No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Doxorubicin selects for fluconazole-resistant petite mutants in Candida glabrata isolates
Abstract
Candida infections are a permanent threat to immunocompromised individuals such as cancer patients, and Candida glabrata has emerged as a major problem in recent years. Resistance may develop during lengthy antifungal therapies and is often mediated by upregulation of fungal drug efflux pumps. During chemotherapy the yeast cell is also exposed to cytotoxic agents that may affect its drug susceptibility. Four C. glabrata isolates, three susceptible and one resistant to fluconazole (FLU), were incubated with 20 μg/ml of doxorubicin (DOX) for 90 min. In a second experiment, the isolates were cultured with DOX for ten days. Samples were taken on subsequent days to determine the minimal inhibitory concentration (MIC) of FLU and to analyze expression of CgCDR1, CgCDR2, CgSNQ2 and CgPDR1. Samples were also used to assess the petite phenotype. Short-term DOX exposure did not induce efflux pump gene expression, but genes were consistently overexpressed in FLU-susceptible isolates during long-term exposure. An increase in MIC values on day 6 in two of the isolates coincided with the first occurrence of petite mutants in all susceptible isolates. The respiratory deficiency of selected petite mutants was confirmed by culturing mutants on agar containing glycerol as the sole carbon source. FLU MIC values for respiratory-deficient clones were ≥64 μg/ml, and efflux pump gene expression was greatly increased. The resistant isolate did not develop mitochondrial dysfunction. In summary, the cytotoxic agent DOX selects for FLU-resistant respiratory-deficient C. glabrata mutants, which may affect antifungal therapy.
... Of the 146 isolates, 24 (16). Of 11 caspofungin-resistant isolates that were available for repeat testing, 10 were also resistant to micafungin or anidulafungin. ...
... Moreover, in an analysis of molecular events leading to echinocandin resistance of C. glabrata isogenic isolates consecutively obtained from a patient receiving chronic TPN, a multidrug-resistant strain emerged after multiple courses of treatment with caspofungin but no previous azole exposure (8). Selective pressure from antifungal drugs, along with other factors, such as chemotherapy (24) and broad-spectrum antibacterial drugs (25), might lead to the expansion of similar phenotypes. ...
Cancer patients are at risk for candidemia, and increasing Candida spp. resistance poses an emerging threat. We determined rates of antifungal drug resistance, identified factors associated with resistance, and investigated the correlation between resistance and all-cause mortality rates among cancer patients with ≥1 C. glabrata-positive blood culture at MD Anderson Cancer Center, Houston, Texas, USA, during March 2005-September 2013. Of 146 isolates, 30 (20.5%) were resistant to fluconazole, 15 (10.3%) to caspofungin, and 10 (6.8%) to multiple drugs (9 caspofungin-resistant isolates were also resistant to fluconazole, 1 to amphotericin B). Independently associated with fluconazole resistance were azole preexposure, hematologic malignancy, and mechanical ventilation. Independently associated with caspofungin resistance were echinocandin preexposure, monocytopenia, and total parenteral nutrition. Fluconazole resistance was highly associated with caspofungin resistance, independent of prior azole or echinocandin use. Caspofungin resistance was associated with increased 28-day all-cause mortality rates. These findings highlight the need for good stewardship of antifungal drugs.
... 26,27 Furthermore, the mutagenic potential of DNA-altering chemotherapy on Candida species is also a concern that has not been adequately investigated. 28 In the current study, the vast majority of patients had recently received potent chemotherapy and were exposed to broad-spectrum antibiotics, precluding the identification of significant associations with resistance in the absence of a case -control study design. However, we found a significant clustering of triazole and caspofungin resistance, especially among C. glabrata isolates, which could reflect increased exposure to multiple antifungals. ...
Objectives:
The epidemiology and clinical course of candidaemia in patients with acute leukaemia, a population frequently exposed to antifungals, have not been extensively studied. In the present contemporary series of acute leukaemia patients, we describe patient characteristics, Candida species and MIC distributions and investigate the association between antifungal resistance and all-cause mortality.
Methods:
We performed a retrospective review of medical records and microbiological data of adult patients with acute leukaemia or high-risk myelodysplastic syndrome with at least one positive blood culture for Candida species at the MD Anderson Cancer Center between January 2008 and October 2012. Susceptibility was defined according to the 2012 epidemiological cut-off values and clinical breakpoints.
Results:
We identified 67 episodes of candidaemia in 65 patients. Almost all episodes (94%) occurred in patients who were receiving antifungal agents, 71% in patients receiving an echinocandin. Almost all isolates (99%) were of non-albicans Candida species [most frequently Candida parapsilosis (32%), Candida tropicalis (23%) and Candida glabrata (20%)]. Caspofungin non-susceptibility was significantly associated with fluconazole resistance (P < 0.001). Non-susceptibility to caspofungin and multidrug resistance were associated with excess 14 day [adjusted HR (aHR) 3.02 (95% CI 1.28-7.09), P = 0.011 and aHR 3.02 (95% CI 1.27-7.14), P = 0.012, respectively] and 30 day [aHR 2.96 (95% CI 1.38-6.37), P = 0.005 and aHR 2.86 (95% CI 1.31-6.21), P = 0.008, respectively] all-cause mortality.
Conclusions:
In patients with acute leukaemia, a shift in candidaemia epidemiology was noted with a 99% predominance of non-albicans species. Non-susceptibility of Candida strains to caspofungin or multidrug resistance were independent markers of poor outcome in this patient population.
