Oxygen as limiting nutrient for growth of Cryptococcus neoformans

Fungicidal Activity of Recombinant Javanicin against Cryptococcus neoformans Is Associated with Intracellular Target(s) Involved in Carbohydrate and Energy Metabolic Processes

The occurrence of Cryptococcus neoformans, the human fungal pathogen that primarily infects immunocompromised individuals, has been progressing at an alarming rate. The increased incidence of infection of C. neoformans with antifungal drugs resistance has become a global concern. Potential antifungal agents with extremely low toxicity are urgently needed. Herein, the biological activities of recombinant javanicin (r-javanicin) against C. neoformans were evaluated. A time-killing assay was performed and both concentration- and time-dependent antifungal activity of r-javanicin were indicated. The inhibitory effect of the peptide was initially observed at 4 h post-treatment and ultimately eradicated within 36 to 48 h. Fungal outer surface alteration was characterized by the scanning electron microscope (SEM) whereas a negligible change with slight shrinkage of external morphology was observed in r-javanicin treated cells. Confocal laser scanning microscopic analysis implied that the target(s) of r-javanicin is conceivably resided in the cell thereby allowing the peptide to penetrate across the membrane and accumulate throughout the fungal body. Finally, cryptococcal cells coped with r-javanicin were preliminarily investigated using label-free mass spectrometry-based proteomics. Combined with microscopic and proteomics analysis, it was clearly elucidated the peptide localized in the intracellular compartment where carbohydrate metabolism and energy production associated with glycolysis pathway and mitochondrial respiration, respectively, were principally interfered. Overall, r-javanicin would be an alternative candidate for further development of antifungal agents.

Monitoring Glycolysis and Respiration Highlights Metabolic Inflexibility of Cryptococcus neoformans

Cryptococcus neoformans is a human fungal pathogen that adapts its metabolism to cope with limited oxygen availability, nutrient deprivation and host phagocytes. To gain insight into cryptococcal metabolism, we optimized a protocol for the Seahorse Analyzer, which measures extracellular acidification rate (ECAR) and oxygen consumption rate (OCR) as indications of glycolytic and respiratory activities. In doing so we achieved effective immobilization of encapsulated cryptococci, established Rotenone/Antimycin A and 2-deoxyglucose as effective inhibitors of mitochondrial respiration and glycolysis, respectively, and optimized a microscopy-based method of data normalization. We applied the protocol to monitor metabolic changes in the pathogen alone and in co-culture with human blood-derived monocytes. We also compared metabolic flux in wild-type C. neoformans, its isogenic 5-PP-IP₅/IP₇-deficient metabolic mutant kcs1∆, the sister species of C. neoformans, Cryptococcus deuterogattii/VGII, and two other yeasts, Saccharomyces cerevisiae and Candida albicans. Our findings show that in contrast to monocytes and C. albicans, glycolysis and respiration are tightly coupled in C. neoformans and C. deuterogattii, as no compensatory increase in glycolysis occurred following inhibition of respiration. We also demonstrate that kcs1∆ has reduced metabolic activity that correlates with reduced mitochondrial function. Metabolic inflexibility in C. neoformans is therefore consistent with its obligate aerobe status and coincides with phagocyte tolerance of ingested cryptococcal cells.

Epidemiological trends of cryptococcosis in Italy: Molecular typing and susceptibility pattern of Cryptococcus neoformans isolates collected during a 20-year period

In the present study clinical data and isolates from cases of cryptococcosis recorded during clinical surveys carried out in Italy from 1997 to 2016, were investigated. Molecular typing and antifungal susceptibility testing were performed in order to delineate the epidemiological trend of cryptococcosis in Italy and to define wild-type population for four different antifungal compounds. During the studied period, a total of 302 cases collected from 32 centers of 11 Italian regions were recorded. Analysis of clinical data showed a significant increase of frequency (from 7% to 38%) of cryptococcosis in human immunodeficiency virus (HIV)-negative patients primarily with hematologic malignancies and solid organ transplantations. The prevalence of the molecular types has significantly changed during the study period, showing an increase of VNIII isolates from 11% to 41% in HIV-negative patients, and a decrease of VNIV isolates from 36% to 16%. Antifungal susceptibility testing allowed us to calculate the epidemiological cut-off for flucytosine (1 mg/l), fluconazole (8 mg/l), itraconazole (0.5 mg/l), and voriconazole (0.25 mg/l). Most of the isolates were wild-type strains. Comparison of the MIC distributions according to molecular types showed that VNIV isolates had lower MICs for fluconazole and itraconazole than the VNI and VIII isolates. The current study emphasizes that the epidemiology of cryptococcosis in Italy has significantly changed over the last decades.

