Resistance of Candida species to fluconazole

Pharmacokinetics of fluconazole in saliva and plasma after administration of an oral suspension and capsules

The concentrations of fluconazole were determined at steady state in the saliva and plasma of 10 healthy volunteers after ingestion of fluconazole as capsules and after flushing the mouth for 2 min with the same dose formulated as an oral suspension and swallowing of the drug. Saliva and plasma samples were analyzed by a validated high-performance liquid chromatographic assay. Flushing and swallowing of the oral suspension resulted in a significantly (P = 0.005) higher mean area under the concentration-versus-time curve (AUC) from 0 to 24 h in saliva (89.13 +/- 23.42 mg.h/liter) than that obtained after ingestion of the same dose as capsules (69.27 +/- 12.89 mg . h/liter). The calculated mean maximum concentration in saliva just after swallowing of the suspension was 97.99 +/- 6.12 mg/liter. The peak fluconazole concentration in saliva after the ingestion of the capsules was 3.55 +/- 0.40 mg/liter. The fluconazole oral suspension and capsules resulted in comparable concentrations and AUCs in plasma. Thus, because of a higher local level of drug exposure in terms of both higher peak concentrations in saliva and a higher salivary AUC, the fluconazole oral suspension has theoretical advantages over the capsule formulation in the treatment of oropharyngeal candidiases.

Antibiotic resistant Streptococcus pneumoniae

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Response to fluconazole by 23 patients with human immunodeficiency virus infection and oral candidiasis: pharmacological and mycological factors

The MICs of fluconazole for strains of Candida species and the levels of fluconazole in serum were determined at day 0 and day 14 for 23 human immunodeficiency virus-infected patients with oral candidiasis who were treated orally with 100 mg of fluconazole per day for 14 days. Among the 23 patients, 11 (48%) were not clinically cured and had persistent isolation of Candidiasis albicans (n = 10) and/or presence of non-C. albicans (n = 6). Clinical response could be predicted by the susceptibility of the strain to fluconazole determined at day 0. All 12 patients who were cured were infected with a strain for which the MIC was < 0.78 mg/liter. All four patients who were infected with a strain for which the MIC was > 3.12 mg/liter experienced clinical failure. These data suggest that a C. albicans strain could be defined as being susceptible when the MIC of fluconazole is < 0.78 mg/liter and as being resistant when the MIC is > 3.12 mg/liter.

Characterization of echinocandin-resistant mutants of Candida albicans: genetic, biochemical, and virulence studies

The pneumocandins are potent antifungal agents of the echinocandin class which are under development for use as broad-spectrum antimycotic therapy. One important consideration for any new therapeutic class for treating serious fungal infections is the potential for drug resistance development. In this study we have isolated and characterized four independent spontaneous Candida albicans mutants resistant to the potent semisynthetic pneumocandin L-733,560. These mutants have many of the properties of FKS1/ETG1 echinocandin-resistant mutants of Saccharomyces cerevisiae, including (i) cross-resistance to other 1,3-beta-D-glucan synthase inhibitors, such as papulacandin and echinocandins, but no change in sensitivity to other antifungal agents; (ii) in vitro glucan synthase activity that is more resistant to pneumocandins than the wild-type parent enzyme; and (iii) semidominant drug resistance in spheroplast fusion strains. The mutants were compared with C. albicans echinocandin-resistant mutants isolated by mutagenesis by L. Beckford and D. Kerridge (mutant M-2) (abstr. PS3.11, in Proceedings of the XI Congress of the International Society for Human and Animal Mycology, Montreal, Canada, 1992) and by A. Cassone, R. E. Mason, and D. Kerridge (mutant CA-2) (Sabouraudia 19:97-110, 1981). All of the strains had resistant enzyme activity in vitro. M-2 grew poorly and had low levels of enzyme activity. In contrast, CA-2 and the spontaneous mutants grew as well as the parents and had normal levels of glucan synthase activity. These results suggest that these resistant mutants may have alterations in glucan synthase. CA-2 was unable to form germ tubes, an ability retained by the spontaneous mutants. The virulence of the spontaneous mutants was unimpaired in a mouse model of disseminated candidiasis, while M-2 and CA-2 were 2 orders of magnitude less virulent than their parent strains. Significantly, mice challenged with the spontaneous mutant CAI4R1 responded therapeutically to lower levels of L-733,560 than would he predicted by the increase in in vitro susceptibility.

Simple method for detecting fluconazole-resistant yeasts with chromogenic agar

A method for detecting fluconazole-resistant yeasts was developed that uses chromogenic agar containing fluconazole. Yeasts were plated on media with fluconazole at 0, 8, and 16 micrograms/ml. On media without fluconazole, normal growth of susceptible yeasts (defined as those having a fluconazole MIC of < 8 micrograms/ml) was detected, while fluconazole-containing media suppressed susceptible strains and normal colonies of resistant yeasts (fluconazole MICs of > or = 8 micrograms/ml) were detected. This method was used to screen for resistance in oropharyngeal candidiasis. Isolates having fluconazole MICs of > or = 8 micrograms/ml and < 8 micrograms/ml were correctly predicted in 43 of 45 cultures and 115 of 116 cultures, respectively. This screening method appears to be rapid and sensitive for detection of fluconazole-resistant yeasts.