Fluconazole in vitro susceptibility test results for 256,882 isolates of Candida spp. were collected from 142 sites in 41 countries from June 1997 to December 2007. Data were collected for 197,619 isolates
tested with voriconazole from 2001 to 2007. A total of 31 different species of Candida were isolated. Increased rates of isolation of the common non-albicans species C. glabrata (10.2% to 11.7%), C. tropicalis (5.4% to 8.0%), and C. parapsilosis (4.8% to 5.6%) were noted when the time periods 1997 to 2000 and 2005 to 2007 were compared. Investigators tested clinical
isolates of Candida spp. by the CLSI M44-A disk diffusion method. Overall, 90.2% of Candida isolates tested were susceptible (S) to fluconazole; however, 13 of 31 species identified exhibited decreased susceptibility
(<75% S), similar to that seen with the resistant (R) species C. glabrata and C. krusei. Among 197,619 isolates of Candida spp. tested against voriconazole, 95.0% were S and 3% were R. About 30% of fluconazole-R isolates of C. albicans, C. glabrata, C. tropicalis, C. rugosa, C. lipolytica, C. pelliculosa, C. apicola, C. haemulonii, C. humicola, C. lambica, and C. ciferrii remained S to voriconazole. An increase in fluconazole resistance over time was seen with C. parapsilosis, C. guilliermondii, C. lusitaniae, C. sake, and C. pelliculosa. Among the emerging fluconazole-R species were C. guilliermondii (11.4% R), C. inconspicua (53.2% R), C. rugosa (41.8% R), and C. norvegensis (40.7% R). The rates of isolation of C. rugosa, C. inconspicua, and C. norvegensis increased by 5- to 10-fold over the 10.5-year study period. C. guilliermondii and C. rugosa were most prominent in Latin America, whereas C. inconspicua and C. norvegensis were most common in Eastern European countries. This survey identifies several less-common species of Candida with decreased susceptibility to azoles. These organisms may pose a future threat to optimal antifungal therapy and underscore
the importance of prompt and accurate species identification and antifungal susceptibility testing.
Mitochondrial dysfunction is one of the possible mechanisms by which azole resistance can occur in Candida glabrata. Cells with mitochondrial DNA deficiency (so-called "petite mutants") upregulate ATP binding cassette (ABC) transporter genes and thus display increased resistance to azoles. Isolation of such C. glabrata mutants from patients receiving antifungal therapy or prophylaxis has been rarely reported. In this study, we characterized two sequential and related C. glabrata isolates recovered from the same patient undergoing azole therapy. The first isolate (BPY40) was azole susceptible (fluconazole MIC, 4 μg/ml), and the second (BPY41) was azole resistant (fluconazole MIC, >256 μg/ml). BPY41 exhibited mitochondrial dysfunction and upregulation of the ABC transporter genes C. glabrata CDR1 (CgCDR1), CgCDR2, and CgSNQ2. We next assessed whether mitochondrial dysfunction conferred a selective advantage during host infection by testing the virulence of BPY40 and BPY41 in mice. Surprisingly, even with in vitro growth deficiency compared to BPY40, BPY41 was more virulent (as judged by mortality and fungal tissue burden) than BPY40 in both systemic and vaginal murine infection models. The increased virulence of the petite mutant correlated with a drastic gain of fitness in mice compared to that of its parental isolate. To understand this unexpected feature, genome-wide changes in gene expression driven by the petite mutation were analyzed by use of microarrays during in vitro growth. Enrichment of specific biological processes (oxido-reductive metabolism and the stress response) was observed in BPY41, all of which was consistent with mitochondrial dysfunction. Finally, some genes involved in cell wall remodelling were upregulated in BPY41 compared to BPY40, which may partially explain the enhanced virulence of BPY41. In conclusion, this study shows for the first time that mitochondrial dysfunction selected in vivo under azole therapy, even if strongly affecting in vitro growth characteristics, can confer a selective advantage under host conditions, allowing the C. glabrata mutant to be more virulent than wild-type isolates.
Candida albicans is one of the most important opportunistic fungal pathogens. It can cause serious fungal diseases in immunocompromised patients,
including those with cancer. Treatment failures due to the emergence of drug-resistant C. albicans strains have become a serious clinical problem. Resistance incidents were often mediated by fungal efflux pumps which are
closely related to the human ABC transporter P-glycoprotein (P-gp). P-gp is often overexpressed in cancer cells and confers
resistance to many cytotoxic drugs. We examined whether cytotoxic drugs commonly used for cancer treatment (doxorubicin and
cyclophosphamide) could alter the expression of genes responsible for the development of fluconazole resistance in Candida cells in the way they can influence homologous genes in cancer cell lines. ABC transporters (CDR1 and CDR2) and other resistance genes (MDR1 and ERG11) were tested by real-time PCR for their expression in C. albicans cells at the mRNA level after induction by antineoplastic drugs. The results were confirmed by a lacZ gene reporter system
and verified at the protein level using GFP and immunoblotting. We showed that doxorubicin is a potent inducer of CDR1/CDR2 expression in C. albicans at both the mRNA and protein level and thus causes an increase in fluconazole MIC values. However, cyclophosphamide, which
is not a substrate of human P-gp, did not induce ABC transporter expression in C. albicans. Neither doxorubicin nor cyclophosphamide could influence the expression of the other resistance genes (MDR1 and ERG11). The induction of CDR1/CDR2 by doxorubicin in C. albicans and the resulting alteration of antifungal susceptibility might be of clinical relevance for the antifungal treatment of
Candida infections occurring after anticancer chemotherapy with doxorubicin.
Candida glabrata has been often isolated from AIDS patients with oropharyngeal candidiasis treated with azole antifungal agents, especially
fluconazole. We recently showed that the ATP-binding-cassette (ABC) transporter gene CgCDR1 was upregulated in C. glabrata clinical isolates resistant to azole antifungal agents (D. Sanglard, F. Ischer, D. Calabrese, P. A. Majcherczyk, and J. Bille,
Antimicrob. Agents Chemother. 43:2753–2765, 1999). Deletion of CgCDR1 in C. glabrata rendered the null mutant hypersusceptible to azole derivatives and showed the importance of this gene in mediating azole
resistance. We observed that wild-type C. glabrata exposed to fluconazole in a medium containing the drug at 50 μg/ml developed resistance to this agent and other azoles at
a surprisingly high frequency (2 × 10−4 to 4 × 10−4). We show here that this high-frequency azole resistance (HFAR) acquired in vitro was due, at least in part, to the upregulation
ofCgCDR1. The CgCDR1 deletion mutant DSY1041 could still develop HFAR but in a medium containing fluconazole at 5 μg/ml. In the HFAR strain derived
from DSY1041, a distinct ABC transporter gene similar to CgCDR1, calledCgCDR2, was upregulated. This gene was slightly expressed in clinical isolates but was upregulated in strains with the HFAR phenotype.
