Relationships between respiration and susceptibility to azole antifungals in Candida glabrata

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.     

Role of ATP-binding-cassette transporter genes in high-frequency acquisition of resistance to azole antifungals in Candida glabrata

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 microg/ml developed resistance to this agent and other azoles at a surprisingly high frequency (2 x 10(-4) to 4 x 10(-4)). We show here that this high-frequency azole resistance (HFAR) acquired in vitro was due, at least in part, to the upregulation of CgCDR1. The CgCDR1 deletion mutant DSY1041 could still develop HFAR but in a medium containing fluconazole at 5 microg/ml. In the HFAR strain derived from DSY1041, a distinct ABC transporter gene similar to CgCDR1, called CgCDR2, was upregulated. This gene was slightly expressed in clinical isolates but was upregulated in strains with the HFAR phenotype. Deletion of both CgCDR1 and CgCDR2 suppressed the development of HFAR in a medium containing fluconazole at 5 microg/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.     

Novel micelle formulations to increase cutaneous bioavailability of azole antifungals

Efficient topical drug administration for the treatment of superficial fungal infections would deliver the therapeutic agent to the target compartment and reduce the risk of systemic side effects. However, the physicochemical properties of the commonly used azole antifungals make their formulation a considerable challenge. The objective of the present investigation was to develop aqueous micelle solutions of clotrimazole (CLZ), econazole nitrate (ECZ) and fluconazole (FLZ) using novel amphiphilic methoxy-poly(ethylene glycol)-hexyl substituted polylactide (MPEG-hexPLA) block copolymers. The CLZ, ECZ and FLZ formulations were characterized with respect to drug loading and micelle size. The optimal drug formulation was selected for skin transport studies that were performed using full thickness porcine and human skin. Penetration pathways and micellar distribution in the skin were visualized using fluorescein loaded micelles and confocal laser scanning microscopy. The hydrodynamic diameters of the azole loaded micelles were between 70 and 165 nm and the corresponding number weighted diameters (d_n) were 30 to 40 nm. Somewhat surprisingly, the lowest loading efficiency (< 20%) was observed for CLZ (the most hydrophobic of the three azoles tested); in contrast, under the same conditions, ECZ was incorporated with an efficiency of 98.3% in MPEG-dihexPLA micelles. Based on the characterization data and preliminary transport experiments, ECZ loaded MPEG-dihexPLA micelles (concentration 1.3 mg/mL; d_n < 40 nm) were selected for further study. ECZ delivery was compared to that from Pevaryl® cream (1% w/w ECZ), a marketed liposomal formulation for topical application. ECZ deposition in porcine skin following 6 h application using the MPEG-dihexPLA micelles was > 13-fold higher than that from Pevaryl® cream (22.8 ± 3.8 and 1.7 ± 0.6 μg/cm², respectively). A significant enhancement was also observed with human skin; the amounts of ECZ deposited were 11.3 ± 1.6 and 1.5 ± 0.4 μg/cm², respectively (i.e., a 7.5-fold improvement in delivery). Confocal laser scanning microscopy images supported the hypothesis that the higher delivery observed in porcine skin was due to a larger contribution of the follicular penetration pathway. In conclusion, the significant increase in ECZ skin deposition achieved using the MPEG-dihexPLA micelles demonstrates their ability to improve cutaneous drug bioavailability; this may translate into improved clinical efficacy in vivo. Moreover, these micelle systems may also enable targeting of the hair follicle and this will be investigated in future studies.     

In-vitro resistance to imidazole antifungals in Candida albicans

Three strains of Candida albicans from patients with chronic mucocutaneous candidosis (CMC) who relapsed during prolonged treatment with ketoconazole were compared with three other Can. albicans strains by means of an agar incorporation MIC method, a broth microdilution method for IC30 determination, and a hyphal elongation assessment method. The MICs of ketoconazole, tioconazole and miconazole were difficult to interpret, but were much higher for the three CMC strains if low inoculum concentrations and short incubation times were used. The IC30S of the three imidazoles were much higher for the CMC strains than for the others. The imidazoles all caused minimal inhibition of hyphal elongation by the three CMC strains at concentrations up to 50 mg/l. Concentrations of 0.5 mg/l caused marked inhibition of the other strains.     

