Multiple amino acid substitutions in lanosterol 14alpha-demethylase contribute to azole resistance in Candida albicans.
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Lanosterol 14alpha-demethylase (14DM) is the target of the azole antifungals, and alteration of the 14DM sequence leading to a decreased affinity of the enzyme for azoles is one of several potential mechanisms for resistance to these drugs in Candida albicans. In order to identify such alterations the authors investigated a collection of 19 C. albicans clinical isolates demonstrating either frank resistance (MICs > or = 32 microg ml(-1)) or dose-dependent resistance (MICs 8-16 microg ml(-1)) to fluconazole. In cell-free extracts from four isolates, including the Darlington strain ATCC 64124, sensitivity of sterol biosynthesis to inhibition by fluconazole was greatly reduced, suggesting that alterations in the activity or affinity of the 14DM could contribute to resistance. Cloning and sequencing of the 14DM gene from these isolates revealed 12 different alterations (two to four per isolate) leading to changes in the deduced amino acid sequence. Five of these mutations have not previously been reported. To demonstrate that these alterations could affect fungal susceptibility to azoles, the 14DM genes from one sensitive and three resistant C. albicans strains were tagged at the carboxyl terminus with a c-myc epitope and expressed in Saccharomyces cerevisiae under control of the endogenous promoter. Transformants receiving 14DM genes from resistant strains had fluconazole MICs up to 32-fold higher than those of transformants receiving 14DM from a sensitive strain, although Western blot analysis indicated that the level of expressed 14DM was similar in all transformants. Amino acid substitutions in the 14DM gene from the Darlington strain also conferred a strong cross-resistance to ketoconazole. In conclusion, multiple genetic alterations in C. albicans 14DM, including several not previously reported, can affect the affinity of the enzyme for azoles and contribute to resistance of clinical isolates. (+info)
Synergistic fungistatic effects of lactoferrin in combination with antifungal drugs against clinical Candida isolates.
(42/1523)
Because of the rising incidence of failures in the treatment of oropharyngeal candidosis in the case of severely immunosuppressed patients (mostly human immunodeficiency virus [HIV]-infected patients), there is need for the development of new, more effective agents and/or compounds that support the activity of the common antifungal agents. Since lactoferrin is one of the nonspecific host defense factors present in saliva that exhibit antifungal activity, we studied the antifungal effects of human, bovine, and iron-depleted lactoferrin in combination with fluconazole, amphotericin B, and 5-fluorocytosine in vitro against clinical isolates of Candida species. Distinct antifungal activities of lactoferrin were observed against clinical isolates of Candida. The MICs generally were determined to be in the range of 0.5 to 100 mg. ml(-1). Interestingly, in the combination experiments we observed pronounced cooperative activity against the growth of Candida by using lactoferrin and the three antifungals tested. Only in a limited concentration range was minor antagonism detected. The use of lactoferrin and fluconazole appeared to be the most successful combination. Significant reductions in the minimal effective concentrations of fluconazole were found when it was combined with a relatively low lactoferrin concentration (1 mg/ml). Such combinations still resulted in complete growth inhibition, while synergy of up to 50% against several Candida species was observed. It is concluded that the combined use of lactoferrin and antifungals against severe infections with Candida is an attractive therapeutic option. Since fluconazole-resistant Candida species have frequently been reported, especially in HIV-infected patients, the addition of lactoferrin to the existing fluconazole therapy could postpone the occurrence of species resistance against fluconazole. Clinical studies to further elucidate the potential utility of this combination therapy have been initiated. (+info)
Genetic analysis of azole resistance by transposon mutagenesis in Saccharomyces cerevisiae.
(43/1523)
The increasing resistance of Candida species to fluconazole is cause for concern. To determine the molecular mechanisms involved in resistance to fluconazole, I used a scheme of transposon mutagenesis in Saccharomyces cerevisiae, a genetically tractable yeast that is closely related to Candida albicans. This technique, which permits the generation and analysis of multiple random Tn3::LEU2::lacZ fusions, can be used as a disruption mutagen (N. B. Burns et al., Genes Dev. 8:1087-1105, 1994). By using the Tn3::LEU2::lacZ library as a disruption mutagen, I found recessive mutations in genes that were previously found to be involved in azole resistance, e.g., PDR5 and CPR1, and in genes previously found to be involved in azole sensitivity, e.g., ERG3. This approach also enabled me to identify recessive mutations in three genes not previously known to be involved in azole sensitivity. Two of the genes, ADA3 and SPT7, are general transcriptional regulators; the third, YMR034c, is a putative sterol transporter. Finally, by screening the Tn3::LEU2::lacZ library for lacZ fusions induced by a low concentration of fluconazole, I identified genes known to be induced by azoles as well as a variety of other genes not previously known to be induced by the drug. In conclusion, transposon mutagenesis is a promising screening tool for use in identifying novel drug targets and in uncovering the mechanisms involved in the response of S. cerevisiae to antifungal drugs. (+info)
Overexpression of Erg11p by the regulatable GAL1 promoter confers fluconazole resistance in Saccharomyces cerevisiae.
