|
Kelly, S. L.,
D. C. Lamb,
D. E. Kelly,
J. Loeffler, and H. Einsele.
1996.
Resistance to fluconazole and amphotericin in Candida albicans from AIDS patients.
Lancet
348:1523-1524[Medline]. (Letter.)
|
| 19.
|
Kelly, S. L.,
D. C. Lamb,
D. E. Kelly,
N. J. Manning,
J. Loeffler,
H. Hebart,
U. Schumacher, and H. Einsele.
1997.
Resistance to fluconazole and cross-resistance to amphotericin B in Candida albicans from AIDS patients caused by defective sterol  5,6-desaturation.
FEBS Lett.
400:80-82[Medline].
|
| 20.
|
Lacassin, F.,
F. Damond,
C. Chochillon,
P. Longuet,
J. Lebras,
J. L. Vilde, and C. Leport.
1996.
Response to fluconazole by 23 patients with human immunodeficiency virus infection and oral candidiasis: pharmacological and mycological factors.
Antimicrob. Agents Chemother.
40:1961-1963[Abstract].
|
| 21.
|
Le Guennec, R.,
J. Reynes,
M. Mallie,
C. Pujol,
F. Janbon, and J. M. Bastide.
1995.
Fluconazole- and itraconazole-resistant Candida albicans strains from AIDS patients: multilocus enzyme electrophoresis analysis and antifungal susceptibilities.
J. Clin. Microbiol.
33:2732-2737[Abstract].
|
| 22.
|
Lewis, T. L.,
G. A. Keesler,
G. P. Fenner, and L. W. Parks.
1988.
Pleiotropic mutations in Saccharomyces cerevisiae affecting sterol uptake and metabolism.
Yeast
4:93-106[Medline].
|
| 23.
|
McCullough, M., and S. Hume.
1995.
A longitudinal study of the change in resistance patterns and genetic relationship of oral Candida albicans from HIV-infected patients.
J. Med. Vet. Mycol.
33:33-37[Medline].
|
| 24.
|
Nes, W.,
B. Sekula,
W. D. Nes, and J. Adler.
1978.
The functional importance of structural features of ergosterol in yeast.
J. Biol. Chem.
253:6218[Abstract/Free Full Text].
|
| 25.
|
Nguyen, M. H.,
C. J. Clancy,
V. L. Yu,
Y. C. Yu,
A. J. Morris,
D. R. Syndman,
D. A. Sutton, and M. G. Rinaldi.
1998.
Do in vitro susceptibility data predict the microbiologic response to amphotericin B? Results of a prospective study of patients with Candida fungemia.
J. Infect. Dis.
177:425-430[Medline].
|
| 26.
|
Odds, F. C., and R. Bernaerts.
1994.
CHROMagar Candida, a new differential isolation medium for presumptive identification of clinically important Candida species.
J. Clin. Microbiol.
32:1923-1929[Abstract/Free Full Text].
|
| 27.
|
Parks, L. W., and W. M. Casey.
1995.
Physiological implications of sterol biosynthesis in yeast.
Annu. Rev. Microbiol.
49:95-116[Medline].
|
| 28.
|
Pfaller, M., and J. Riley.
1992.
Effects of fluconazole on the sterol and carbohydrate composition of four species of Candida.
Eur. J. Clin. Microbiol. Infect. Dis.
11:152-156[Medline].
|
| 29.
|
Rex, J. H.,
C. R. Cooper, Jr.,
W. G. Merz,
J. N. Galgiani, and E. J. Anaissie.
1995.
Detection of amphotericin B-resistant Candida isolates in a broth-based system.
Antimicrob. Agents Chemother.
39:906-909[Abstract].
|
| 30.
|
Scheven, M., and C. Scheven.
1996.
Quantitative screening for fluconazole-amphotericin B antagonism in several Candida albicans strains by a comparative agar diffusion assay.
Mycoses
39:111-114[Medline].
|
| 31.
|
Scheven, M.,
C. Scheven,
K. Hahn, and A. Senf.
1995.
Post-antibiotic effect and post-expositional polyene antagonism of azole antifungal agents in Candida albicans: dependence on substance lipophilia.
Mycoses
38:435-442[Medline].
|
| 32.
|
Scheven, M., and F. Schwegler.
1995.
Antagonistic interactions between azoles and amphotericin B with yeasts depend on azole lipophilia for special test conditions in vitro.
Antimicrob. Agents Chemother.
39:1779-1783[Abstract].
|
| 33.
|
Steffan, P.,
J. A. Vazquez,
D. Boikov,
C. Xu,
J. D. Sobel, and R. A. Akins.
1997.
Identification of Candida species by randomly amplified polymorphic DNA fingerprinting of colony lysates.
J. Clin. Microbiol.
35:2031-2039[Abstract].
|
| 34.
|
Sterling, T. R.,
R. A. Gasser, Jr., and A. Ziegler.
1996.
Emergence of resistance to amphotericin B during therapy for Candida glabrata infection in an immunocompetent host.
Clin. Infect. Dis.
23:187-188[Medline].
|
| 35.
|
Valentin, A.,
R. Le Guennec,
E. Rodriguez,
J. Reynes,
M. Mallie, and J. M. Bastide.
1996.
Comparative resistance of Candida albicans clinical isolates to fluconazole and itraconazole in vitro and in vivo in a murine model.
Antimicrob. Agents Chemother.
40:1342-1345[Abstract].
|
| 36.
|
van Etten, E. W.,
M. Otte-Lambillion,
W. van Vianen,
M. T. ten Kate, and A. J. Bakker-Woudenberg.
1995.
Biodistribution of liposomal amphotericin B (AmBisome) and amphotericin B-desoxycholate (Fungizone) in uninfected immunocompetent mice and leucopenic mice infected with Candida albicans.
J. Antimicrob. Chemother.
35:509-519[Abstract/Free Full Text].
|
| 37.
|
Vazquez, J. A.,
M. T. Arganoza,
J. K. Vaishampayan, and R. A. Akins.
1996.
In vitro interaction between amphotericin B and azoles in Candida albicans.
Antimicrob. Agents Chemother.
40:2511-2516[Abstract].
|
| 38.
|
Wanger, A.,
K. Mills,
P. W. Nelson, and J. H. Rex.
1995.
Comparison of Etest and National Committee for Clinical Laboratory Standards broth macrodilution method for antifungal susceptibility testing: enhanced ability to detect amphotericin B-resistant Candida isolates.
Antimicrob. Agents Chemother.
39:2520-2522[Abstract].
|
| 39.
|
Wasan, K. M., and J. S. Conklin.
1996.
Evaluation of renal toxicity and antifungal activity of free and liposomal amphotericin B following a single intravenous dose to diabetic rats with systemic candidiasis.
Antimicrob. Agents Chemother.
40:1806-1810[Abstract].
|
Journal of Clinical Microbiology, September 1998, p. 2690-2695, Vol. 36, No. 9
0095-1137/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
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Abstract
Introduction