The CRZ1/SP1-like gene links survival under limited aeration, cell integrity and biofilm formation in the pathogenic yeast Cryptococcus neoformans

AIMS

Limited aeration has been demonstrated to cause slowdown in proliferation and delayed budding, resulting eventually in a unique unbudded G2-arrest in the obligate aerobic pathogenic yeast Cryptococcus neoformans. Also, the ability to adapt to decreased oxygen levels during pathogenesis has been identified as a virulence factor in C. neoformans. The aim of this study was to identify and characterize genes that are necessary for the proliferation slowdown and G2-arrest caused by limited aeration.

METHODS

Random mutants were prepared and screened for lack of typical slowdown of proliferation under limited aeration. The CNAG_00156.2 gene coding for a zinc-finger transcription factor was identified in mutants showing most distinctive phenotype. Targeted deletion strain and reconstituted strain were prepared to characterize and confirm the gene functions. This gene was also identified in a parallel studies as homologous both to calcineurin responsive (Crz1) and PKC1-dependent (SP1-like) transcription factors.

RESULTS

We have confirmed the role of the cryptococcal homologue of CRZ1/SP1-like transcription factor in cell integrity, and newly demonstrated its role in slowdown of proliferation and survival under reduced aeration, in biofilm formation and in susceptibility to fluconazole.

CONCLUSIONS

Our data demonstrate a tight molecular link between slowdown of proliferation during hypoxic adaptation and maintenance of cell integrity in C. neoformans and present a new role for the CRZ1 family of transcription factors in fungi. The exact positioning of this protein in cryptococcal signalling cascades remains to be clarified.

Role of actin-bundling protein Sac6 in growth of Cryptococcus neoformans at low oxygen concentration

Cryptococcus neoformans, the etiologic agent of cryptococcosis, is an obligately aerobic yeast that inhabits an environmental niche exposed to ambient air. The cell doubling time was significantly prolonged under 1% O(2) relative to that under normoxic conditions. No apparent cell cycle arrest occurred following a shift from ambient air to 1% O(2). However, yeast cells became hypersensitive to the actin monomer-sequestering agent latrunculin A at 1% O(2), indicating that proper actin function is critical for growth at low oxygen concentrations. We showed that Sac6, an actin-binding protein, played an important role in cell growth under low oxygen conditions. Sac6 colocalized with cortical actin patches and with the ring structures between mother cells and buds. Under low oxygen conditions, the sac6 deletion mutant grew poorly, and accumulation of the actin capping protein Cap1 was observed in the vacuole of the sac6Δ strain. Furthermore, endocytic processes were hampered in the sac6Δ mutant, but cell polarity and cytokinesis were not visibly disturbed. The deficiency of endocytosis in the sac6Δ strain could be rescued by 1 M sorbitol under 1% O(2), but growth remained retarded. These results suggest an absence of a direct link in C. neoformans between endocytosis and coping with the stress of low oxygen conditions. This interpretation is further supported by the observation that deletion of three conserved genes, ABP1, CRN1, and SLA2, which play important roles in endocytosis, had no effect on growth under 1% O(2). Interestingly, deletion of SAC6 in C. neoformans had no effect on virulence in mice.

Hypoxia and fungal pathogenesis: to air or not to air?

Over the last 3 decades, the frequency of life-threatening human fungal infections has increased as advances in medical therapies, solid-organ and hematopoietic stem cell transplantations, an increasing geriatric population, and HIV infections have resulted in significant rises in susceptible patient populations. Although significant advances have been made in understanding how fungi cause disease, the dynamic microenvironments encountered by fungi during infection and the mechanisms by which they adapt to these microenvironments are not fully understood. As inhibiting and preventing in vivo fungal growth are main goals of antifungal therapies, understanding in vivo fungal metabolism in these host microenvironments is critical for the improvement of existing therapies or the design of new approaches. In this minireview, we focus on the emerging appreciation that pathogenic fungi like Candida albicans, Cryptococcus neoformans, and Aspergillus fumigatus are exposed to oxygen-limited or hypoxic microenvironments during fungal pathogenesis. The implications of these in vivo hypoxic microenvironments for fungal metabolism and pathogenesis are discussed with an aim toward understanding the potential impact of hypoxia on invasive fungal infection outcomes.