Deletion of both CgCDR1 and CgCDR2suppressed the development of HFAR in a medium containing fluconazole at 5 μg/ml, showing that both genes are important mediators
of resistance to azole derivatives in C. glabrata. We also show here that the HFAR phenomenon was linked to the loss of mitochondria in C. glabrata. Mitochondrial loss could be obtained by treatment with ethidium bromide and resulted in acquisition of resistance to azole
derivatives without previous exposure to these agents. Azole resistance obtained in vitro by HFAR or by agents stimulating
mitochondrial loss was at least linked to the upregulation of both CgCDR1 and CgCDR2.
Due to the global occurrence of multi-drug-resistant malarial parasites (Plasmodium falciparum), the anti-malarial drug most effective against malaria is artemisinin, a natural product (sesquiterpene lactone endoperoxide) extracted from sweet wormwood (Artemisia annua). However, artemisinin is in short supply and unaffordable to most malaria patients. Artemisinin can be semi-synthesized from its precursor artemisinic acid, which can be synthesized from simple sugars using microorganisms genetically engineered with genes from A. annua. In order to develop an industrially competent yeast strain, detailed analyses of microbial physiology and development of gene expression strategies are required.
Three plant genes coding for amorphadiene synthase, amorphadiene oxidase (AMO or CYP71AV1), and cytochrome P450 reductase, which in concert divert carbon flux from farnesyl diphosphate to artemisinic acid, were expressed from a single plasmid. The artemisinic acid production in the engineered yeast reached 250 microg mL(-1) in shake-flask cultures and 1 g L(-1) in bio-reactors with the use of Leu2d selection marker and appropriate medium formulation. When plasmid stability was measured, the yeast strain synthesizing amorphadiene alone maintained the plasmid in 84% of the cells, whereas the yeast strain synthesizing artemisinic acid showed poor plasmid stability. Inactivation of AMO by a point-mutation restored the high plasmid stability, indicating that the low plasmid stability is not caused by production of the AMO protein but by artemisinic acid synthesis or accumulation. Semi-quantitative reverse-transcriptase (RT)-PCR and quantitative real time-PCR consistently showed that pleiotropic drug resistance (PDR) genes, belonging to the family of ATP-Binding Cassette (ABC) transporter, were massively induced in the yeast strain producing artemisinic acid, relative to the yeast strain producing the hydrocarbon amorphadiene alone. Global transcriptional analysis by yeast microarray further demonstrated that the induction of drug-resistant genes such as ABC transporters and major facilitator superfamily (MSF) genes is the primary cellular stress-response; in addition, oxidative and osmotic stress responses were observed in the engineered yeast.
The data presented here suggest that the engineered yeast producing artemisinic acid suffers oxidative and drug-associated stresses. The use of plant-derived transporters and optimizing AMO activity may improve the yield of artemisinic acid production in the engineered yeast.
Two isolates of Candida glabrata from the same stool sample from a bone marrow transplant recipient treated with fluconazole, and designated 1084-L for large colonies on yeast extract-peptone-dextrose-agar and 1084-S for small colonies, were analysed. In-vitro susceptibility tests with a commercially available disk diffusion procedure showed that isolate 1084-L had a susceptibility pattern typical of wild-type strains of C. glabrata with sensitivity to polyenes and the presence of resistant colonies randomly distributed within the inhibition zones for all azole compounds except tioconazole. In contrast, isolate 1084-S, which was found by pulsed-field gel electrophoresis and random amplification of polymorphic DNA to be genetically closely related to isolate 1084-L, exhibited cross-resistance to the azole compounds except tioconazole. Determination of MICs by the E-test method confirmed these results, showing that isolate 1084-S had greater sensitivity to amphotericin B and complete resistance to ketoconazole and fluconazole. Growth on agar plates containing glucose or glycerol as the sole carbon source suggested that the resistant isolate had a respiratory deficiency, which was further demonstrated by flow cytometric analysis of the fluorescence of rhodamine 123-stained blastoconidia. Restriction endonuclease analysis of mitochondrial DNA (mtDNA) established the mitochondrial origin of the respiratory deficiency. However, PCR amplification of the mtDNA with primers ML1 and ML6, as well as transmission electron microscopy, suggested a partial deletion of the mtDNA analogous to that described for rho- petite mutants of Saccharomyces cerevisiae. Together, these results provided evidence that the selection of azole-resistant petite mutants of C. glabrata may occur in vivo after fluconazole administration, which might explain, therefore, clinical failure of antifungal therapy.
Since most nosocomial systemic yeast infections arise from the endogenous flora of the patient, we prospectively evaluated
the species stratification and antifungal susceptibility profile ofCandida spp. associated with heavy colonization and systemic infection in patients at Memorial Sloan-Kettering Cancer Center in New
York. A total of 349 Candida isolates were obtained from 223 patients during the later half of 1998. Cancer was the most common underlying disease, occurring
in 91% of the patients, including 61.8% with organ and 23.7% with hematological malignancies; 4.4% of the patients had AIDS.
Candida albicans was the predominant species (67.3%); among 114 non-albicans Candida spp., C. glabrata (45.6%) was the most frequent, followed by C. tropicalis (18.4%),C. parapsilosis (16.6%), and C. krusei(9.6%). The overall resistance to triazole-based agents among all yeast isolates was 9.4 and 10.8% for fluconazole and itraconazole,
respectively. A total of 5% of C. albicansstrains were resistant to triazole antifungals, whereas 30.8 and 46.2% of C. glabrata strains were resistant to fluconazole (MIC ≥ 64 μg/ml) and itraconazole (MIC ≥ 1 μg/ml), respectively. A significant association
was observed between prior treatment with triazole and isolation of fluconazole-resistant C. albicans (P = 0.005, OR 36), although this relationship was not seen in C. glabrata isolates (P = 0.4). This study reinforces the importance of periodic, prospective surveillance of clinical fungal isolates to determine
appropriate prophylactic, empiric, and preemptive antifungal therapy for the highly susceptible patient population.
