Human salivary histatin 5 fungicidal action does not induce programmed cell death pathways in Candida albicans

Salivary histatins (Hsts) are potent candidacidal proteins that induce a nonlytic form of cell death in Candida albicans accompanied by loss of mean cell volume, cell cycle arrest, and elevation of intracellular levels of reactive oxygen species (ROS). Since these phenotypes are often markers of programmed cell death and apoptosis, we investigated whether other classical markers of apoptosis, including generation of intracellular ROS and protein carbonyl groups, chromosomal fragmentation (laddering), and cytochrome c release, are found in Hst 5-mediated cell death. Increased intracellular levels of ROS in C. albicans were detected in cells both following exogenous application of Hst 5 and following intracellular expression of Hst 5. However, Western blot analysis failed to detect specifically increased protein carbonylation in Hst 5-treated cells. There was no evidence of chromosomal laddering and no cytochrome c release was observed following treatment of C. albicans mitochondria with Hst 5. Superoxide dismutase enzymes of C. albicans and Saccharomyces cerevisiae provide essential protection against oxidative stress; therefore, we tested whether SOD mutants have increased susceptibility to Hst 5, as expected if ROS mediate fungicidal effects. Cell survival of S. cerevisiae SOD1/SOD2 mutants and C. albicans SOD1 mutants following Hst 5 treatment (31 micro M) was indistinguishable from the survival of wild-type cells treated with Hst 5. We conclude that ROS may not play a direct role in fungicidal activity and that Hst 5 does not initiate apoptosis or programmed cell death pathways.     

The influence of 5-fluorocytosine on nucleic acid synthesis in Candida albicans, Cryptococcus neoformans, and Aspergillus fumigatus.

5-Fluorocytosine (5-FC) has a rapid inhibitory effect on the synthesis of RNA and DNA in the yeast and hyphal form of Candida albicans. 5-FC has a less marked effect on the RNA and DNA content of sensitive strains of Cryptococcus neoformans and has no effect on the nucleic acid content of Aspergillus fumigatus nor of resistant strains of C. albicans and C. neoformans. 5-FC has a slower inhibitory effect on yeast cell number increase and no effect on hyphal length of hyphal phase C. albicans over a 7-h incubation period. Rapidly growing yeasts of C. albicans and C. neoformans decrease in volume and in dry weight per cell. 5-FC prevents this decrease in sensitive strains. These results have been discussed with respect to the known metabolic pathway of 5-FC, the fungistatic and fungicidal action of 5-FC and the development of resistance to 5-FC.     

Antagonistic effects of fluconazole and 5-fluorocytosine on candidacidal action of amphotericin B in human serum.

This study addressed the effects of fluconazole and 5-fluorocytosine on the candidacidal activity of amphotericin B in the presence of human serum. A Candida albicans isolate that was susceptible to all three agents according to standard testing procedures was employed. Fungicidal activity was estimated by using a flow cytometric procedure that exploited the fact that yeast cells killed by amphotericin B diminish in size and take up propidium iodide. The following findings were made. (i) Fluconazole and 5-fluorocytosine each failed to inhibit pseudohyphal formation and cell aggregation even when applied at 10 and 50 micrograms/ml, respectively, for up to 10 h. Hence, these agents were not fungistatic when tested in the presence of serum. (ii) Simultaneous application of 5-fluorocytosine had neither enhancing nor inhibitory effects on the fungicidal activity of amphotericin B. However, yeasts that were preincubated for 20 h with 5-fluorocytosine became less susceptible to killing by amphotericin B. (iii) Fluconazole exerted a frank antagonistic effect on the fungicidal activity of amphotericin B. Thus, under our in vitro conditions, both fluconazole and 5-fluorocytosine can overtly antagonize the candidacidal action of amphotericin B.     

Anticandidal activities of terconazole, a broad-spectrum antimycotic.

Terconazole is a new triazole ketal derivative with broad-spectrum in vitro and in vivo antifungal activities. This study further characterizes the effects of terconazole in vitro on yeast cell growth, viability, and morphology. Terconazole inhibited the growth of Candida albicans ATCC 44859 in a concentration-related manner, but with modest effects noted at levels from 10(-8) to 10(-5) M when the yeast was grown on media favoring the cell form. The inhibitory potency of terconazole on yeast cell viability varied with the strain and species of Candida tested. The susceptibility of C. albicans ATCC 44859 to terconazole was markedly enhanced when the yeast was grown on Eagle minimum essential medium, which favors mycelium formation. The effects of terconazole on the morphology of yeast cells (grown on Eagle minimum essential medium) were shown by phase-contrast and electron microscopy. There is a progression of changes, from loss of mycelia formation at 10(-8) M terconazole through complete necrosis at 10(-4) M.     