Adaptation of Cryptococcus neoformans to mammalian hosts: integrated regulation of metabolism and virulence

The basidiomycete fungus Cryptococcus neoformans infects humans via inhalation of desiccated yeast cells or spores from the environment. In the absence of effective immune containment, the initial pulmonary infection often spreads to the central nervous system to result in meningoencephalitis. The fungus must therefore make the transition from the environment to different mammalian niches that include the intracellular locale of phagocytic cells and extracellular sites in the lung, bloodstream, and central nervous system. Recent studies provide insights into mechanisms of adaptation during this transition that include the expression of antiphagocytic functions, the remodeling of central carbon metabolism, the expression of specific nutrient acquisition systems, and the response to hypoxia. Specific transcription factors regulate these functions as well as the expression of one or more of the major known virulence factors of C. neoformans. Therefore, virulence factor expression is to a large extent embedded in the regulation of a variety of functions needed for growth in mammalian hosts. In this regard, the complex integration of these processes is reminiscent of the master regulators of virulence in bacterial pathogens.

Peculiar clusters of daughter cells observed in Cryptococcus neoformans grown in sealed microtiter plates

Cryptococcus neoformans was grown in 96-well microtiter plates sealed by foil which is less than 0.01 % permeable to oxygen. On day 14 of the cultivation, we observed peculiar clusters of small droplike daughter cells arranged around < or = 4 % of mother cells. The fact that most of the other cells had died indicates that few cells had been able to survive hypoxic conditions and escape the cell-cycle arrest. However, their daughters were unable to separate from them and to continue their proliferation under such conditions.

Importance of mitochondria in survival of Cryptococcus neoformans under low oxygen conditions and tolerance to cobalt chloride

Cryptococcus neoformans is an environmental fungal pathogen that requires atmospheric levels of oxygen for optimal growth. For the fungus to be able to establish an infection, it must adapt to the low oxygen concentrations in the host environment compared to its natural habitat. In order to investigate the oxygen sensing mechanism in C. neoformans, we screened T-DNA insertional mutants for hypoxia-mimetic cobalt chloride (CoCl₂)-sensitive mutants. All the CoCl₂-sensitive mutants had a growth defect under low oxygen conditions at 37°C. The majority of mutants are compromised in their mitochondrial function, which is reflected by their reduced rate of respiration. Some of the mutants are also defective in mitochondrial membrane permeability, suggesting the importance of an intact respiratory system for survival under both high concentrations of CoCl₂ as well as low oxygen conditions. In addition, the mutants tend to accumulate intracellular reactive oxygen species (ROS), and all mutants show sensitivity to various ROS generating chemicals. Gene expression analysis revealed the involvement of several pathways in response to cobalt chloride. Our findings indicate cobalt chloride sensitivity and/or sensitivity to low oxygen conditions are linked to mitochondrial function, sterol and iron homeostasis, ubiquitination, and the ability of cells to respond to ROS. These findings imply that multiple pathways are involved in oxygen sensing in C. neoformans.

Cryptococcus neoformans is an obligate aerobic fungus that requires atmospheric levels of oxygen (21%) for optimal growth. However, the fungus is able to cause life-threatening brain infections in humans, where the oxygen tension is significantly lower than 21%. To understand the pathobiology of Cryptococcus neoformans, it is important to explore the molecular mechanisms adopted by the fungus to survive under low oxygen conditions. By using cobalt chloride, a hypoxia-mimicking agent, we isolated a number of mutants that are unable to grow in the presence of 0.7 mM CoCl₂ as well as at low oxygen conditions. In this study, we show that mitochondria play an important role for C. neoformans to survive in low oxygen conditions. We demonstrate that mutants harboring mutations in the genes related to mitochondrial functions have mitochondrial membrane permeability defect and lowered respiration rate and are more sensitive to stress generating chemicals, in addition to their inability to survive at low oxygen conditions. Finally, we also show that when wild-type cells are exposed to hypoxia-mimicking cobalt chloride, expression of genes involved in respiration and iron and sterol homeostasis, as well as ubiquitination, changes significantly.

