Search tips
Search criteria

Results 1-25 (68)

Clipboard (0)

Select a Filter Below

more »
Year of Publication
more »
Document Types
1.  Death by Edible Mushroom: First Report of Volvariella volvacea as an Etiologic Agent of Invasive Disease in a Patient following Double Umbilical Cord Blood Transplantation▿  
Journal of Clinical Microbiology  2010;48(11):4329-4332.
We describe a case of invasive fungal infection caused by Volvariella volvacea following double umbilical cord blood transplantation (UCBT). Although infections caused by several mushroom species have been documented, we believe this to be the first published report of invasive infection with Volvariella volvacea, an edible mushroom belonging to Agaricales.
PMCID: PMC3020845  PMID: 20826647
2.  Heteroresistance of Cryptococcus gattii to Fluconazole▿  
We analyzed 71 clinical and environmental Cryptococcus gattii strains that had been isolated before or after the advent of azole antifungals to determine their level of heteroresistance to fluconazole (LHF). All strains of C. gattii manifested heteroresistance, with LHFs that ranged between 4 μg/ml and 32 μg/ml. A considerably higher proportion of the C. gattii strains (86%) than Cryptococcus neoformans strains (46%) exhibited LHFs that were ≥16 μg/ml. No significant correlation was observed between the molecular type or serotypes of strains and their respective LHF. The strains which expressed a higher LHF were also more resistant to xenobiotics than the strains with a low LHF, and the level of resistance to xenobiotics was significantly higher than that reported for C. neoformans. The heteroresistant subpopulation, whose level of drug resistance had been raised in a stepwise manner to 64 μg/ml, reverted to the original LHF upon daily transfers in drug-free medium. Importantly, the strains with high LHFs were significantly more virulent than those with low LHFs. Since all the clinical isolates that had not been exposed to azole drugs as well as the environmental strains manifested heteroresistance to fluconazole, heteroresistance of C. gattii to azoles is an intrinsic mechanism as in C. neoformans and is associated with the strain's virulence.
PMCID: PMC2876399  PMID: 20385871
3.  Neosartorya udagawae (Aspergillus udagawae), an Emerging Agent of Aspergillosis: How Different Is It from Aspergillus fumigatus?▿  
Journal of Clinical Microbiology  2009;48(1):220-228.
A recent report on several cases of invasive aspergillosis caused by Neosartorya udagawae suggested distinctive patterns of disease progression between N. udagawae and Aspergillus fumigatus. This prompted us to characterize N. udagawae in comparison to A. fumigatus. Our findings showed that both species exist in two mating types at similar ratios and produce gliotoxin. However, the thermotolerance of the two species differs: while A. fumigatus is able to grow at 55°C but not at 10°C, N. udagawae is able to grow at 10°C but fails to grow at >42°C. Furthermore, compared to A. fumigatus, the conidia of N. udagawae require longer incubation periods to germinate at 37°C and are more susceptible to neutrophil attack as well as hydrogen peroxide; N. udagawae is also less virulent in gp91phox−/− mice. These findings suggest that growth and susceptibility to the host response might account for the reduced virulence of N. udagawae and the subtle distinction in the progression of the disease caused by the two species.
PMCID: PMC2812273  PMID: 19889894
4.  The Presence of Capsule in Cryptococcus neoformans Influences the Gene Expression Profile in Dendritic Cells during Interaction with the Fungus▿ †  
Infection and Immunity  2008;76(4):1581-1589.
The aim of this investigation was to study the effect of polysaccharide capsule on the gene expression in dendritic cells (DC) during their interaction with Cryptococcus neoformans. To this end, we used an encapsulated virulent strain of C. neoformans and a cap59 gene-disrupted acapsular avirulent strain derived from the same genetic background. DC were exposed to encapsulated and acapsular C. neoformans strains for 4 h and 18 h, and their transcriptional profiles were analyzed using the Affymetrix mouse gene chip U74Av2. A large number of DC genes were up-regulated after treatment with the acapsular strain. In particular, we observed the up-regulation of the genes involved in DC maturation, such as cell surface receptors, cytokines, and chemokines (interleukin-12 [IL-12], IL-2, IL-1α, IL-1β, IL-6, IL-10, tumor necrosis factor alpha, CCR7, CCL17, CCL22, CCL3, CCL4, CCL7, and CXCL10), membrane proteins, and the genes involved in antigen processing and presentation as well as cell cycle or apoptosis. The chemokine gene expression data were confirmed by real-time reverse transcription-PCR, while the expression of cytokine genes was correlated with their secretion. A completely different pattern of gene expression was observed for DC treated with an encapsulated strain of C. neoformans. In particular, no significant induction was observed in the expression of the genes mentioned above. Moreover, a number of genes, such as those coding for chemokines, were down-regulated. These results suggest that the polysaccharide capsule shrouding the cell wall of C. neoformans plays a fundamental role in inducing DC response, highlighting the molecular basis of the true nature of immune silencing exerted by capsular material.