Emerging fungal infections in cancer patients

The increasing number of reports in cancer patients that describe unusual or new fungal pathogens in severe systemic infections may be due, in part, to new treatment regimens but also to increased recognition of clinical disease by physicians and unusual organisms by microbiologists. Identification of these pathogens requires specialized expertise but the diagnosis may often be too late to permit effective therapeutic intervention. An unfortunate limitation of current antifungal agents is their limited efficacy in the heavily immunosuppressed, even when the drugs show good activity in vitro. Infections with Candida spp., and non-Candida yeasts and moulds are often disseminated and are frequently fatal in patients with severe immunosuppression. Therapeutic outcomes could be improved with more precise and rapid diagnostic procedures, standardized treatments for each pathogen and improved therapeutic agents. Liposomal amphotericin B formulations, new azole antifungals, more aggressive surgery and haemopoietic growth factors may improve the poor outcome that currently occurs with many of those infections.

Genetic dissimilarity of two fluconazole-resistant Candida albicans strains causing meningitis and oral candidiasis in the same AIDS patient

We describe a patient with AIDS who simultaneously developed Candida meningitis with three positive cerebrospinal fluid cultures and oral candidiasis. This patient also had a history or recurrent episodes of oral candidiasis treated with fluconazole. The patient did not respond to this therapy but was cured with amphotericin B and flucytosine. In vitro susceptibility tests revealed that each infection was caused by fluconazole-resistant Candida albicans isolates. Strain delineation by karyotyping, NotI restriction pattern analysis, hybridization with the specific probe 27A, and PCR fingerprinting with the phage M13 core sequence clearly demonstrated that meningitis and oral thrush were caused by two genetically different isolates.

Comparison of D0870, a new triazole antifungal agent, to fluconazole for inhibition of Candida albicans cytochrome P-450 by using in vitro assays

D0870 was 12 to 15 times more active than fluconazole in experiments to determine the MIC for growth arrest for two isolates of Candida albicans. A biochemical comparison of in vitro sterol biosynthesis in cell extracts showed only a twofold superiority of D0870 over fluconazole. A large differentiation (10-fold) in 50% saturating concentrations obtained by examining the binding of the azoles to microsomal P-450 was observed in a type II binding spectrophotometric assay, possibly reflecting the differential affinity for more than one P-450 enzyme. Additional mechanisms besides affinity for the target enzyme sterol 14 alpha-demethylase, such as differential intracellular accumulation of drug, may contribute to the differences in antifungal activity.

Asymptomatic oral yeast carriage in HIV-infected patients: frequency and fluconazole susceptibility profile

OBJECTIVES: Fluconazole-resistant oropharyngeal candidiasis (OPC) is a rapidly growing problem in HIV-infected patients. To better understand the pathogenesis of fluconazole resistance in this setting, asymptomatic candidal carriage was determined by means of oral swabs regularly performed in all patients without clinical signs of OPC seen at our HIV outpatient clinic. Controls were 204 asymptomatic healthcare workers without previous exposure to fluconazole. METHODS: Swabs were plated on three solid media and put in a Sabouraud broth. Phenotypically different colonies were identified to the species level. Susceptibility to fluconazole was determined using a disk diffusion test with 50 microg fluconazole disks on yeast nitrogen agar, with a cut-off value of 25 mm. RESULTS: Swabs were performed in 538 consecutive HIV-positive patients, of whom 216 (40%) had had prior episode(s) of OPC and/or were previously exposed to fluconazole. Yeasts were grown in 418/538 HIV-positive patients (78%), compared to 57/204 controls (28%) (p < 0.05). In HIV-positive patients, yeasts were grown in 189/216 (88%) of those with past fluconazole exposure, and in 229/322 (71%) without exposure (p < 0.05). A total of 589 isolates were grown in the 538 HIV-positive patients (451 C. albicans, 88 C. glabrata, 22 C. tropicalis, 11 C. krusei, and 17 isolates from 12 other species). Resistance to fluconazole was present in 121/589 (21%) Candida species isolates in HIV-positive patients and in 2/59 (3%) in controls. Among C. albicans isolates, there were 18 fluconazole-resistant strains in HIV-positive patients (4%) and none in controls.CONCLUSIONS: Using sensitive culture methods, oral yeast colonization was detected significantly more frequently in HIV-infected patients (78%) than in a control group of HIV-negative persons (28%). In addition, yeast colonization was quantitatively more important in patients with lower CD4+ lymphocyte counts and for those who had been exposed to fluconazole for episode(s) of OPC. Fluconazole-resistant C. albicans isolates were observed only in HIV-positive patients, and all patients (17/18) for whom this information could be ascertained had had prior exposure to fluconazole.