Over the past two decades, the incidence of infections due to Candida glabrata, a yeast with intrinsic low susceptibility to azole antifungals, has increased markedly. Respiratory deficiency due to mutations in mitochondrial DNA (mtDNA) associated with resistance to azoles frequently occurs in vitro in this species. In order to specify the relationships between respiration and azole susceptibility, the effects of respiratory chain inhibitors on a wild-type isolate of C. glabrata were evaluated. Respiration of blastoconidia was immediately blocked after extemporaneous addition of potassium cyanide, whereas a 4-h preincubation was required for sodium azide. Antifungal susceptibility determined by a disk diffusion method on Casitone agar containing sodium azide showed a significant decrease in the susceptibility to azoles. Biweekly subculturing on Casitone agar supplemented with sodium azide was therefore performed. This resulted after 40 passages in the isolation of a respiration-deficient mutant, as suggested by its lack of growth on glycerol-containing agar. This respiratory deficiency was confirmed by flow cytometric analysis of blastoconidia stained with rhodamine 123 and by oxygraphy. Moreover, transmission electron microscopy and restriction endonuclease analysis of the mtDNA of mutant cells demonstrated the mitochondrial origin of the respiratory deficiency. Finally, this mutant exhibited cross-resistance to all the azoles tested. In conclusion, blockage of respiration in C. glabrata induces decreased susceptibility to azoles, culminating in azole resistance due to the deletion of mtDNA. This mechanism could explain the induction of petite mutations by azole antifungals which have been demonstrated to act directly on the mitochondrial respiratory chain.
We previously showed that resistant colonies of Candida glabrata inside the azole inhibition zones had respiratory deficiency due to mutations in mitochondrial DNA. Here, we analyzed the
mechanisms of azole resistance in petite mutants of C. glabrata obtained by exposure to fluconazole or induced by ethidium bromide. The respiratory deficiency of these mutants was confirmed
by oxygraphy and flow cytometric analysis with rhodamine 123, and its mitochondrial origin was demonstrated by transmission
electron microscopy and restriction endonuclease analysis of the mitochondrial DNA. Flow cytometry with rhodamine 6G suggested
an increased drug efflux in mutant cells, which was further supported by Northern blot analysis of the expression of the C. glabrata CDR1 (CgCDR1) and CgCDR2 genes, encoding efflux pumps. Conversely, the expression of CgERG11, which encodes the azole target, was not affected by petite mutations, and no differences were seen in the sequence of this
gene between parent isolates and mutants. Moreover, sterol analysis showed similar overall amount of sterols in parent and
mutant cells, but quantitative modifications were observed in the mutants, with almost undetectable biosynthesis intermediates.
Further analysis performed after separation of free sterols from steryl esters revealed a defect in sterol esterification
in mutant cells, with free ergosterol representing 92% of the overall sterol content. Thus, resistance or decreased susceptibility
to azoles in petite mutants of C. glabrata is associated with increased expression of CgCDR1 and, to a lesser extent, of CgCDR2. In addition, the marked increase in free ergosterol content would explain their increased susceptibility to polyenes.
The pathogenic yeast Candida glabrata exhibits innate resistance to fluconazole, the most commonly used antifungal agent. By screening a library of 9,216 random
insertion mutants, we identified a set of 27 genes which upon mutation, confer altered fluconazole susceptibility in C. glabrata. Homologues of three of these genes have been implicated in azole and/or drug resistance in Saccharomyces cerevisiae: two of these belong to the family of ABC transporters (PDR5 and PDR16), and one is involved in retrograde signaling from mitochondria to nucleus (RTG2). The remaining 24 genes are involved in diverse cellular functions, including ribosomal biogenesis and mitochondrial function,
activation of RNA polymerase II transcription, nuclear ubiquitin ligase function, cell wall biosynthesis, and calcium homeostasis.
We characterized two sets of mutants in more detail. Strains defective in a putative plasma membrane calcium channel (Cch1-Mid1)
were modestly more susceptible to fluconazole but showed a significant loss of viability upon prolonged fluconazole exposure,
suggesting that calcium signaling is required for survival of azole stress in C. glabrata. These mutants were defective in calcium uptake in response to fluconazole exposure. The combined results suggest that, in
the absence of Ca2+ signaling, fluconazole has a fungicidal rather than a fungistatic effect on C. glabrata. The second set of mutants characterized in detail were defective in mitochondrial assembly and organization, and these exhibited
very high levels of fluconazole resistance. Further analysis of these mutants indicated that in C. glabrata a mechanism exists for reversible loss of mitochondrial function that does not involve loss of mitochondrial genome and that
C. glabrata can switch between states of mitochondrial competence and incompetence in response to fluconazole exposure.
Given the ever increasing number of individuals at risk for fungal infections, it is imperative that physicians "think fungus" when evaluating a potentially infected patient. The list of documented fungal pathogens is extensive, and one can no longer ignore or dismiss fungi as contaminants or clinically insignificant when they are isolated from clinical material. It is also apparent that the prognosis and response to therapy may vary with the type of fungus causing the infection as well as with the immunological status of the host. The extended-spectrum triazoles and the echinocandins clearly expand the coverage available against opportunistic pathogens; however, several of the less common opportunists discussed herein are not susceptible to these newer agents. Thus, fungi with intrinsic resistance to even the very newest antifungal agents already exist in our environment and will surely emerge as opportunistic pathogens as these agents are used broadly in the high-risk patient groups. Both clinicians and microbiologists must become familiar with the various fungi, their epidemiologic and pathogenic features, and the optimal approaches to diagnosis and therapy.