PMCID: PMC2292858  PMID: 18250173
5.  CPS1, a Homolog of the Streptococcus pneumoniae Type 3 Polysaccharide Synthase Gene, Is Important for the Pathobiology of Cryptococcus neoformans  
Infection and Immunity  2006;74(7):3930-3938.
The polysaccharide capsule is known to be the major factor required for the virulence of Cryptococcus neoformans. We have cloned and characterized a gene, designated CPS1, that encodes a protein containing a glycosyltransferase moiety and shares similarity with the type 3 polysaccharide synthase encoded by the cap3B gene of Streptococcus pneumoniae. Cps1p also shares similarity with hyaluronan synthase of higher eukaryotes. Deletion of the CPS1 gene from a serotype D strain of C. neoformans resulted in a slight reduction of the capsule size as observed by using an India ink preparation. The growth at 37°C was impaired, and the ability to associate with human brain endothelial cells in vitro was also significantly reduced by the deletion of CPS1. Using site-specific mutagenesis, we showed that the conserved glycosyltransferase domains are critical for the ability of the strain to grow at elevated temperatures. A hyaluronan enzyme-linked immunosorbent assay method demonstrated that CPS1 is important for the synthesis of hyaluronan or its related polysaccharides in C. neoformans. Comparisons between the wild-type and the cps1Δ strains, using three different transmission electron microscopic methods, indicated that the CPS1 gene product is involved in the composition or maintenance of an electron-dense layer between the outer cell wall and the capsule. These and the virulence studies in a mouse model suggested that the CPS1 gene is important in the pathobiology of C. neoformans.
PMCID: PMC1489683  PMID: 16790766
6.  Agrobacterium tumefaciens-Mediated Transformation of Aspergillus fumigatus: an Efficient Tool for Insertional Mutagenesis and Targeted Gene Disruption 
Agrobacterium tumefaciens was used to transform Aspergillus fumigatus by either random or site-directed integration of transforming DNA (T-DNA). Random mutagenesis via Agrobacterium tumefaciens-mediated transformation (ATMT) was accomplished with T-DNA containing a hygromycin resistance cassette. Cocultivation of A. fumigatus conidia and Agrobacterium (1:10 ratio) for 48 h at 24°C resulted in high frequencies of transformation (>100 transformants/107 conidia). The majority of transformants harbored a randomly integrated single copy of T-DNA and were mitotically stable. We chose alb1, a polyketide synthase gene, as the target gene for homologous integration because of the clear phenotype difference between the white colonies of Δalb1 mutant strains and the bluish-green colonies of wild-type strains. ATMT with a T-DNA-containing alb1 disruption construct resulted in 66% albino transformants. Southern analysis revealed that 19 of the 20 randomly chosen albino transformants (95%) were disrupted by homologous recombination. These results suggest that ATMT is an efficient tool for transformation, random insertional mutagenesis, and gene disruption in A. fumigatus.
PMCID: PMC1082565  PMID: 15812003
7.  Cryptococcus neoformans CAP59 (or Cap59p) Is Involved in the Extracellular Trafficking of Capsular Glucuronoxylomannan 
Eukaryotic Cell  2004;3(2):385-392.