Variation in fluconazole efficacy for Candida albicans strains sequentially isolated from oral cavities of patients with AIDS in an experimental murine candidiasis model

Four strains of Candida albicans, isolated from two patients with AIDS who had undergone prolonged fluconazole therapy for oral candidiasis, were studied in a model of disseminated murine candidiasis. Pre- and posttreatment isolates from each patient were genetically related, and the fluconazole MICs for the strains had increased significantly, from 0.25 to 32 micrograms/ml for the strains isolated from patient 1 and from 1.0 to 16 micrograms/ml for the strains isolated from patient 2. Mice were infected intravenously and were treated orally with fluconazole. For survival studies, mice were treated from day 1 to day 10 postinfection and were observed through day 30. The fluconazole dosages were as follows: 0.25, 0.5, 1.0, and 5.0 mg/kg of body weight twice a day. For tissue burden studies, two groups of mice (each group received fluconazole at 0.25 or 5.0 mg/kg) were treated from day 1 to day 7 and were sacrificed 1 day later for quantitative tissue cultures of the spleen and both kidneys. For pretreatment isolates from both patients, all fluconazole dosing regimens were effective at prolonging survival compared with the survival of the control groups. For posttreatment isolates, only fluconazole at 5.0 mg/kg was effective at prolonging survival. Both fluconazole dosing regimens used in the tissue burden studies significantly reduced the counts of the pretreatment isolate from patient 1 in the spleen and kidney, while fluconazole at 5.0 mg/kg was effective at reducing the counts of the posttreatment isolate. For both isolates from patient 2, only fluconazole at 5.0 mg/kg was effective at reducing the counts in the spleen and kidney. The study indicates that C. albicans mutation to resistance to fluconazole may play a critical role in fluconazole-refractory oral candidiasis in AIDS patients.

Typing Candida albicans oral isolates from human immunodeficiency virus-infected patients by multilocus enzyme electrophoresis and DNA fingerprinting

A total of 189 Candida albicans isolates have been typed by multilocus enzyme electrophoresis. The results obtained confirm the clonal mode of reproduction of C. albicans. The C. albicans populations found in the oropharynx of human immunodeficiency virus (HIV)-infected patients, in the oropharynx of healthy carriers, or in association with invasive candidiasis could not be distinguished. No clone or group of clones could be associated with the appearance of clinical disorders or with a reduced in vitro susceptibility to the antifungal agent fluconazole. Multiple and sequential oral isolates from 24 HIV-infected patients were also typed by restriction enzyme analysis with the enzymes EcoRI and HinfI and by use of the Ca3 repetitive probe. The results obtained by the combination of all three typing methods show that all but one patient each carried a unique major C. albicans clone in their oropharynx. The 21 patients with sequential isolates had the same C. albicans clones in their throats during recurrent oropharyngeal candidiasis episodes, independently of clinical status or of changes of in vitro susceptibility to fluconazole. Finally, several isolates of the same C. albicans clone found simultaneously in the oropharynx of a patient may present different levels of susceptibility to fluconazole.

In vitro activities of semisynthetic pneumocandin L-733,560 against fluconazole-resistant and -susceptible Candida albicans isolates

Lipopeptide L-733,560 is a water-soluble derivative of pneumocandin B0 that exhibits enhanced anti-Candida activity. We investigated the in vitro activity of L-733,560 compared with those of amphotericin B, flucytosine, and itraconazole, against fluconazole-resistant (n = 44) and fluconazole-susceptible (n = 46) Candida albicans isolates. Tests were performed with a photometer-read broth microdilution method with RPMI-2% glucose and National Committee for Clinical Laboratory Standards reference strains. Except for those of itraconazole, MICs were not significantly different between the two groups of isolates, as expected for agents with different mechanisms of action. L-733,560 was the most active agent against C.albicans, with MICs for 50 and 90% of the strains tested of 0.01 and 0.06 microgram/ml, respectively.

Susceptibility testing of fungi: current status of correlation of in vitro data with clinical outcome

In summary, it is clear that in vitro susceptibility testing can predict outcome in selected clinical situations. The clearest data are from the fluconazole-treated AIDS patients with oropharyngeal candidiasis. In this setting, the homogeneity of the underlying immune defect, combined with the ease of identification and monitoring of the infection, creates a near-perfect test situation. In more complex scenarios, such as the heterogeneous population of patients enrolled in a recent study of candidemia, no such clear-cut correlation was present. The importance of host factors in the correlation of the MIC with outcome cannot be overemphasized. Examples of these parameters include patient status (underlying disease, the presence of intravascular catheters, and CD4+ T-cell number), drug pharmacokinetics (absorption and distribution), patient compliance, and drug-drug interactions. Identification of relevant factors can substantially improve the degree of the MIC-outcome correlation and thus improve the clinical utility of in vitro testing. An important feature in this entire process is the role of standardized susceptibility testing procedures. While not without flaws, the proposed NCCLS reference method has been invaluable in allowing multiple investigators to contribute data that can be used to clarify the correlation between the fluconazole MIC and outcome. While the development of simplified second-generation methods is eagerly anticipated, the role of the reference method as a common touchstone is critical. Only by use of either the reference method itself or methods with a known relationship to the reference method can this broad collaborative process really proceed. Current work is focusing on defining interpretive breakpoints for fluconazole and Candida species, refinement of the in vitro procedures used to measure susceptibility to amphotericin B, ketoconazole, and itraconazole, and the acquisition of a broad base of data on the relationship between the MIC and outcome for these three drugs. Although considerable work remains to be done, the available data suggest that solutions to each of these problems are possible and that routine susceptibility testing of fungi will become meaningful for clinical decision making in the foreseeable future.