Candida glabrata, a yeast with intrinsically low susceptibility to azoles, frequently develops increased azole resistance during prolonged
treatment. Transposon mutagenesis revealed that disruption of CgPDR1 resulted in an 8- to 16-fold increase in fluconazole susceptibility of C. glabrata. CgPDR1 is a homolog of Saccharomyces cerevisiae PDR1, which encodes a transcriptional regulator of multidrug transporters. Northern blot analyses indicated that CgPDR1 regulated both constitutive and drug-induced expression of CgCDR1, a multidrug transporter gene. In agreement with the Northern analysis, the Cgpdr1 mutant had increased rhodamine accumulation, in contrast to the decreased accumulation in the CgPDR1-overexpressing strain. Northern analyses also indicated the importance of CgPDR1 in fluconazole resistance arising during therapy. Two clinically resistant isolates had higher expression of CgPDR1 and CgCDR1 compared to their paired susceptible isolates. Integrative transformation of CgPDR1 from the two resistant isolates converted the Cgpdr1 mutant into azole-resistant strains with upregulated CgPDR1 expression. Two different amino acid substitutions, W297S in one isolate and F575L in the other, accounted for the upregulated
CgPDR1 expression and the resistance. Finally, CgPDR1 was shown to be required for the azole resistance due to mitochondrial deficiency. Thus, CgPDR1 encodes a transcriptional regulator of a pleiotropic drug resistance network and contributes to the azole resistance of clinical
isolates and petite mutants.
Invasive candidiasis (IC) is a leading cause of mycosis-associated mortality in the United States. We examined data from the National Center for Health Statistics and reviewed recent literature in order to update the epidemiology of IC. IC-associated mortality has remained stable, at approximately 0.4 deaths per 100,000 population, since 1997, while mortality associated with invasive aspergillosis has continued to decline. Candida albicans remains the predominant cause of IC, accounting for over half of all cases, but Candida glabrata has emerged as the second most common cause of IC in the United States, and several less common Candida species may be emerging, some of which can exhibit resistance to triazoles and/or amphotericin B. Crude and attributable rates of mortality due to IC remain unacceptably high and unchanged for the past 2 decades. Nonpharmacologic preventive strategies should be emphasized, including hand hygiene; appropriate use, placement, and care of central venous catheters; and prudent use of antimicrobial therapy. Given that delays in appropriate antifungal therapy are associated with increased mortality, improved use of early empirical, preemptive, and prophylactic therapies should also help reduce IC-associated mortality. Several studies have now identified important variables that can be used to predict risk of IC and to help guide preventive strategies such as antifungal prophylaxis and early empirical therapy. However, improved non-culture-based diagnostics are needed to expand the potential for preemptive (or early directed) therapy. Further research to improve diagnostic, preventive, and therapeutic strategies is necessary to reduce the considerable morbidity and mortality associated with IC.
Multidrug resistance (MDR) is a serious complication during treatment of opportunistic fungal infections that frequently afflict immunocompromised individuals, such as transplant recipients and cancer patients undergoing cytotoxic chemotherapy. Improved knowledge of the molecular pathways controlling MDR in pathogenic fungi should facilitate the development of novel therapies to combat these intransigent infections. MDR is often caused by upregulation of drug efflux pumps by members of the fungal zinc-cluster transcription-factor family (for example Pdr1p orthologues). However, the molecular mechanisms are poorly understood. Here we show that Pdr1p family members in Saccharomyces cerevisiae and the human pathogen Candida glabrata directly bind to structurally diverse drugs and xenobiotics, resulting in stimulated expression of drug efflux pumps and induction of MDR. Notably, this is mechanistically similar to regulation of MDR in vertebrates by the PXR nuclear receptor, revealing an unexpected functional analogy of fungal and metazoan regulators of MDR. We have also uncovered a critical and specific role of the Gal11p/MED15 subunit of the Mediator co-activator and its activator-targeted KIX domain in antifungal/xenobiotic-dependent regulation of MDR. This detailed mechanistic understanding of a fungal nuclear receptor-like gene regulatory pathway provides novel therapeutic targets for the treatment of multidrug-resistant fungal infections.
The effect of doxorubicin (DOX) on the fluconazole (FLU) susceptibility of C. dubliniensis was investigated. Isolates were exposed to DOX and FLU in a chequerboard assay and resistance gene expressions were analysed
after DOX exposure. The susceptibility of the yeast to FLU was decreased in the presence of DOX in the chequerboard assay
with FIC indices suggesting an antagonistic effect. Gene expression analyses showed an overexpression of CdCDR2. Hence, DOX was found to have an impact on resistance mechanisms in C. dubliniensis isolates.
The variation in Candida spp. causing bloodstream infection (BSI) and the frequency of resistance to fluconazole by patient age have been previously described. However, similar data have been shown for neither the echinocandins nor the newer triazoles. We analyzed the 24-h reference MIC data from the SENTRY Antimicrobial Surveillance Program to compare the antifungal resistance profiles and species distribution of Candida BSI isolates according to patient age. MIC results were obtained for anidulafungin, caspofungin, micafungin, fluconazole, posaconazole, and voriconazole, and recently revised Clinical and Laboratory Standards Institute breakpoints were applied. A total of 1239 Candida BSI isolates were obtained from 79 medical centers in 2008 to 2009: 50.0%, 17.4%, 17.4%, 9.8%, and 1.8% were Candida albicans (Ca), Candida glabrata (Cg), Candida parapsilosis (Cp), Candida tropicalis (Ct), and Candida krusei (Ck), respectively. Ca was most common in the 60- to 79-year age group (52.3%) and least common in the 80- to 99-year age group (46.7%), whereas Cg was most common in the 80- to 99-year age group (28.6%) and least common in the 0- to 19-year age group (2.0%). Cp and Ct were most common in the 0- to 19-year age group (28.5% and 12.9%, respectively), and Ck was most common among the patients in the 20- to 39-year age group (3.5%). No resistance to echinocandins was detected among isolates of Ca, Cp, and Ct from all age groups. Likewise, no resistance to posaconazole or voriconazole was observed in isolates of Ca, Cp, or Ck from all age groups. Resistance to both azoles and echinocandins was most prominent among isolates of Cg with the highest resistance rates to echinocandins (16.7%), fluconazole (16.7%), posaconazole (5.0%), and voriconazole (11.1%) among isolates from the 20- to 39-year age group. Both species distribution and antifungal resistance patterns vary markedly with patient age. Cg BSI isolates may show lower susceptibility rates to both azoles and echinocandins with the highest rates of resistance detected in 20- to 59-year-old patients.