In vitro susceptibility of 245 yeast isolates to amphotericin B, 5-fluorocytosine, ketoconazole, fluconazole and itraconazole.

The in vitro activity of amphotericin B, 5-fluorocytosine, ketoconazole, fluconazole and itraconazole was tested against 245 yeast strains isolated from clinical specimens (68 Candida albicans, 74 Candida tropicalis, 43 Candida krusei, 28 Candida glabrata, 19 Candida parapsilosis, 8 Candida lusitaniae and 5 Candida guilliermondii). An agar dilution method was employed to carry out testing. Minimal inhibitory concentrations to restrain 90% of isolate growth (MIC90) ranged from 0.12 to 2 mg/l for amphotericin B and for 5-fluorocytosine, from 0.03 to 8 mg/l for ketoconazole, from 0.05 to 50 mg/l for itraconazole and from 0.1 to > 100 mg/l for fluconazole. Among the azole derivatives, the most active was ketoconazole, followed by itraconazole. Only 1 strain of C. albicans was resistant to amphotericin B (MIC > 4 mg/l). Both C. tropicalis and C. krusei responded poorly to fluconazole and the former to itraconazole as well. The species most susceptible to the antifungal agents tested was C. glabrata and the most resistant were C. tropicalis and C. krusei.     

The postantifungal effect of 5-fluorocytosine on Candida albicans.

The in-vitro postantifungal effect (PAFE) of 5-fluorocytosine for Candida albicans for short periods of time was investigated. Yeast cells were exposed for 0.5, 1 or 2 h to a range of concentrations (0.1-3.2 mg/L) of 5-fluorocytosine. The PAFE was quantitated by determinations of the number of colony forming units at hourly intervals (0-10 h) after removal of the drug by dilution. The length of the PAFE was dependent upon the concentration of 5-fluorocytosine and the duration of exposure. An exposure time of 0.5 h resulted in PAFE's ranging from 0 to 4.2 h. Exposure times of 1 and 2 h resulted in longer PAFEs and in many instances suppression of cell growth was seen for the entire evaluation period (up to ten hours).     

Mechanisms of action of 5-fluorocytosine.

5-Fluorouracil and 5-fluorodeoxyuridine monophosphate levels were estimated in 75 isolates of Candida albicans to determine whether 5-fluorocytosine susceptibility could be ideally correlated with the intrafungal formation of both 5-fluorodeoxyuridine monophosphate and 5-fluorouridine triphosphate or a reciprocal formation of the two metabolites to prove the mechanism of 5-fluorocytosine activity. Using the results of four in vitro susceptibility tests, we separated isolates of C. albicans into susceptibility groups. For most strains, there was a positive correlation between the degree of 5-fluorocytosine susceptibility and the inhibition of biosynthesis of both RNA and DNA, incorporation of 5-fluorouracil into RNA, inhibition of ribosomal protein synthesis, and levels of 5-fluorodeoxyuridine monophosphate. However, in some strains with a similar degree of 5-fluorocytosine resistance, either reduced incorporation of 5-fluorouracil or reduced 5-fluorodeoxyuridine monophosphate levels occurred, suggesting that these two mechanisms are not necessarily linked to each other and that both may be responsible for 5-fluorocytosine activity.     

Rapid Microdilution-Colorimetric Assay for Yeast Susceptibility to Fluorocytosine

Acid production by certain yeast species through the fermentation of glucose was used as the basis of an in vitro test for measuring susceptibility of these organisms to 5-fluorocytosine. Serial dilutions of 5-fluorocytosine in yeast nitrogen base broth, with bromothymol blue indicator dye, were made on microtiter plates. A fixed-concentration suspension of yeast cells was added to successive wells of the plates, and the color change from blue to yellow, indicating generation of acid, was noted. Eighteen hours after inoculation the lowest concentration of 5-fluorocytosine that completely inhibited the production of acid was recorded as the minimum inhibitory concentration. The results were reproducible in multiple trials with organisms of the genera Candida, Torulopsis, and Saccharomyces. This test is a rapid, inexpensive alternative to current 48- to 72-h methods in which broth turbidity is used as the end point.     