Subcutaneous cryptococcosis due to Cryptococcus diffluens in a patient with sporotrichoid lesions case report, features of the case isolate and in vitro antifungal susceptibilities

Environmental fungi, in particular primary pathogens and Cryptococcus spp. can be responsible for skin lesions mimicking sporotrichosis. In this paper, we report a case of subcutaneous cryptococcosis in an apparently healthy, young male patient due to a non-C. neoformans Cryptococcus species, C. diffluens. The isolate showed in vitro phenotypic switching that may affect virulence and host inflammatory and immune responses, and in vitro resistance to amphotericin B and 5-flucytosin. This species shares several phenotypic traits with C. neoformans, and, therefore, decisive diagnosis should be based on biopsy and culturing results followed by molecular identification.

Sre1p, a regulator of oxygen sensing and sterol homeostasis, is required for virulence in Cryptococcus neoformans

Cryptococcus neoformans is an environmental pathogen requiring atmospheric levels of oxygen for optimal growth. Upon inhalation, C. neoformans disseminates to the brain and causes meningoencephalitis, but the mechanisms by which the pathogen adapts to the low-oxygen environment in the brain have not been investigated. We found that SRE1, a homologue of the mammalian sterol regulatory element-binding protein (SREBP), functions in an oxygen-sensing pathway. Low oxygen decreased sterol synthesis in C. neoformans and triggered activation of membrane-bound Sre1p by the cleavage-activating protein, Scp1p. Microarray and Northern blot analysis demonstrated that under low oxygen, Sre1p activates genes required for ergosterol biosynthesis and iron uptake. Consistent with these regulatory functions, sre1Delta cells were hypersensitive to azole drugs and failed to grow under iron-limiting conditions. Importantly, sre1Delta cells failed to produce fulminating brain infection in mice. Our in vitro data support a model in which Sre1p is activated under low oxygen leading to the upregulation of genes required for sterol biosynthesis and growth in a nutrient-limiting environment. Animal studies confirm the importance of SRE1 for C. neoformans to adapt to the host environment and to cause fatal meningoencephalitis, thereby identifying the SREBP pathway as a therapeutic target for cryptococcosis.

Cobalt chloride, a hypoxia-mimicking agent, targets sterol synthesis in the pathogenic fungus Cryptococcus neoformans

We investigated the effects of the hypoxia-mimetic CoCl2 in the pathogenic fungus Cryptococcus neoformans and demonstrated that CoCl2 leads to defects in several enzymatic steps in ergosterol biosynthesis. Sterol defects were amplified in cells lacking components of the Sre1p-mediated oxygen-sensing pathway. Consequently, Sre1p and its binding partner Scp1p were essential for growth in the presence of CoCl2. Interestingly, high copies of a single gene involved in ergosterol biosynthesis, ERG25, rescued this growth defect. We show that the inhibitory effect of CoCl2 on scp1Delta and sre1Delta cells likely resulted from either an accumulation of non-viable methylated sterols or a decrease in the amount of ergosterol. Similar findings were also observed in the ascomycetous yeast, Schizosaccharomyces pombe, suggesting that the effects of CoCl2 on the Sre1p-mediated response are conserved in fungi. In addition, gene expression analysis revealed limited overlap between Sre1p-dependant gene activation in the presence of CoCl2 and low oxygen. The majority of genes similarly affected by both CoCl2 and low oxygen were involved in ergosterol synthesis and in iron/copper transport. This article identifies the Sre1p pathway as a common mechanism by which yeast cells sense and adapt to changes in both CoCl2 concentrations and oxygen levels.

Rates of antifungal resistance among Spanish clinical isolates of Cryptococcus neoformans var. neoformans

OBJECTIVES

Activities in vitro of six antifungal agents were tested against a collection of 317 Cryptococcus neoformans var. neoformans clinical isolates.

METHODS

The procedure described in document 7.1 by the European Committee on Antibiotic Susceptibility Testing with minor modifications was employed.

RESULTS

Amphotericin B, itraconazole, voriconazole and ravuconazole exhibited a potent activity with geometric mean (GM) MICs under 0.26 mg/L. The GM MIC of flucytosine was 7.33 mg/L and that of fluconazole was 4.16 mg/L. The rates of antifungal resistance were 5.3% for amphotericin B, 0.9% for voriconazole and 3.1% for ravuconazole. Fifteen point eight per cent of strains had itraconazole MICs > or = 1 mg/L, and 46% of strains had flucytosine MICs > or = 8 mg/L. Fluconazole susceptibility (MIC < or = 8 mg/L) stood at 53.4%.