Candida dubliniensis was first described in 1995 and is the most closely related species to the predominant human fungal pathogen Candida albicans. C. dubliniensis is significantly less prevalent and less pathogenic than C. albicans and is primarily associated with infections in HIV-infected individuals and other immunocompromised cohorts. The population structure of C. dubliniensis consists of three well-defined major clades and is significantly less diverse than C. albicans. The majority of C. dubliniensis isolates are susceptible to antifungal drugs commonly used to treat Candida infections. To date only two major patterns of antifungal drug resistance have been identified and the molecular mechanisms of these are very similar to the resistance mechanisms that have been described previously in C. albicans. However, significant differences are evident in the predominant antifungal drug mechanisms employed by C. dubliniensis, differences that reflect its more clonal nature, its lower prevalence and characteristics of its genome, the complete sequence of which has only recently been determined.
The resistance mechanisms to azole antifungal agents were investigated in this study with two pairs of Candida glabrata clinical isolates recovered from two separate AIDS patients. The two pairs each contained a fluconazole-susceptible isolate and a fluconazole-resistant isolate, the latter with cross-resistance to itraconazole and ketoconazole. Since the accumulation of fluconazole and of another unrelated substance, rhodamine 6G, was reduced in the azole-resistant isolates, enhanced drug efflux was considered as a possible resistance mechanism. The expression of multidrug efflux transporter genes was therefore examined in the azole-susceptible and azole-resistant yeast isolates. For this purpose, C. glabrata genes conferring resistance to azole antifungals were cloned in a Saccharomyces cerevisiae strain in which the ATP binding cassette (ABC) transporter gene PDR5 was deleted. Three different genes were recovered, and among them, only C. glabrata CDR1 (CgCDR1), a gene similar to the Candida albicans ABC transporter CDR genes, was upregulated by a factor of 5 to 8 in the azole-resistant isolates. A correlation between upregulation of this gene and azole resistance was thus established. The deletion of CgCDR1 in an azole-resistant C. glabrata clinical isolate rendered the resulting mutant (DSY1041) susceptible to azole derivatives as the azole-susceptible clinical parent, thus providing genetic evidence that a specific mechanism was involved in the azole resistance of a clinical isolate. When CgCDR1 obtained from an azole-susceptible isolate was reintroduced with the help of a centromeric vector in DSY1041, azole resistance was restored and thus suggested that a trans-acting mutation(s) could be made responsible for the increased expression of this ABC transporter gene in the azole-resistant strain. This study demonstrates for the first time the determinant role of an ABC transporter gene in the acquisition of resistance to azole antifungals by C. glabrata clinical isolates.
A microdilution transfer plate technique for determining in vitro synergy of antimicrobial agents is described. Combinations
of gentamicin-nalidixic acid against Proteus mirabilis and rifampin-amphotericin B against Candida albicans are used as examples to demonstrate the technique. Results correlate with published data obtained by conventional methods.
The technique is effective for evaluating the in vitro effects of antimicrobial agent combinations against both bacteria and
fungi. The technique enables one to produce a checkerboard gradient in a fast, convenient, and reproducible way; results are
easily visualized.
Adriamycin is adding significantly to the effects achieved with cancer chemotherapy. It is the purpose of this editorial to put this drug into current perspective. The following chapters are discussed: preclinical studies; clinical studies; toxicity; adriamycin analogues.
Saccharomyces cell uptake of Adriamycin and the ensuing cytotoxic response were found to be dependent upon the ionic strength of the medium used for drug treatment. A given concentration of Adriamycin which inhibited growth in complete medium ws found to be significantly cytotoxic when administered in water. Many survivors after Adriamycin treatment in water were found to be respiratory-deficient petite mutants containing mitochondrial deoxyribonucleic acid mutations. Petite mutants arising after Adriamycin treatment were not induced but selected from the preexisting population of spontaneously derived petite mutants (normal frequency, 2%) due to an increased resistance of these mutants to killing by Adriamycin as compared with normal respiratory-sufficient cells. The responses to Adriamycin in mitochondrial deoxyribonucleic acid respiratory-deficient mutants (rho-, rho degrees, mit-) with different impaired mitochondrial functions was studied. All were similarly more resistant to killing by Adriamycin than wild-type cells. The common deficiency shared by these mutants, i.e., nonfunctioning electron transport, may play a role in protecting these mutants from Adriamycin cytotoxicity. In addition, normal cells grown on glycerol, requiring aerobic respiration for carbon source utilization were more susceptible to killing by Adriamycin than cells grown on glucose. These studies suggest that a mitochndrial function in yeast may interact with Adriamycin to potentiate a cell cytotoxic mechanism of the drug.
We have investigated the effect of doxorubicin (Adriamycin) on the yeast Saccharomyces cerevisiae. Drug treatment was found to be cytotoxic to wild-type strains, in a concentration-dependent manner, whereas a petite mutant lacking the cytochrome oxidase (EC 1.9.3.1) subunit IV gene was resistant to doxorubicin. Transformation of the doxorubicin-resistant mutant with a yeast in vivo expression vector harboring the cytochrome oxidase subunit IV gene restored both respiration and sensitivity to doxorubicin. Another petite strain, with a mutation in the mitochondrial adenine nucleotide translocator (pet9), did not display doxorubicin resistance. However, in contrast to the subunit IV mutant, it possesses a functional respiratory chain. We also compared the cytotoxic effect of doxorubicin with those of daunorubicin and mitoxantrone in yeast. We found comparable levels of cytotoxicity for doxorubicin and daunorubicin, which were significantly greater than that for mitoxantrone. Finally, we constructed a yeast strain that overexpresses manganese superoxide dismutase (EC 1.15.1.1), an antioxidant enzyme present in mitochondria. Overexpression of manganese superoxide dismutase protected significantly against doxorubicin and daunorubicin cytotoxicity but only slightly against mitoxantrone cytotoxicity. Collectively, our results provide direct in vivo evidence that superoxide radicals participate in doxorubicin- and daunorubicin-induced cytotoxicity in yeast. Furthermore, these results indicate that mitochondrial respiration is a crucial factor in anthracycline, and perhaps mitoxantrone, cytotoxicity in yeast.