Decreased susceptibility of Candida albicans to azole antifungals: a complication of long-term treatment in autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) patients

BACKGROUND: Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED, APS1) is an autosomal recessive disease exceptionally common in Finland. Most patients have chronic oral candidiasis from early childhood and this infection has been shown to be carcinogenic. Hence, patients receive repeated treatment and prophylactic courses of antifungals throughout life. In Finland, 92 patients have been diagnosed with APECED and 66 of them are currently alive. Our aim was to study the effect of long-term azole treatment on the candidal colonization of APECED patients and the influence on antifungal susceptibilities. METHODS: We evaluated the culture reports from 1994 to 2004 of 56 APECED patients followed in Helsinki University Central Hospital. Candida albicans strains of all 11 patients initially reported resistant (n = 27) and 12 patients reported susceptible (n = 16) to fluconazole were re-analysed for their susceptibility to fluconazole. Antifungal usage was analysed up to 30 years back. RESULTS: A total of 162 fungal cultures had been performed. Of these, 75% had been reported positive for Candida and 63% for C. albicans. Eleven patients (31.4%) had been reported to harbour at least once a C. albicans strain resistant to fluconazole. Re-analysis of the stored C. albicans strains originally reported to be resistant to fluconazole revealed a mean MIC of 19.5 mg/L. CONCLUSIONS: Multiple courses (>6) of fluconazole annually and low dose prophylaxis are major risk factors for persistent colonization with C. albicans with decreased susceptibility in APECED patients.     

A new Aspergillus fumigatus resistance mechanism conferring in vitro cross-resistance to azole antifungals involves a combination of cyp51A alterations

Fourteen Aspergillus fumigatus clinical isolates that exhibited a pattern of reduced susceptibility to triazole drugs were analyzed. The sequences of the cyp51A gene from all isolates showed the presence of a point mutation at t364a, which led to the substitution of leucine 98 for histidine (L98H), together with the presence of two copies of a 34-bp sequence in tandem in the promoter of the cyp51A gene. Quantitative expression analysis (real-time PCR) showed up to an eightfold increase in the level of expression of the cyp51A gene compared to that by the susceptible strain. Three PCR fragments of one azole-resistant strain (strain CM2627) that included the promoter with the tandem repeat and part of cyp51A with the t364a mutation or PCR fragments with only one of the modifications were used to replace the cyp51A gene of an azole drug-susceptible A. fumigatus wild-type strain (strain CM237). Only transformants which had incorporated the tandem repeat in the promoter of the cyp51A gene and the L98H amino acid substitution exhibited similarly reduced patterns of susceptibility to all triazole agents and similarly increased levels of cyp51A expression, confirming that the combination of both alterations was responsible for the azole-resistant phenotype.     

Warfarin with fluoroquinolones, sulfonamides, or azole antifungals: interactions and the risk of hospitalization for gastrointestinal bleeding

The aim of this study was to determine whether a potential pharmacokinetic interaction between warfarin and orally administered anti-infectives increases the risk of hospitalization for gastrointestinal (GI) bleeding in warfarin users. We conducted a nested case-control and case-crossover study using US Medicaid data. Logistic regression was used to determine the association between GI bleeding and prior use of ciprofloxacin, levofloxacin, gatifloxacin, co-trimoxazole, or fluconazole vs. no exposure and also vs. use of cephalexin, which would not be expected to interact with warfarin. All of the anti-infectives examined were associated with elevated odds ratios (ORs) when compared to no exposure to these drugs. With cephalexin data as the reference, the ORs for co-trimoxazole (OR: 1.68 (95% confidence interval (CI): 1.21-2.33) in the prior 6-10 days) and fluconazole (OR: 2.09 (95% CI: 1.34-3.26) in the prior 11-15 days) were significantly elevated. Warfarin users who had received an anti-infective agent showed a substantially increased risk of GI bleeding. However, a drug-drug interaction with warfarin was evident only for co-trimoxazole and fluconazole.     

白色念珠菌对临床常用抗真菌药物的耐药性分析

目的了解白色念珠菌对临床常用抗真菌药物的耐药性。方法按照美国临床实验室标准化委员会（CLSI）推荐的酵母菌纸片扩散法敏感试验指南,对临床分离的494株白色念珠菌进行抗真菌药物的敏感性测定。结果 494株白色念珠菌对两性霉素B、制霉菌素敏感性最高,分别为96.1%和93.9%,对咪康唑的敏感性最低为51.9%;念珠菌常见临床感染部位为呼吸道,其次是泌尿道。白色念珠菌对唑类抗真菌药物存在较大的耐药性。结论白色念珠菌对常用抗真菌药物的耐药性呈上升趋势,其耐药机制有待于进一步研究。     

白念珠菌对唑类药物耐药机制的研究进展

白念珠菌是临床最常见的条件致病性真菌,由于抗真菌药物的长期滥用,其对唑类药物的耐药逐年增多,耐药现象已经成为药物治疗的难点。目前,白念珠菌对唑类药物耐药的主要机制包括:ERG11基因突变或过度表达导致的靶位酶的改变、多药转运蛋白过度表达、细胞应激反应和生物膜的形成等。现就白念珠菌对唑类药物的耐药机制作简单归纳。     

Effects of voriconazole on Candida glabrata in vitro.