儿科患者中真菌分布及耐药监测

目的了解我院2000-2006年临床深部真菌感染分离的病原真菌种类及对抗真菌药物的耐药性变化。方法分析2000年1月～2006年12月年我院住院患儿所有送检真菌培养标本中分离出的菌株，药敏试验使用ATB-FUNGUS2INT酵母药敏试条，进行5-氟胞嘧啶、氟康唑和两性霉素B3种抗真菌药敏检测，严格按照2006年CLSIM27-A2规则及标准进行。结果分离出635株真菌中，念珠菌属572株（90．1％），曲霉属29株（4．6％），隐球菌属21株（3．3％），青霉属和酵母属各5株（0．8％），毛孢菌属2株（0．3％），毛霉属1株（0．2％）。念珠菌属中，前3位分离菌是白念珠菌418株（73．1％）；光滑念珠菌64株（11．2％）；热带念珠菌52株（9．1％）。白念珠菌对5-氟胞嘧啶、氟康唑和两性霉素B敏感率分别为97．6％，97．6％和98．4％。结论儿科患者中分离的真菌中以念珠菌属最多，并以白念珠菌为主，曲霉比率也在增多。5-氟胞嘧啶、氟康唑和两性霉素B均有较高的抗真菌活性。应加强真菌分离鉴定和耐药性监测，供合理选用抗真菌药物的参考。     

白念珠菌14-α脱甲基酶K143Q氨基酸置换与氟康唑耐药形成的相关性研究

目的研究临床耐氟康唑白念珠菌14-α脱甲基酶的K143Q氨基酸置换与氟康唑耐药形成的关系。方法运用体外定点突变技术构建ERG11基因A427C突变型重组质粒,并利用酶切、连接构建YES2/CT酵母表达质粒。通过构建成的表达质粒在酿酒酵母中的异源性表达及体外药物敏感性表型的检测,分析其致K143Q氨基酸置换与白念珠菌对氟康唑产生耐药的关系。结果真菌体外药物敏感性表型检测显示,含氨基酸置换的表达质粒转染于酿酒酵母INVSc1后,氟康唑最低抑菌浓度(MIC)增加16倍。结论 K143Q可增强白念珠菌对氟康唑的耐药性。     

Effect of an arginine-glycine-aspartic acid-containing peptide on hematogenous candidal infections in rabbits.

The adherence of Candida albicans yeast cells to the subendothelial extracellular matrix, fibronectin, laminin, and type I and IV collagen was tested. Fibronectin (10(-7) M) and a peptide, PepTite-2000 (Telios Pharmaceuticals Inc., San Diego, Calif.), containing the sequence arginine-glycine-aspartic acid (RGD) inhibited Candida adherence to these targets by greater than 90%. When C. albicans was perfused over ex vivo rabbit aortic endothelium, there was no significant difference in the amount of adherence in the presence or absence of the RGD-containing peptide. However, the RGD-containing peptide reduced the number of Candida organisms present in liver, brain, heart, and kidneys (P less than 0.05) of rabbits 4 h after intravenous inoculation of 5 x 10(7) C. albicans yeast cells. The peptide also reduced the number of macroscopic Candida abscesses in the kidneys of rabbits 72 h after intravenous inoculation of 10(7) C. albicans yeast cells (P less than 0.05). Inhibition of Candida adherence in vitro and in vivo may occur because the peptide blocks a fungal receptor that is necessary for adherence.     

307株念珠菌属分布及耐药性分析

目的研究我院临床分离的真菌特点及耐药情况。方法对临床分离的真菌，用CHROMagar显色培养基及VITEK-32YBC卡鉴定菌种，统计检出率和菌种分布，用ATB-Fungus药敏卡测试。结果白念珠菌检出率最高，占67．8％；分离的菌株对制霉菌素、两性霉素B和5-氟胞嘧啶敏感率最高，分别为94．2％，90．5％和89．2％；对酮康唑、益康唑敏感率较低。结论临床分离的念珠菌感染以白念珠菌、热带念珠菌、光滑念珠菌为主，制霉菌素、两性霉素B有较好的体外抗菌活性，是治疗该菌感染的有效药物。     

The use of Niger seed agar to screen for Candida dubliniensis in the clinical microbiology laboratory

Candida dubliniensis is a recently described pathogenic yeast that is closely related to C. albicans. The germ tube test is used routinely in diagnostic laboratories for the identification of C. albicans, and C. dubliniensis may also produce germ tubes under the same conditions. We evaluated a previously described method for differentiating between the two species using Niger seed agar (Staib agar). The aim was to find a useful, user-friendly and cost-effective method for use in diagnostic work. C. albicans produces only yeast cells on this medium after 24 h at 37 degrees C, while C. dubliniensis produces extensive hyphal and pseudohyphal growth that is easily observed. Of 495 yeasts isolated in, or sent for identification to, a diagnostic mycology laboratory 9 isolates (1.8%) were found to be C. dubliniensis. The method was found to be valuable for screening yeasts before proceeding to further identification if positive for hyphal/pseudohyphal growth on Niger seed agar. This method is therefore suitable for the screening of selected yeast isolates in order to identity C. dubliniensis and will further our understanding of the clinical importance of this species.     