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The contribution of the dosage of target enzyme P-450 14alpha-demethylase (14alphaDM) to fluconazole resistance in both Candida albicans and Saccharomyces cerevisiae remains unclear. Here, we show that overexpression of Saccharomyces P-450 14alphaDM in S. cerevisiae, under the control of the regulatable promoter GAL1, results in azole resistance. (+info)
Further characterization of human salivary anticandidal activities in a human immunodeficiency virus-positive cohort by use of microassays.
(45/1523)
Salivary anticandidal activities play an important role in oral candidal infection. R. P. Santarpia et al. (Oral Microbiol. Immunol. 7:38-43, 1992) developed in vitro anticandidal assays to measure the ability of saliva to inhibit the viability of Candida albicans blastoconidia and the formation of germ tubes by C. albicans. In this report, we describe modifications of these assays for use with small volumes of saliva (50 to 100 microl). For healthy subjects, there is strong inhibition of blastoconidial viability in stimulated parotid (75%), submandibular-sublingual (74%), and whole (97%) saliva, as well as strong inhibition of germ tube formation (>80%) for all three saliva types. The susceptibility of several Candida isolates to inhibition of viability by saliva collected from healthy subjects is independent of body source of Candida isolation (blood, oral cavity, or vagina) or the susceptibility of the isolate to the antifungal drug fluconazole. Salivary anticandidal activities in human immunodeficiency virus (HIV)-infected patients were significantly lower than those in healthy controls for inhibition of blastoconidial viability (P < 0.05) and germ tube formation (P < 0. 001). Stimulated whole-saliva flow rates were also significantly lower (P < 0.05) for HIV-infected patients. These results show that saliva of healthy individuals has anticandidal activity and that this activity is reduced in the saliva of HIV-infected patients. These findings may help explain the greater incidence of oral candidal infections for individuals with AIDS. (+info)
Successful treatment of fluconazole-resistant oropharyngeal candidiasis by a combination of fluconazole and terbinafine.
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Increasing incidence of resistance to conventional antifungal therapy has demanded that novel therapies be introduced. Recent in vitro studies have shown that combinations involving azoles and allylamines may be effective in inhibiting fluconazole-resistant fungi. In this report, we describe the case of a 39-year-old woman who presented with white patches on her buccal mucosa, tongue, and palate with a bright erythematous erosive base. A fungal culture revealed Candida albicans. The patient failed to respond to the initially prescribed fluconazole therapy. Failure of therapy can be attributed to a developed resistance to fluconazole from the patient's intermittent use of this antifungal agent at varying dosages for the preceding 2 years due to a diagnosis of onychomycosis. In vitro testing of the culture from the patient showed elevated MICs of fluconazole, itraconzole, and terbinafine (MICs were 32, 0.5, and 64 microg/ml, respectively). Our goal was to combine therapies of fluconazole and terbinafine in an attempt to clear the fungal infection. Impressively, this combination resulted in the clearing of the clinical symptoms and the patient has successfully been asymptomatic for more than 12 months posttreatment. (+info)
Fluconazole versus itraconazole for the prevention of fungal infections in haemato-oncology.
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AIMS: To compare the efficacy of and tolerance to oral fluconazole and intraconazole in preventing fungal infection in neutropenic patients with haematological malignancies. PATIENTS: 213 consecutive, afebrile adult patients treated with or without autologous stem cell transplantation for haematological malignancies. METHODS: A randomised, double blind, single centre study. Patients were randomly assigned to receive fluconazole 50 mg or itraconazole 100 mg, both twice daily in identical capsules. An intention to treat analysis was performed on 202 patients, 101 in each group. RESULTS: Microbiologically documented systemic fungal infections occurred in four patients in each group. Clinical fungal infection was thought to be present in seven recipients of fluconazole and four of itraconazole. In all 202 patients, 29 proceeded to intravenous amphotericin (amphotericin B), 16 in the fluconazole group and 13 in the itraconazole group. Superficial fungal infection was seen only in three non-compliant patients in the fluconazole group. All these infections were oral. No major differences were noted in the isolates of fungi in mouth washes and fecal samples. Overall mortality was 8.9% (18 deaths; seven in the fluconazole group, 11 in the itraconazole group). Mortality from microbiologically and clinically documented fungal infection was 4.5% (nine deaths; three in the fluconazole group, six in the itraconazole group). Median time to suspected or proven fungal infection was 16 days in both groups. None of these comparisons reached statistical significance (p < 0.05). No major clinical toxicity was noted and compliance was excellent. CONCLUSIONS: In neutropenic patients treated for haematological malignancies with or without autologous stem cell transplantation, fluconazole and itraconazole in low doses result in a similar low frequency of fungal disease. Fluconazole may be the preferable drug because of the smaller number of capsules and lack of need for timing relative to meals. (+info)
Detection of fluconazole-resistant Candida strains by a disc diffusion screening test.
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A commercial disc diffusion test has been evaluated as a screening method for the detection of Candida species with decreased susceptibility to fluconazole. A total of 1,407 Candida strains of different species were tested, and the results were compared with the MIC results. The recently published National Committee for Clinical Laboratory Standards breakpoint criteria have been used. Isolates were classified as susceptible if the MIC for the isolates was /=64 microg/ml. All 77 resistant strains and 121 of 122 S-DD strains had fluconazole zone diameters of +info)