In vitro susceptibilities of clinical and environmental isolates of Cryptococcus neoformans to five antifungal drugs

A total of 53 Cryptococcus neoformans strains, including clinical and environmental Brazilian isolates, were tested for their susceptibilities to amphotericin B, 5-flucytosine, ketoconazole, fluconazole, and itraconazole. The tests were performed according to the National Committee of Clinical Laboratory Standards recommendations (document M27-P). In general, there was a remarkable homogeneity of results for all strains, and comparable MICs were found for environmental and clinical isolates. This paper represents the first contribution in which susceptibility data for Brazilian C. neoformans isolates are provided.

Susceptibilities of Candida spp. to antifungal agents visualized by two-dimensional scatterplots of relative growth

The growth of 811 clinical yeast isolates in the presence of single concentrations of antifungal agents was measured spectrophotometrically and expressed as a percentage of growth in inhibitor-free control cultures. Two-dimensional scatterplots of the relative growth data allowed for the simple visual determination of some susceptibility trends, including correlations in relative growth between different agents and in relative susceptibilities between different yeast species. A positive susceptibility correlation was found for relative growth results with the azole antifungal agents fluconazole, itraconazole, and ketoconazole for 504 Candida albicans isolates. The relative growth scatterplots for fluconazole versus itraconazole showed that 50 (9.9%) of 504 C. albicans isolates were outliers with respect to the 95% confidence limits for a line of correlated relative growth established with an initial test panel of 59 isolates of this species. The outlying isolates were relatively less susceptible to fluconazole than to itraconazole under the conditions of the test. Most of the outliers were received in 1993 and 1994; only 3.9% of the isolates received in 1991 and 1992 and 1.7% of the isolates received before 1991 showed this differential susceptibility. In addition, most of the outliers came from patients with human immunodeficiency virus infections. The relative growth scatterplots confirmed the known high susceptibility of most Candida parapsilosis isolates to both fluconazole and itraconazole and the specifically low susceptibility of Candida krusei isolates to fluconazole. The scatterplots also illustrated a tendency towards lower (and correlative) relative growth among oral isolates obtained from AIDS patients who responded to azole antifungal treatment than among isolates from clinical nonresponders.

Correlation between rhodamine 123 accumulation and azole sensitivity in Candida species: possible role for drug efflux in drug resistance

A wide variety of prokaryotic and eukaryotic cells exhibit a multidrug resistance (MDR) phenotype, indicating that resistance to potentially toxic compounds is mediated by their active efflux from the cell. We have sought to determine whether resistance to azoles in some strains of Candida species may be due in part to active drug efflux. Rhodamine 123 (Rh123) is a fluorescent compound that is transported by a wide variety of MDR cell types. We have shown that certain azole-resistant strains of Candida albicans, C. glabrata, and C. krusei accumulate less Rh123 than azole-susceptible ones. In C. albicans, Rh123 accumulation was growth phase and temperature dependent and was increased by proton uncouplers and by reserpine, an MDR modulator. This is consistent with an energy-dependent efflux mechanism for Rh123, mediated by an MDR transporter. In C. glabrata, but not in C. albicans, there was competition between Rh123 and fluconazole for efflux. Thus, in C. glabrata, Rh123 and fluconazole appear to be transported via a common MDR-like transporter, whereas in C. albicans, the Rh123 transporter does not appear to transport azoles.

Evaluation of a commercial medium for identification of Candida species

CHROMagar Candida (CHROMagar, France) was evaluated as a medium for the presumptive identification and isolation of yeasts using 1,537 isolates of medically important yeasts, including 970 Candida albicans, 165 Candida parapsilosis, 131 Candida glabrata, 62 Candida guilliermondii, 35 Candida krusei, 32 Candida tropicalis, 31 Rhodotorula rubra, 23 Trichosporon spp. (17 Trichosporon beigelii), 17 Candida famata, 16 Candida pelliculosa, 10 Pichia etchelsii, 10 Saccharomyces cerevisiae, 8 Candida lusitaniae, 7 Cryptococcus spp., and 20 isolates of other Candida spp. After 48 h of incubation at 37 degrees C, the sensitivity and specificity were, respectively, 99% and 100% for Candida albicans, 93.8% and 99.1% for Candida tropicalis, and 100% and 100% for Candida krusei. In addition to colony color, other colony characteristics were important for identification of some species, such as rough colonies in Candida krusei isolates or the halo around the colonies of Candida tropicalis. A great variety of colors was observed among species other than Candida albicans, Candida tropicalis, and Candida krusei. For identification purposes, CHROMagar Candida medium has an accuracy similar to that of germ-tube tests and chlamydospore development tests for Candida albicans and to that of the ATB ID32C kit (API, bioMérieux, France) for Candida tropicalis and Candida krusei.