The effects of voriconazole on the growth, morphology and lipids of Candida glabrata were studied. MIC data showed that voriconazole was up to 32- to 64-fold more active than fluconazole in its ability to inhibit various C. glabrata strains. Voriconazole inhibited the growth of C. glabrata in a dose-dependent fashion. Electron microscope examination showed that voriconazole treatment affected the external and internal morphology of C. glabrata. Treatment of C. glabrata with voriconazole inhibited ergosterol synthesis and led to accumulation of methylated sterols. In contrast, no significant difference in phospholipid composition was observed between treated and untreated cells.     

Mechanisms of azole resistance in petite mutants of Candida glabrata

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.     

Proteomic analysis of azole resistance in Candida albicans clinical isolates

Changes in protein expression within a matched set of Candida albicans isolates representing the acquisition of azole resistance were examined by two-dimensional polyacrylamide gel electrophoresis and peptide mass fingerprinting. Proteins differentially expressed in association with azole resistance included Grp2p, Ifd1p, Ifd4p, Ifd5p, and Erg10p, a protein involved in the ergosterol biosynthesis pathway.     

In vitro susceptibilities of zygomycetes to conventional and new antifungals

In vitro susceptibilities of 36 zygomycete isolates, belonging to six genera, to itraconazole, posaconazole, voriconazole, terbinafine, amphotericin B and 5-fluorocytosine were determined by using a broth microdilution adaptation of the National Committee for Clinical Laboratory Standards M-38P reference method. The influence of incubation time on MIC values, and the performance of a spectrophotometric method for MIC determination in comparison with the visual reference method, were also evaluated. Amphotericin B was active against most of the isolates. All the isolates were highly resistant to 5-fluorocytosine (MICs > 256 mg/L). Voriconazole was significantly less active than the other drugs with an overall MIC(90) (MIC at which 90% of the isolates were inhibited) of 32 mg/L. In contrast, posaconazole showed good activity (MIC(90) 1 mg/L). A wide range of MICs, from 0.03 to > or =32 mg/L, was obtained for itraconazole and terbinafine. Differences in susceptibility between and within genera were noted. Rhizopus spp. were significantly less susceptible to itraconazole, posaconazole, terbinafine and amphotericin B than Absidia spp., and less susceptible than Mucor spp. to amphotericin B. Terbinafine appeared to be more active against Rhizopus microsporus than against Rhizopus oryzae (geometric mean MIC of 0.15 and 64 mg/L, respectively). The activity of the drugs was dependent on the incubation period. A significant increase in MICs was noted between 24 and 48 h of incubation. On the other hand, the two methods used for MIC determination (visual and spectrophotometric readings) showed good agreement. These results suggest that the zygomycetes are a heterogeneous group for antifungal susceptibility. Some of the conventional and new antifungals are effective in vitro; their efficacies in vivo remain to be determined. The spectrophotometric method appears to be a valuable alternative to the visual method for MIC determination for zygomycetes.     

白念珠菌对唑类药物耐药机制中生物膜作用的研究进展

白念珠菌是人体最常见的机会性致病真菌。唑类药物广泛应用于临床以对抗白念珠菌感染,但白念珠菌对唑类药物的耐药现象越来越严重,作为其耐药机制的一个方面,生物膜的作用备受关注。我们主要介绍生物膜相关的研究进展。     

Effects of terconazole and other azole antifungal agents on the sterol and carbohydrate composition of Candida albicans

The effects of terconazole, a triazole antifungal, on the sterol and carbohydrate composition of Candida albicans was compared with that of three imidazoles: clotrimazole, miconazole, and butoconazole. Exposure of C. albicans to terconazole resulted in a profound depletion of ergosterol with a corresponding increase in lanosterol content versus control cells. Carbohydrate analysis revealed a significant (245%) increase in chitin and a minimal effect on glucan and mannan in terconazole-treated cells. Similar effects on sterol and carbohydrate composition were observed with clotrimazole and miconazole. Butoconazole had a similar effect on sterol composition but had no effect on carbohydrate composition. The decreased ergosterol and increased lanosterol content is consistent with 14 alpha-demethylase inhibition by terconazole and the other azoles. The increase in cell wall chitin is most likely due to deregulation of chitin synthesis secondary to ergosterol depletion in the cell membrane. Because both chitin and ergosterol are critical components of the fungal cell, perturbation of the production and localization of these components by terconazole is likely to contribute to the selective toxicity of this compound for C. albicans and other fungi.     

Species-specific differences in the susceptibilities of biofilms formed by Candida bloodstream isolates to echinocandin antifungals

The echinocandin susceptibilities of bloodstream Candida isolates growing in a biofilm was investigated. Within the therapeutic range of concentrations of each drug, caspofungin and micafungin were active against biofilms formed by Candida albicans or C. glabrata but not those formed by C. tropicalis or C. parapsilosis.