The toxicity of most drugs is associated with their enzymatic conversion to toxic metabolites. Bioactivation reactions occur in a range of cellular organs and organelles, including mitochondria. We have investigated different effects (i.e. growth inhibition, mortality and genotoxicity) of doxorubicin, epirubicin and mitoxantrone on the D7 strain of Saccharomyces cerevisiae and on its petite (rho degrees ) respiratory-deficient mutant at various cellular concentrations of cytochrome P450 and glutathione (GSH). The data confirmed the importance of oxygen production for doxorubicin toxicity. The complete absence, or a very low level, of cytochrome oxidase subunit IV conferred some resistance to doxorubicin. Low GSH levels decreased resistance to doxorubicin in both strains, suggesting that thiol depletion could potentiate membrane lipid peroxidation. Doxorubicin induction of petite colonies suggests that the drug is able to select rather than induce respiratory-deficient mutants. Epirubicin induced levels of cytotoxicity similar to those of doxorubicin. The effects did not appear to be significantly dependent on mitochondrial function or GSH levels, whereas cells were strongly protected by cytochrome P450. GSH did not induce an evident alteration. Neither were genotoxic effects induced. Mitoxantrone had reduced levels of both growth inhibition and cytotoxicity in comparison to anthracyclines and induced convertants, revertants and aberrants. All the effects considered were amplified at high cytochrome P450 cellular concentrations, although the drug was also shown to act without previous metabolism via cytochrome P450. Anthracenedione effectiveness was increased by metabolism via cytochrome P450 and partially reduced by GSH. However, further mechanisms were suggested, which might implicate mitochondrial function and/or production of electrophilic cytotoxic and/or genotoxic intermediates by means of GSH conjugation. The biological effectiveness of doxorubicin, epirubicin and mitoxantrone on S.cerevisiae was shown to be strictly dependent on cell-specific physiological/biochemical conditions, such as a functional respiratory chain and levels of cytochrome P450 and GSH.
After a talk on regulation of gene transcription in Candida albicans, a clinical mycologist was heard to ask: "What difference does all that make to the lady dying of disseminated Candida infection in her hospital bed?" The rapid expansion of research in fungal diseases is widening the communication gap between individuals with responsibility for patient care and those who study pathogenic fungi at the level of molecular biology. DNA-based technologies have produced real advances for patient care by delivering superior methods for fungus identification and strain typing that will soon find a routine place in patient management. Molecular research into the fine detail of the host-pathogen interplay in fungal disease has also made great advances, though the spin-offs to benefit the clinician are not yet obvious. Detection of fungal DNA as a non-culture diagnostic method still requires considerable refinement before it can be regarded as a routinely useful approach, and genomic-based strategies for discovery of novel antifungal drugs from molecular targets have so far produced no agents that have entered development. It is inevitable that, in time, several aspects of molecular mycology research will become important basic knowledge for the clinician who is treating the patient. Therefore, clinicians and bench scientists with specialist interest in mycoses need to retain a reasonable level of mutual comprehension and respect of each other's work rather than assuming their professional paths are divergent.
A systematic investigation covering a wide diversity of yeast species was made on the appearance of respiratory deficient (petite) mutants after treatment with acriflavine. Petite mutants were obtained from certain species only, but in these species all strains were found to have in common the property of giving rise to petite mutants; such species were designated as “petite positive”. Species failing to give rise to petite mutants were accordingly called “petite negative”. The primary action of acriflavine, namely the inhibition of the synthesis of the respiratory system, was shown to occur not only in petite positive yeasts, but also in petite negative ones. Some implications of the results are discussed.
Objective:
Patients with diabetes mellitus are at increased risk of vulvovaginal candidiasis (VVC). Besides Candida albicans, they often have infection due to non-C. albicans Candida species such as C. glabrata. Oral single dose fluconazole (150 mg) is commonly used to treat VVC in non-diabetic individuals with response rate varying from 70 to 90%. However, there is paucity of related information in diabetic women with VVC. Present study has been conducted to systematically assess the effect of fluconazole therapy among diabetic patients with clinically symptomatic VVC.
Methods:
Study subjects included 85 consecutive patients with diabetes mellitus (type 2=70 and type 1=15) and 62 non-diabetic women who had clinical signs and symptoms of VVC and in whom evidence of candidiasis was documented by presence of yeast on direct microscopy followed by culture. Single dose fluconazole (150 mg) was given orally to all the subjects in a supervised manner. Subjects were reassessed on 14th day after fluconazole therapy and a repeat high vaginal swab was taken for direct microscopy and fungal culture. Total glycosylated haemoglobin (HbA1) was measured to assess glycaemic control.
Results:
There were no significant differences in the frequency of pruritus (55.9 vs. 56.7%), vaginal discharge (63.8 vs. 69.0%), dyspareunia (25.0 vs. 20.0%), and percentage yeast positivity (67.5 vs. 54.7%) between diabetic and control groups before the start of fluconazole therapy. Following fluconazole therapy, vaginal discharge on examination and yeast positivity on direct microscopy continued to remain positive in higher percentage of subjects in the diabetic group as compared to non-diabetic subjects (52.5 vs. 36.4%; P =0.22 and 50.7 and 29.0%, respectively, P =0.07, respectively). Overall 67.1% of patients with diabetes and 47.3% of controls continued to show persistence of Candida growth on high vaginal swab culture following fluconazole treatment (P=0.042). Candida glabtara was the most common species isolated in patients with diabetes mellitus and its frequency was significantly higher in them when compared to control group (54.1 vs. 22.6%, P<0.001). C. albicans was the most common species isolated in controls. Species-specific response to fluconazole showed that 81.3% of patients in the diabetic group and 78.6% of the non-diabetic controls continued to show fungal growth when C. glabrata was the organism grown (P=0.99). However, in case of C. albicans, 45.4% of the patients in the diabetic group and only 21.5% of the controls had persistent Candida growth following fluconazole therapy (P=0.22).