[Susceptibility testing of fluconazole: evaluation of a multicenter study of the working group "Clinical Mycology" of the German Speaking Mycological Society]

In a collaborative study for in vitro testing of fluconazole against clinical yeast isolates participated 21 laboratories of the working group "Clinical Mycology" of the German Speaking Mycological Society. In these centers, according to a standard test protocol 1181 clinical isolates from 1033 patients were tested to their susceptibility against fluconazole by microdilution, agar diffusion and partly by agar dilution. Approximately 600 strains (59.1%) of the collective of 1106 isolates sent to a reference center underwent retesting in one laboratory (center 13). These strains demonstrated almost the same species distribution as the total collective. For 80% of all isolates a MIC of < or = 4 micrograms/ml and for 90% of the Candida albicans strains a MIC of < or = 2 micrograms/ml has been determined. Only approx, 9% of all isolates (4% with Candida albicans) showed a MIC of < or = 25 micrograms/ml. By parallel testing of 10 control strains issued by the reference center to the laboratories, the inter- and intra-laboratory comparability of the susceptibility testing of fluconazole was checked. The results demonstrated that under appropriate technical prerequisites and standardised test conditions, the methods used routinely in bacteriology microdilution, agar dilution and agar diffusion may also be applied in a reproducible way in the routine mycological laboratory for the susceptibility testing of yeasts.

Antifungal azoxybacilin exhibits activity by inhibiting gene expression of sulfite reductase

Azoxybacilin, produced by Bacillus cereus, has a broad spectrum of antifungal activity in methionine-free medium and has been suggested to inhibit sulfite fixation. We have further investigated the mode of action by which azoxybacilin kills fungi. The compound inhibited the incorporation of [35S] sulfate into acid-insoluble fractions of Saccharomyces cerevisiae under conditions in which virtually no inhibition was observed for DNA, RNA, or protein synthesis. It did not interfere with the activity of the enzymes for sulfate assimilation but clearly inhibited the induction of those enzymes when S. cerevisiae cells were transferred from rich medium to a synthetic methionine-free medium. Particularly strong inhibition was observed in the induction of sulfite reductase. Northern (RNA) analysis revealed that azoxybacilin decreased the level of mRNA of genes for sulfate assimilation, including MET10 for sulfite reductase and MET4, the transactivator of MET10 and other sulfate assimilation genes. When activities of azoxybacilin were compared for mRNA and enzyme syntheses from MET10, the concentration required for inhibition of transcription of the gene was about 10 times higher (50% inhibitory concentration = 30 micrograms/ml) than that required for inhibition of induction of enzyme synthesis (50% inhibitory concentration = 3 micrograms/ml). The data suggest that azoxybacilin acts on at least two steps in the expression of sulfite reductase; the transcriptional activation of MET4 and a posttranscriptional regulation in MET10 expression. We conclude that azoxybacilin exhibits antifungal activity by interfering with the regulation of expression of sulfite reductase activity.

[In vitro susceptibility testing of Candida species against fluconazole using the microdilution test with Alamar Blue]

The investigation of susceptibility of Candida species to fluconazole was performed in microdilution to a supplemented HR-medium. The sufficient reproducibility of the test was verified using special control isolates and isolates of patients. The excellent applicability of the method in routine diagnostics was evaluated by in vitro testing of susceptibility of 279 Candida isolates from patients being colonised or suffering from endomycoses. The Candida species showed different susceptibility against fluconazole: 96% of the C. albicans isolates were sensitive, 55% of the C. glabrata isolates had a reduced sensitivity, and 26% were resistant against fluconazole (MIC > 25 micrograms/ml). C. krusei isolates were highly resistant (9 of 11 strains).

Reasons for the emergence of antibiotic resistance

The ability of many different species of bacteria, including those that cause diseases in humans, to resist the inhibitory action of antimicrobial agents has become a global problem. Resistance continues to spread not only in nosocomial pathogens but in several key community-acquired organisms as well. Appropriate control measures for such resistant organisms depend in part on the pathways by which resistance has arisen. Unfortunately, these pathways differ greatly from organism to organism and setting to setting. In addition, although the epidemiology of resistant organisms sometimes is similar to that of susceptible organisms of the same kind, in some situations it may be quite different. In this article, the authors highlight some of the pathways leading to the development of resistance in bacteria, the importance of antimicrobial use, and the relevance of these mechanisms to measures for the control of resistant bacteria in hospital and community settings.

Fungal infections: a growing threat

THE EMERGENCE OF newly identified fungal pathogens and the reemergence of previously uncommon fungal diseases is primarily related to increases in the numbers of susceptible persons: people with HIV infection, bone marrow and organ transplant recipients, cancer patients being treated with chemotherapy, critically ill persons, and very low birth weight ( < or = 1500 g) infants. These immunocompromised populations are at risk for infection not only with opportunistic pathogens (for example, Pneumocystis, Candida, Cryptococcus, Trichosporon, Malassezia, Aspergillus, Penicillium marneffei, and numerous other moulds or yeasts) but also with fungal pathogens that usually infect otherwise healthy persons not previously exposed to endemic fungi (for example, Coccidioides immitis, Histoplasma capsulatum, and Blastomyces dermatitidis) and Sporothrix schenckii. Morbidity, mortality, and health care costs associated with fungal infections are high. Addressing the emergence of fungal diseases will require increased surveillance coupled with the availability of rapid, noninvasive diagnostic tests; monitoring the development of resistance to antifungal agents; and research focused on the understanding, prevention, and control of fungal infections.