CONCLUSIONS

The percentage of fluconazole susceptibility was significantly lower than that in other surveys. Cross-resistance to itraconazole was common (33.8%) but almost the whole collection was susceptible to voriconazole and ravuconazole. These results should be confirmed with prospective and population-based surveillance programmes.

Oxygen transfer phenomena in 48-well microtiter plates: determination by optical monitoring of sulfite oxidation and verification by real-time measurement during microbial growth

Oxygen limitation is one of the most frequent problems associated with the application of shaking bioreactors. The gas-liquid oxygen transfer properties of shaken 48-well microtiter plates (MTPs) were analyzed at different filling volumes, shaking diameters, and shaking frequencies. On the one hand, an optical method based on sulfite oxidation was used as a chemical model system to determine the maximum oxygen transfer capacity (OTR(max)). On the other hand, the Respiration Activity Monitoring System (RAMOS) was applied for online measurement of the oxygen transfer rate (OTR) during growth of the methylotropic yeast Hansenula polymorpha. A proportionality constant between the OTR(max) of the biological system and the OTR(max) of the chemical system were indicated from these data, offering the possibility to transform the whole set of chemical data to biologically relevant conditions. The results exposed "out of phase" shaking conditions at a shaking diameter of 1 mm, which were confirmed by theoretical consideration with the phase number (Ph). At larger shaking diameters (2-50 mm) the oxygen transfer rate in MTPs shaken at high frequencies reached values of up to 0.28 mol/L/h, corresponding to a volumetric mass transfer coefficient (k(L)a) of 1,600 1/h. The specific mass transfer area (a) increases exponentially with the shaking frequency up to values of 2,400 1/m. On the contrary, the mass transfer coefficient (k(L)) is constant at a level of about 0.15 m/h over a wide range of shaking frequencies and shaking diameters. However, at high shaking frequencies, when the complete liquid volume forms a thin film on the cylindric wall of the well, the mass transfer coefficient (k(L)) increases linearly to values of up to 0.76 m/h. Essentially, the present investigation demonstrates that the 48-well plate outperforms the 96-well MTP and shake flasks at widely used operating conditions with respect to oxygen supply. The 48-well plates emerge, therefore, as an excellent alternative for microbial cultivation and expression studies combining the advantages of both the high-throughput 96-well MTP and the classical shaken Erlenmeyer flask.

Cryptococcus neoformans gene expression during experimental cryptococcal meningitis

Cryptococcus neoformans, an encapsulated basidiomycete fungus of medical importance, is capable of crossing the blood-brain barrier and causing meningitis in both immunocompetent and immunocompromised individuals. To gain insight into the adaptation of the fungus to the host central nervous system (CNS), serial analysis of gene expression (SAGE) was used to characterize the gene expression profile of C. neoformans cells recovered from the CNS of infected rabbits. A SAGE library was constructed, and 49,048 tags were sequenced; 16,207 of these tags were found to represent unique sequences or tag families. Of the 304 most-abundant tags, 164 were assigned to a putative gene for subsequent functional grouping. The results (as determined according to the number of tags that identified genes encoding proteins required for these functions) indicated that the C. neoformans cells were actively engaged in protein synthesis, protein degradation, stress response, small-molecule transport, and signaling. In addition, a high level of energy requirement of the fungal cells was suggested by a large number of tags that matched putative genes for energy production. Taken together, these findings provide the first insight into the transcriptional adaptation of C. neoformans to the host environment and identify the set of fungal genes most highly expressed during cerebrospinal fluid infection.

Susceptibility testing of fungi--current status and open questions

The increase of fungal infections and the improvement of therapeutical options demand reliable antifungal susceptibility testing. In vitro susceptibility testing of fungi--in contrast to bacteria--is not yet established as a routine method. The NCCIS (National Committee for Clinical Laboratory Standards) guidelines for susceptibility testing of yeasts (and proposed for hyphomycetes) are most important for standardization. Meanwhile, essential parts of this test procedure are accepted, but it should still be improved. The concept of using only one test medium for all drugs and test organisms is not realized so far. There are also some test situations that prevent the NCCLS standard from being applied. Based on our experience, this article describes the NCCLS methods and their modifications. It places emphasis on lipophilic drugs showing controversies despite standardization. Furthermore, the prediction of MICs on the clinical outcome is discussed. Since there are some pitfalls in testing antifungals, this should be done in experienced laboratories only. The MIC has to be regarded as only one, but an important, factor in the management of fungal diseases. Host-, drug-, and pathogen-specific data should be considered simultaneously.