Conclusion:
Overall only one third of patients with diabetes mellitus and VVC respond to single dose 150 mg of fluconozole therapy. Limited response in the clinical symptoms and culture negativity following single dose fluconazole therapy in diabetic subjects with VVC is explained by the high prevalence of C. glabrata in them. The present study involved only 85 patients and majority of them had type-2 diabetes mellitus. There is need to perform similar study in large number of diabetics subjects including patients with type-1 diabetes mellitus and assess various alternative treatment protocol which are also effective in C. glabrata infection.
The epidemiology of invasive fungal infection is evolving. Yeasts other than Candida albicans and molds other than Aspergillus fumigatus have emerged as significant causes of invasive mycoses in severely immunocompromised patients. Although, in some instances,
these changes may be related to medical interventions, such as the use of antifungal agents in prophylaxis, in the majority
of cases, they seem to be a consequence of changes in the host, such as more-severe immunosuppression or different types of
immunosuppression impacting both risk periods and the infections that occur. These factors have altered the epidemiology of
infection in organ transplant recipients, premature newborns, and critically ill patients. This review discusses the epidemiology
of some fungal infections that have emerged in the past few years, with an emphasis on the potential factors associated with
their emergence and on practical implications of these epidemiological changes.
Opportunistic fungal infections are major causes of morbidity and mortality among immunocompromised individuals. Fungi have
evolved complex and coordinated mechanisms to survive in the environment and in the mammalian host. Fungi must adapt to “stressors”
in the host (including scarcity of nutrients, pH, and reactive oxygen and nitrogen intermediates) in addition to evading host
immunity. Knowledge of the immunopathogenesis of fungal infections has paved the way to promising strategies for immunotherapy.
These include strategies that increase phagocyte number, activate innate host defense pathways in phagocytes and dendritic
cells, and stimulate antigen-specific immunity (e.g., vaccines). Immunotherapy must be tailored to specific immunocompromised
states. Challenges exist in bringing promising immunotherapies from the laboratory to clinical trials.
Candida albicans is an important opportunistic pathogen that can cause serious fungal diseases in immunocompromised patients including cancer patients, transplant patients, and patients receiving immunosuppressive therapy in general, those with human immunodeficiency virus infections and undergoing major surgery. Its emergence spectrum varies from mucosal to systemic infections and the first line treatment is still based on fluconazole, a triazole derivate with a potent antifungal activity against most of C. albicans strains. Nevertheless the emergence of fluconazole-resistant C. albicans strains can lead to treatment failures and thus become a clinical problem in the management of such infections. For that reason we consider it important to study mechanisms inducing azole resistance and the possibilities to influence this process. In this work we give a short report on a real-time PCR (TaqMan) assay, which can be used for quantitative analyses of gene expression levels of MDR1, CDR1 and ERG11, genes supposed to contribute to development of the resistance mechanisms. We show some results achieved with that assay in fluconazole susceptible and resistant strains that confirm results seen earlier in experiments using Northern blot hybridisation and prove that the comparative DeltaCt method is valid for our system.
Statins are widely used for lowering cholesterol levels through their action on 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase. Yeasts use HMG-CoA reductase for the same enzymatic step as humans, but in yeasts the main end-product of the pathway is ergosterol rather than cholesterol. We considered that insights into the effects of statins in humans could be gained by examination of the effects of simvastatin on the petite-positive yeast Candida glabrata. Simvastatin was found to inhibit growth, and this was associated with lower ergosterol levels. As simvastatin-treated cultures of yeast were passaged, the frequencies of petite cells (respiratory-deficient yeast mutants with deletions in the mitochondrial genome) increased with time and with simvastatin concentration. DNA staining of the petite mutants showed that they were devoid of mtDNA, suggesting a defect in the maintenance of mtDNA. These observations in C. glabrata may provide further insights into the molecular effects of statins in humans undergoing treatment for hypercholesterolemia. In addition, if C. glabrata is a valid model for studying statin treatments, it would be very useful for the preliminary screening of agents to reduce statin side-effects.
Our previous investigation on Candida glabrata azole-resistant isolates identified two isolates with unaltered expression of CgCDR1/CgCDR2, but with upregulation of another ATP-binding cassette transporter, CgSNQ2, which is a gene highly similar to ScSNQ2 from Saccharomyces cerevisiae. One of the two isolates (BPY55) was used here to elucidate this phenomenon. Disruption of CgSNQ2 in BPY55 decreased azole resistance, whereas reintroduction of the gene in a CgSNQ2 deletion mutant fully reversed this effect. Expression of CgSNQ2 in a S. cerevisiae strain lacking PDR5 mediated not only resistance to azoles but also to 4-nitroquinoline N-oxide, which is a ScSNQ2-specific substrate. A putative gain-of-function mutation, P822L, was identified in CgPDR1 from BPY55. Disruption of CgPDR1 in BPY55 conferred enhanced azole susceptibility and eliminated CgSNQ2 expression, whereas introduction of the mutated allele in a susceptible strain where CgPDR1 had been disrupted conferred azole resistance and CgSNQ2 upregulation, indicating that CgSNQ2 was controlled by CgPDR1. Finally, CgSNQ2 was shown to be involved in the in vivo response to fluconazole. Together, our data first demonstrate that CgSNQ2 contributes to the development of CgPDR1-dependent azole resistance in C. glabrata. The overlapping in function and regulation between CgSNQ2 and ScSNQ2 further highlight the relationship between S. cerevisiae and C. glabrata.