Targeting fungi: a challenge

Invasive fungal infections are more commonly identified in various categories of patients, mainly in cancer patients but also in those undergoing organ transplantation, patients in intensive care units, and those with AIDS. There is a great need to increase the awareness of practitioners who are still underestimating the morbidity and mortality relating to invasive fungal infections, and to stress the economic burden for the society and healthcare systems of invasive fungal infections. The list of fungal pathogens causing life-threatening complications has also increased recently, with the emergence of unusual fungi being more frequently identified in such settings. Early diagnosis of invasive fungal infections is still a major challenge for the clinician at the bedside. Identification of state-of-the-art management is also a difficult task for the clinical scientist involved in the assessment of optimal strategies to prevent and to treat those invasive fungal infections, although major progress has occurred in the last 5 years with the development of new, safe, and effective antifungal agents. Empiric therapy remains a very controversial issue that should be further investigated in high-quality clinical trials. Overall, clinical research in this difficult field requires independent and objective analysis; only large multicenter clinical trials can address these critical issues and rapidly provide convincing results leading to a better prognosis of patients with invasive fungal infections. These complications still represent too often an obstacle to successful control of severe underlying diseases. Clinical research on the appropriate ways to target fungi will not only define state-of-the-art management but also identify ineffective or redundant treatments. Such an approach will make a substantial contribution to the care of the high-risk patients within the next decade and will preserve our capacity for medical excellence.

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.

Altered P450 activity associated with direct selection for fungal azole resistance

Azole antifungals inhibit CYP51A1-mediated sterol 14 alpha-demethylation and the mechanism(s) of resistance to such compounds in Ustilago maydis were examined. The inhibition of growth was correlated with the accumulation of the substrate, 24-methylene-24,25-dihydrolanosterol (eburicol), and depletion of ergosterol. Mutants overcoming the effect of azole antifungal treatment exhibited a unique phenotype with leaky CYP51A1 activity which was resistant to inhibition. The results demonstrate that alterations at the level of inhibitor binding to the target site can produce azole resistance. Similar changes may account for fungal azole resistance phenomena in agriculture, and also in medicine where resistance has become a problem in immunocompromised patients suffering from AIDS.

Fluconazole. An update of its pharmacodynamic and pharmacokinetic properties and therapeutic use in major superficial and systemic mycoses in immunocompromised patients

Fluconazole is a triazole antifungal agent which is now an established part of therapy in patients with immune deficiencies. It is effective against oropharyngeal/oesophageal candidiasis (candidosis) when used orally once daily either as treatment or secondary prophylaxis in patients with AIDS or as treatment or primary prophylaxis in neutropenia associated with cancer therapy. Fluconazole also resolves symptoms in up to 60% of patients with cryptococcal meningitis and AIDS. However, in this infection its efficacy as treatment relative to that of amphotericin B is equivocal, and its major role is as the drug of choice for maintenance therapy following amphotericin B induction. In this regard, fluconazole has been proven superior to amphotericin B and to itraconazole 200 mg/day. Comparisons with other drugs used for the treatment of mucosal candidiasis in patients with AIDS show fluconazole to be superior to nystatin, similar to itraconazole and at least as effective as clotrimazole and ketoconazole; it was more so than the latter azole in 1 study. In patients undergoing chemotherapy or bone marrow transplantation, fluconazole as primary prophylaxis has produced greater clinical benefit than a clotrimazole regimen. The incidence of adverse events appears to be somewhat higher in patients with AIDS compared with HIV-negative cohorts, but the qualitative pattern of events is similar. The most frequent events are gastrointestinal complaints, headache and skin rash: rare exfoliative skin reactions and isolated instances of clinically overt hepatic dysfunction have occurred in patients with AIDS. Issues yet to be clarified include: the use of fluconazole in children with AIDS, in whom results have been promising; its efficacy against other fungal infections encountered in immunocompromised patients; whether the drug influences mortality, as has been suggested by one placebo-controlled trial in patients undergoing bone marrow transplant; and the appropriateness of its potential for use as primary prophylaxis against cryptococcal meningitis in patients with AIDS, where it shows efficacy but there is concern over increasing risk of development of secondary resistance. Notwithstanding these undefined aspects of its clinical profile, fluconazole is now confirmed as an important antifungal drug in the management of fungal infections in patients with immune deficiencies. In patients with AIDS it is the present drug of choice as maintenance therapy against cryptococcal meningitis and is a preferred agent for secondary prophylaxis against candidal infections; it is also a favoured agent for primary prophylaxis in patients at risk because of neutropenia associated with chemotherapy or bone marrow transplantation .