Flucytosine and cryptococcosis: which in vitro test is the best predictor of outcome?

The combination of flucytosine and amphotericin B is first choice treatment for active cryptococcosis. Because of innate or acquired resistance of Cryptococcus neoformans to flucytosine, in vitro testing is mandatory. Yeast nitrogen base (YNB) at pH 7.0 is the recommended medium for the broth microdilution test (NCCLS M27-A) and for the E-test. In order to verify if minimum inhibitory concentrations (MICs) were able to predict treatment outcome, the susceptibility of 24 isolates from 21 patients treated with flucytosine alone or in combination was tested by the broth microdilution, agar dilution and E-test using YNB either at pH 7.0 or at pH 5.4. Only those MICs obtained on YNB pH 5.4 proved to correlate with treatment outcome. The present study suggests that in vitro susceptibility to flucytosine of C. neoformans isolates should be evaluated on YNB pH 5.4 and the test should be standardized accordingly.

Present status of the detection of antifungal resistance: the perspective from both sides of the ocean

The NCCLS reference methodology for antifungal susceptibility testing is a new milestone of the evolution of medical mycology. The use of this methodology however, is not problem-free. At present, major limitations are a trailing phenomenon with azoles, unreliable detection of resistance to amphotericin B, poor growth of some organisms and unpractical procedures for the clinical laboratory. Herein a overview of NCCLS guidelines for yeasts and filamentous fungi is presented. Likewise, a review of studies conducted trying to overcome the limitations of reference procedures is also included. Several alternative approaches are reviewed as alternative media, inoculum size and incubation time. Modifications of reading procedure and endpoint determination are also evaluated. Agar diffusion methods and other methods for susceptibility testing are cited. Finally, we discuss the data on correlation of the in vitro results with the in vivo activity.

Timed-kill curves for Cryptococcus neoformans isolated from patients with AIDS

Infection with Cryptococcus neoformans is an increasing problem in immunocompromised patients, particularly those with acquired immune deficiency syndrome (AIDS). Amphotericin B and fluconazole are currently acceptable therapies for cryptococcal meningitis; however, their effects remain suboptimal and recurrence or treatment failure is still a problem. Antifungal susceptibility testing may be an important tool for guiding therapy, but for C. neoformans, a reliable method is still not available. This retrospective study evaluated minimal inhibitory concentration (MIC) for amphotericin B and fluconazole, and minimal fungicidal concentration (MFC) and timed-kill curves for amphotericin B against 16 clinical isolates of C. neoformans obtained from AIDS patients with cryptococcal meningitis. No correlation between clinical outcome and MIC was observed for amphotericin B. In selected cases, the MFC seemed to be a better predictor of outcome than MIC. In this study, amphotericin B timed-kill curves appeared to show a correlation with clinical outcome of the 16 patients with AIDS-associated cryptococcal meningitis. These in vitro tests must be further evaluated in prospective studies to confirm their potential usefulness for guiding cryptococcal meningitis therapy.

Influence of shaking on antifungal susceptibility testing of Cryptococcus neoformans: a comparison of the NCCLS standard M27A medium, buffered yeast nitrogen base, and RPMI-2% glucose

Cryptococcus neoformans is a nonfermentative yeast that requires oxygen for growth. The shaking of culture media achieves good oxygenation, promoting the growth of cryptococci. In this study, three test media (RPMI 1640, RPMI 1640-2% glucose, and buffered yeast nitrogen base ¿BYNB) recommended in the National Committee for Clinical Laboratory Standards M27A standard were examined. Growth abilities and minimum inhibitory concentrations (MICs) in microplates incubated at 35 degrees C for 48 h were determined. The results indicated that shaking and an inoculum size of 10(5) CFU/ml yielded optimal growth of this yeast. Compared to RPMI 1640, supplementation of RPMI 1640 with 2% glucose did not significantly improve growth of C. neoformans and resulted in an 8.7-h delay of exponential growth. Cryptococcal growth in RPMI 1640 at 24 h was notably better than that in RPMI-2% glucose, although by 48 h the growths were comparable. The MIC range of amphotericin B observed for the C. neoformans strains grown in RPMI 1640 with or without glucose was too narrow to allow the separation of susceptible and resistant strains based on clinical outcome. The widest ranges of MICs of flucytosine and fluconazole were obtained with BYNB. This work demonstrates the need for a new antifungal susceptibility test for C. neoformans.