Fluconazole in the treatment of Candida-associated denture stomatitis.

A double-blind trial was carried out to study the effect of oral administration of fluconazole in the treatment of Candida-associated denture stomatitis. The study group consisted of 38 denture stomatitis patients who harbored yeasts, predominantly Candida spp., in significant numbers as determined by culture from the lesions. Half of the patients received 50 mg of fluconazole per day orally for 14 days, and the other half received placebo capsules. The following parameters were studied: degree of palatal erythema, presence of yeast cells (by plate count and microscopy of smears), identification to the species level of dominant yeast organisms, biotyping of Candida albicans, and treatment-related side effects. A significant reduction of erythema was seen after treatment with fluconazole, but the inflammation showed partial relapse 2 to 4 weeks after treatment was terminated. Reduced soreness of the oral mucosa was reported by six of the patients in the fluconazole group. No significant clinical or yeast flora changes were observed in the placebo group. Extensive changes in the yeast flora were observed in the fluconazole group, both in quantity and in composition of yeast species and C. albicans strains (biotypes), which perhaps indicated differences in pathogenicity and fluconazole susceptibility among various yeast species and C. albicans strains. Fluconazole did not produce any changes in the results of blood and urine analyses. The results indicate that fluconazole is a safe and well-tolerated antimycotic drug. The transient clinical and antimycotic effect may have been due in part to the possibility that therapeutic concentrations of the drug were not reached beneath the fitting denture surface and within the denture plaque.     

YCD/5-FC自杀基因治疗系统对K562B白血病细胞杀伤作用的小鼠体内实验研究

目的　了解酵母菌胞嘧啶脱氨酶 5 氟胞嘧啶 (YCD 5 FC)系统在体内对转基因高致瘤性K5 6 2细胞 (K5 6 2B细胞 )的杀伤效应。方法　以高滴度逆转录病毒转染K5 6 2B细胞并筛选出阳性转染克隆YCD K5 6 2B ;12只SCID小鼠分为治疗及对照组 ,在小鼠左右两侧近前肢处腹部皮下注射YCD K5 6 2B及K5 6 2B细胞 ,成瘤后治疗组腹腔注射 5 0 0mg kg 5 FC共 10d ,对照组腹腔注射生理盐水 ,观察瘤体相对体积变化及病理变化。结果　瘤细胞接种第 2 1天 ,瘤体相对体积分别为 :YCD K5 6 2B +5 FC组 2 .92 2± 0 .5 81,YCD K5 6 2B +生理盐水组 2 4.434± 4.790 ,K5 6 2B +5 FC组 2 2 .70 1± 2 35 0 ,K5 6 2B +生理盐水组 2 4.46 0± 1.6 70 ;YCD K5 6 2B +5 FC组与YCD K5 6 2B +生理盐水组相比差异非常显著 (P =0 0 0 0 1) ,K5 6 2B +5 FC组及K5 6 2B +生理盐水组相比 ,差异无显著性 (P =0 .0 96 ) ,表明 5 FC对转YCD基因的K5 6 2B白血病细胞有明显的杀伤效应 ,而对未转基因细胞的生长无影响 ;YCD K5 6 2B +5 FC组瘤体于瘤细胞接种后第 12～第 15天 (5 FC治疗的第 3～第 6天 )有所缩小 (最小的相对体积为 0 .6 81) ,病理检查可见 5 FC治疗组瘤体有以小动脉血管为中心的坏死。结论　YCD 5 FC系统在体内对转YCD     

Regulated overexpression of CDR1 in Candida albicans confers multidrug resistance

OBJECTIVES: Information on the function of Candida albicans ATP-binding cassette (ABC) membrane transporter Cdr1p has come from studying the effect of gene inactivation in C. albicans and from heterologous Cdr1p expression in the yeast Saccharomyces cerevisiae. These approaches, however, give only an indirect indication of Cdr1p function in C. albicans itself. The objective of this study was to determine Cdr1p function in C. albicans by induced overexpression of Cdr1p in a C. albicans CDR1-deleted strain. METHODS: The C. albicans CDR1 open reading frame was fused to the C. albicans HEX1 promoter and used to complement a CDR1-null mutant to create strain FL3. The effect of inducing the FL3 HEX1 promoter, by growth on medium containing N-acetylglucosamine (GlcNAc) as the carbon source, on CDR1 expression and drug susceptibility was determined. RESULTS: C. albicans FL3 cells grown on medium containing GlcNAc overexpressed CDR1 mRNA and a 170 kDa plasma membrane protein that reacted with anti-Cdr1p antibodies. Overexpression of Cdr1p in C. albicans FL3 conferred resistance to structurally unrelated chemicals such as terbinafine, brefeldin A, cerulenin and nigericin as well as to azole antifungal agents, but not resistance to polyene antibiotics. FK506, ascomycin and ciclosporin A chemosensitized FL3 to fluconazole. FL3 cells grown on GlcNAc effluxed 5.3 times as much Cdr1p substrate rhodamine 6G, over a 10 min period, as FL3 cells grown on glucose, and this rhodamine 6G efflux was inhibited by including fluconazole in the assay. CONCLUSION: This study provides the first direct demonstration of Cdr1p pump activity in C. albicans.     