Torulopsis glabrata: azole susceptibilities by microdilution colorimetric and macrodilution broth assays

Fluconazole and itraconazole MICs were determined by both the standard macrodilution method of the National Committee for Clinical Laboratory Standards and a colorimetric broth microdilution method for 140 isolates of Torulopsis (Candida) glabrata obtained over a 15-year period. Using the method of the National Committee for Clinical Laboratory Standards the MICs at which 90% of isolates are inhibited (MIC50) for all isolates were 32 and 1.6 micrograms/ml for fluconazole and itraconazole, respectively. For fluconazole, the MIC90 rose from 16 to > 64 micrograms/ml when the MIC90s for isolates collected from July 1980 to June 1991 were compared with those for isolates collected from July 1991 to March 1995. For itraconazole, the MIC90s for isolates from the same time periods were 0.8 and 3.2 micrograms/ml, respectively. Although for isolates from some non-human immunodeficiency virus-infected patients the MICs rose, most of the high MICs were found for isolates from human immunodeficiency virus-infected patients who had been extensively treated with azole drugs for thrush. The colorimetric method yielded endpoints that were more definitive; concordances within 2 dilutions for the two methods were 87% for fluconazole and 86% for itraconazole.

Comparative evaluation of macrodilution and alamar colorimetric microdilution broth methods for antifungal susceptibility testing of yeast isolates

A comparative evaluation of the macrodilution method and the Alamar colorimetric method for the susceptibility testing of amphotericin B, fluconazole, and flucytosine was conducted with 134 pathogenic yeasts. The clinical isolates included 28 Candida albicans, 17 Candida tropicalis, 15 Candida parapsilosis, 12 Candida krusei, 10 Candida lusitaniae, 9 Candida guilliermondii, 18 Torulopsis glabrata, and 25 Cryptococcus neoformans isolates. The macrodilution method was performed and interpreted according to the recommendations of the National Committee for Clinical Laboratory Standards (document M27-P), and the Alamar colorimetric method was performed according to the manufacturer's instructions. For the Alamar colorimetric method, MICs were determined at 24 and 48 h of incubation for Candida species and T. glabrata and at 48 and 72 h of incubation for C. neoformans. The overall agreement within +/- 1 dilution for Candida species and T. glabrata against the three antifungal agents was generally good, with the values for amphotericin B, fluconazole, and flucytosine being 85.3, 77.9, and 86.2%, respectively, at the 24-h readings and 69.3, 65.2, and 97.2%, respectively, at the 48-h readings. Most disagreement was noted with fluconazole against C. tropicalis and T. glabrata. Our studies indicate that determination of MICs at 24 h by the Alamar colorimetric method is a valid alternate method for testing amphotericin B, fluconazole, and flucytosine against Candida species but not for testing fluconazole against C. tropicalis and T. glabrata. For flucytosine, much better agreement can be demonstrated against Candida species and T. glabrata at the 48-h readings by the Alamar method. Excellent agreement within +/- dilution can also be observed for amphotericin B, fluconazole, and flucytosine (80, 96, and 96%, respectively) against c. neoformans when the MICs were determined at 72 h by the Alamar method.

Evaluation of new technology in the clinical microbiology laboratory

Technology capable of significantly influencing the practice of clinical microbiology is evolving at an ever-accelerating rate. During their early developmental years, it is difficult to predict which evolving technologies will prove amenable for use in hospital laboratory settings. With the considerable and increasing cost constraints placed on our medical institutions and the resulting budgetary pressures exerted on clinical laboratories, evaluation of developing technology is essential. The Clinical Laboratory Improvement Act of 1988 mandates correlation studies by clinical laboratories as part of the evaluation of all new assays to compare their sensitivities and specificities with those obtained using established methodologies. With shrinking numbers of technologists available for such evaluations, however, the mechanism with which this will be accomplished promises to pose a significant challenge. Factors that demand consideration in any such evaluation include (but are not restricted to) utility, accuracy, prospective time savings, cost of related instrumentation and reagents, and potential for diverse applications. Specific current examples that exemplify the need for such evaluations include the emergence of gene-based techniques such as the polymerase chain reaction as clinical tools, availability of new blood culture systems based on divergent sensor systems, and varying techniques for the the detection of antibodies and antigens for the serodiagnosis of infectious diseases. We as clinical microbiologists have the opportunity to approach the challenges confronting us regarding evaluation of developing technologies with responsible innovation and insight. Only by embracing these responsibilities can we hope to influence the impact of health care reform in the hospital laboratory setting.

Antifungal susceptibility testing of yeasts: evaluation of technical variables for test automation