Modified agar dilution susceptibility testing method for determining in vitro activities of antifungal agents, including azole compounds

In vitro activities of antifungal agents, including azole compounds, against yeasts were easily determined by using RPMI-1640 agar medium and by incubating the plates in the presence of 20% CO2. The end point of inhibition was clear by this method, even in the case of azole compounds, because of the almost complete inhibition of yeast growth at high concentrations which permitted weak growth of some Candida strains by traditional methods. MICs obtained by the agar dilution method were similar to those obtained by the broth dilution method proposed by the National Committee for Clinical Laboratory Standards.

Persistence, replacement, and microevolution of Cryptococcus neoformans strains in recurrent meningitis in AIDS patients

Six separate human immunodeficiency virus-positive patients with cryptococcal meningitis were each found to have been infected with a unique strain of Cryptococcus neoformans on the basis of genomic DNA finger-printing analysis with the microsatellite sequence-containing oligonucleotide probe (GGAT)4 and by random amplification of polymorphic DNA. Two patients (A and B) experienced a recurrent episode of infection. Between 12 and 16 single-colony isolates recovered from primary isolation media (> 50% of C. neoformans colonies recovered) from cerebrospinal fluid specimens were fingerprinted from both patients during each episode. The fingerprints of both isolate collections from patient B were very similar, although minor polymorphisms were evident in both sets of profiles. The fingerprints of the isolate collection from the initial episode of infection in patient A were also identical to each other, apart from minor polymorphisms, but they were clearly different from the corresponding profiles of the isolate collection from the recurrent episode, the latter of which were completely identical, apart from minor polymorphisms in a single isolate. Furthermore, prolonged storage and in vitro subculture of the isolates did not alter the fingerprint profiles. These results provided convincing evidence that patients A and B were each infected with a single C. neoformans strain during each episode of infection and that in patient B, the same strain persisted and caused both episodes, while in patient A, a different strain was responsible for each episode. The prevalence of polymorphisms in multiple single-colony isolates from both patients also suggested that C. neoformans populations may undergo microevolution.

Effect of media on growth rate and susceptibility testing of Cryptococcus neoformans

The effect of four media or media combinations on the growth and the in vitro susceptibility to amphotericin B, 5-fluorocytosine, fluconazole and itraconazole of 51 isolates of Cr. neoformans was studied. The drug concentration producing a 50% decrease in OD405 (IC50) was determined in microtiter format. The following MOPS buffered media or media combinations (antifungal drug diluent/inoculum diluent) were used: RPMI 1640 (RPMI)/RPMI, Yeast nitrogen base (YNB)/YNB, RPMI/YNB and RPMI/High resolution broth. Amphotericin B was further tested in M3 broth in the microdilution format and on RPMI agar with the E-test. Growth rates (OD405) were higher in YNB, RPMI/YNB, RPMI/HR and M3 as compared to RPMI alone. After 48 h of incubation, IC50 values obtained with RPMI alone and with RPMI/YNB correlated within two dilutions for 98, 95, 95 and 100% of test strains with amphotericin B, 5-fluorocytosine,fluconazole and itraconazole respectively. The E-test provided the widest range of IC values with amphotericin B. Growth of Cr. neoformans can be enhanced in susceptibility tests using microtiter plates with drugs diluted in RPMI by preparing the inoculum in YNB. However, when using spectrophotometric endpoint determinations, sufficient growth is obtainable with most isolates for test interpretation at 48 h in RPMI alone.

[Controversies in the standardization of susceptibility testing on yeasts to azole antimycotics]

Due to the different physical-chemical conditions of the therapeutical azoles it is necessary to choose an adequate testing procedure. In the group of azoles caused by its hydrophilia fluconazole susceptibility testing can be handled easily. However it is not possible to take the same test conditions for itraconazole as for fluconazole due to the extreme high hydrophobicity of itraconazole. The current recommendations of NCCLS should be considering these problems. Therefore it is necessary to standardize susceptibility testing for all azoles possible.