Surface-active fungicidal D-peptide inhibitors of the plasma membrane proton pump that block azole resistance

A 1.8-million-member D-octapeptide combinatorial library was constructed in which each member comprised a diversity-containing N-terminal pentapeptide and a C-terminal amidated triarginine motif. The C-terminal motif concentrated the library members at the fungal cell surface. A primary screen for inhibitors of Saccharomyces cerevisiae and Candida albicans growth, together with an in vitro secondary screen with the S. cerevisiae plasma membrane ATPase (Pma1p) as a target, identified the antifungal D-octapeptide BM0 (D-NH(2)-RFWWFRRR-CONH(2)). Optimization of BM0 led to the construction of BM2 (D-NH(2)-RRRFWWFRRR-CONH(2)), which had broad-spectrum fungicidal activity against S. cerevisiae, Candida species, and Cryptococcus neoformans; bound strongly to the surfaces of fungal cells; inhibited the physiological activity of Pma1p; and appeared to target Pma1p, with 50% inhibitory concentrations in the range of 0.5 to 2.5 microM. At sub-MICs (<5 microM), BM2 chemosensitized to fluconazole (FLC) S. cerevisiae strains functionally hyperexpressing fungal lanosterol 14alpha-demethylase and resistance-conferring transporters of azole drugs. BM2 chemosensitized to FLC some FLC-resistant clinical isolates of C. albicans and C. dubliniensis and chemosensitized to itraconazole clinical isolates of C. krusei that are intrinsically resistant to FLC. The growth-inhibitory concentrations of BM2 did not cause fungal cell permeabilization, significant hemolysis of red blood cells, or the death of cultured HEp-2 epithelial cells. BM2 represents a novel class of broad-spectrum, surface-active, Pma1p-targeting fungicides which increases the potencies of azole drugs and circumvents azole resistance.     

Mechanisms of resistance to azole antifungal agents in Candida albicans isolates from AIDS patients involve specific multidrug transporters.

Azole antifungal agents, and especially fluconazole, have been used widely to treat oropharyngeal candidiasis in patients with AIDS. An increasing number of cases of clinical resistance against fluconazole, often correlating with in vitro resistance, have been reported. To investigate the mechanisms of resistance toward azole antifungal agents at the molecular level in clinical C. albicans isolates, we focused on resistance mechanisms related to the cellular target of azoles, i.e., cytochrome P450(14DM) (14DM) and those regulating the transport or accumulation of fluconazole. The analysis of sequential isogenic C. albicans isolates with increasing levels of resistance to fluconazole from five AIDS patients showed that overexpression of the gene encoding 14DM either by gene amplification or by gene deregulation was not the major cause of resistance among these clinical isolates. We found, however, that fluconazole-resistant C. albicans isolates failed to accumulate 3H-labelled fluconazole. This phenomenon was reversed in resistant cells by inhibiting the cellular energy supply with azide, suggesting that resistance could be mediated by energy-requiring efflux pumps such as those described as ATP-binding cassette (ABC) multidrug transporters. In fact, some but not all fluconazole-resistant clinical C. albicans isolates exhibited up to a 10-fold relative increase in mRNA levels for a recently cloned ABC transporter gene called CDR1. In an azole-resistant C. albicans isolate not overexpressing CDR1, the gene for another efflux pump named BENr was massively overexpressed. This gene was cloned from C. albicans for conferring benomyl resistance in Saccharomyces cerevisiae. Therefore, at least the overexpression or the deregulation of these two genes potentially mediates resistance to azoles in C. albicans clinical isolates from AIDS patients with oropharyngeal candidiasis. Involvement of ABC transporters in azole resistance was further evidenced with S. cerevisiae mutants lacking specific multidrug transporters which were rendered hypersusceptible to azole derivatives including fluconazole, itraconazole, and ketoconazole.