The technical parameters for antifungal susceptibility testing with Candida species were reexamined to determine the optimal conditions for testing with semiautomated preparations of broth microdilution cultures, automated spectrophotometric readings of the cultures, and dose-response and endpoint determinations by means of a computer spreadsheet. Tests were based on proposed standard method M27P of the National Committee for Clinical Laboratory Standards for antifungal agents. RPMI 1640 broth with extra glucose to a final concentration of 2% gave higher and more reproducible drug-free control readings without affecting susceptibility endpoint readings. An inoculum of 8 x 10(4) yeasts per ml prepared from a carbon-limiting broth culture without further standardization was found to give optimal control readings after 48 h of incubation at 37 degrees C. For flucytosine, fluconazole, itraconazole, and ketoconazole, endpoints based on 50% growth inhibition (50% inhibitory concentration) gave the minimum variation with inoculum size and the fewest endpoint differences with RPMI 1640 medium obtained from two different suppliers. The 50% inhibitory concentration was also the optimal endpoint for fluconazole and ketoconazole susceptibilities in comparison with broth macrodilution MICs determined by the method of the National Committee for Clinical Laboratory Standards. Intralaboratory reproducibility was determined by retrospective analysis of replicate results for isolates retested at random over a 2-year period. This approach showed less favorable reproducibility than has been reported from purpose-designed, prospective antifungal susceptibility studies, but it may better reflect real-life test reproducibility. Susceptibility data for 616 clinical isolates of yeasts, representing 16 Candida and Saccharomyces spp., confirmed the tendency of Candida lusitaniae isolates to show relatively low susceptibilities to amphotericin B, the tendency of Candida krusei isolates to show low flucytosine and fluconazole susceptibilities, and the presence of some isolates in the species Candida albicans, Candida glabrata, and Candida tropicalis with low susceptibilities to azole derivative antifungal agents. The study demonstrates the value of automation and standardization in all stages of yeast susceptibility testing, from plate preparation to data analysis.

Effects of an acidic beverage (Coca-Cola) on absorption of ketoconazole

Absorption of ketoconazole is impaired in patients with achlorhydria. The purpose of this study was to determine the effectiveness of a palatable acidic beverage (Coca-Cola Classic, pH 2.5) in improving the absorption of ketoconazole in the presence of drug-induced achlorhydria. A prospective, randomized, three-way crossover design with a 1-week wash-out period between each treatment was employed. Nine healthy nonsmoking, nonobese volunteers between 22 and 41 years old were studied. Each subject was randomized to receive three treatments: (A) ketoconazole 200-mg tablet with water (control), (B) omeprazole (60 mg) followed by ketoconazole (200 mg) taken with water, and (C) omeprazole (60 mg) followed by ketoconazole (200 mg) taken with 240 ml of Coca-Cola Classic. The pH values of gastric aspirates were checked after omeprazole was administered to confirm attainment of a pH of > 6. Multiple serum samples were obtained for measurements of ketoconazole concentrations by high-pressure liquid chromatography. The mean area under the ketoconazole concentration-time curve from zero to infinity for the control treatment (17.9 +/- 13.1 mg.h/liter) was significantly greater than that for treatment B (3.5 +/- 5.1 mg.h/liter; 16.6% +/- 15.0% of control). The mean peak concentration was highest for the control treatment (4.1 +/- 1.9 micrograms/ml), for which the mean peak concentration showed a significant increase over that for treatment B. The absorption of ketoconazole was reduced in the presence of omeprazole-induced achlorhydria. However, drug absorption was significantly increased, to approximately 65% of the mean for the control treatment, when the drug was taken with an acidic beverage, such as Coca-Cola.

Fluconazole resistance due to energy-dependent drug efflux in Candida glabrata

We report on the mechanism of fluconazole resistance in Candida glabrata from a case of infection in which pre- and posttreatment isolates were available for comparison. The resistant, posttreatment isolate was cross-resistant to ketoconazole and itraconazole, in common with other azole-resistant yeasts. Resistance was due to reduced levels of accumulation of [3H]fluconazole rather than to changes at the level of ergosterol biosynthesis. Studies with metabolic or respiratory inhibitors showed that this phenomenon was a consequence of energy-dependent drug efflux, as opposed to a barrier to influx. Since energy-dependent efflux is a characteristic of multidrug resistance in bacteria, yeasts, and mammalian cells, we investigated the possibility that fluconazole resistance is mediated by a multidrug resistance-type mechanism. Benomyl, a substrate for the Candida albicans multidrug resistance protein, showed competition with fluconazole for efflux from resistance C. glabrata isolates, consistent with a common efflux mechanism for these compounds. By contrast, other standard substrates or inhibitors of multidrug resistance proteins had no effect on fluconazole efflux. In conclusion, we have identified energy-dependent efflux of fluconazole, possibly via a multidrug resistance-type transporter, as the mechanism of resistance to fluconazole in C. glabrata.

Initial use of a broth microdilution method suitable for in vitro testing of fungal isolates in a clinical microbiology laboratory

Antifungal susceptibility testing methods currently lack a standardized procedure. Many factors, such as inoculum preparation, inoculum density, medium selection, pH, incubation time and temperature, and endpoint determination, affect results. We developed a workable procedure for fungal susceptibility testing, with a microtiter method based upon modifications of the proposed guidelines from the National Committee for Clinical Laboratory Standards, using two different growth media. For this procedure, the microtiter tray is prepared as a panel of 6 drugs (amphotericin B, flucytosine, fluconazole, ketoconazole, miconazole, and itraconazole) alone and in combination with amphotericin B. Eagle's minimal essential medium and RPMI 1640 are the two growth media. Two separate susceptibility trays are inoculated for each sensitivity test, with one tray incubated at 30 degrees C and the other incubated at 35 degrees C. After 48 h of growth, results for both temperatures and both media are recorded and interpreted. The four test environments (two media each at two temperatures) provided growth for 100 of the first 104 organisms that were submitted for testing. This approach provides a workable methodology for routine antifungal susceptibility testing in a clinical microbiology laboratory setting.