Several genes are essential for Cryptococcus neoformans capsule synthesis, but their functions are unknown. We examined the localization of glucuronoxylomannan (GXM) in strain B-3501 and in cap59 mutants B-4131 and C536. Wild-type strain B-3501 showed a visible capsule by India ink staining and immunofluorescence with anticapsular monoclonal antibodies (MAbs) 12A1 and 18B7. B-4131, a mutant containing a missense mutation in CAP59, showed no capsule by India ink staining but revealed the presence of capsular polysaccharide on the cell surface by immunofluorescence. The cap59 gene deletion mutant (C536), however, did not show a capsule by either India ink staining or immunofluorescence. Analysis of cell lysates for GXM by enzyme-linked immunosorbent assay revealed GXM in C536 samples. Furthermore, the epitopes recognized by MAbs 12A1, 2D10, 13F1, and 18B7 were each detected in the cytoplasm of all strains by immunogold electron microscopy, although there were differences in location consistent with differences in epitope synthesis and/or transport. In addition, the cells of B-3501 and B-4131, but not those of the cap59 deletant, assimilated raffinose or urea. Hence, the missense mutation of CAP59 in B-4131 partially hampered the trafficking of GXM but allowed the secretion of enzymes involved in hydrolysis of raffinose or urea. Furthermore, the cell diameter and volume for strain C536 are higher than those for strain B-3501 or B-4131 and may suggest the accumulation of cellular material in the cytoplasm. Our results suggest that CAP59 is involved in capsule synthesis by participating in the process of GXM (polysaccharide) export.
PMCID: PMC387637  PMID: 15075268
8.  Importance of a Developmentally Regulated Pheromone Receptor of Cryptococcus neoformans for Virulence  
Infection and Immunity  2003;71(9):4953-4960.
Cryptococcus neoformans is the etiologic agent of cryptococcosis. Two mating types exist in this fungus, MATα and MATa. The CPRa gene of C. neoformans is a MATa strain-specific gene and encodes a putative seven-transmembrane domain pheromone receptor. Unlike the other reported fungal pheromone receptors, CPRa shows functional diversity. Deletion of CPRa drastically affects mating efficiency but does not abolish mating. CPRa expression is developmentally regulated and is not affected by deletion of the transcriptional regulator STE12a. The expression of CPRa is markedly increased by shifting cultures from liquid to solid media. CPRa also plays a significant role in virulence. Δcpra cells produce smaller capsules in the brains of mice than the wild-type cells, and the mice infected with Δcpra survive significantly longer than those receiving the wild-type strain. Our results suggest that the MATa pheromone receptor of C. neoformans is not only required for mating but also important for survival and growth of the fungus in host tissue.
PMCID: PMC187348  PMID: 12933837
9.  Mapping of the Cryptococcus neoformans MATα Locus: Presence of Mating Type-Specific Mitogen-Activated Protein Kinase Cascade Homologs 
Journal of Bacteriology  2000;182(21):6222-6227.
In this study we investigated the relationship between the MATα locus of Cryptococcus neoformans and several MATα-specific mitogen-activated protein (MAP) kinase signal transduction cascade genes, including STE12α, STE11α, and STE20α. To resolve the location of the genes, we screened a cosmid library of the MATα strain B-4500 (JEC21), which was chosen for the C. neoformans genome project. We isolated several overlapping cosmids spanning a region of about 71 kb covering the entire MATα locus. It was found that STE12α, STE11α, and STE20α are imbedded within the locus rather than closely linked to the locus. Furthermore, three copies of MFα, the mating type α-pheromone gene, a MATα-specific myosin gene, and a pheromone receptor (CPRα) were identified within the locus. We created a physical map, based on the restriction enzyme BamHI, and identified both borders of the MATα locus. The MATα locus of C. neoformans is approximately 50 kb in size and is one of the largest mating type loci reported among fungi with a one-locus, two-allele mating system.
PMCID: PMC94759  PMID: 11029445
10.  Cryptococcus neoformans STE12α Regulates Virulence but Is Not Essential for Mating 
The Cryptococcus neoformans STE12α gene, a homologue of Saccharomyces cerevisiae STE12, exists only in mating type (MAT)α cells. In S. cerevisiae, STE12 was required for mating and filament formation. In C. neoformans, haploid fruiting on filament agar required STE12α. The ability to form hyphae, however, was not affected by deletion of STE12α when convergently growing MATa strains were present. Furthermore, ste12α disruptants were fertile when mated with MATa strains, albeit with reduced mating frequency. Most importantly, the virulence of a ste12α disruptant of serotype D strain was significantly reduced in a mouse model. When the ste12α locus was reconstituted with the wild-type allele by cotransformation, virulence was restored. Histopathological analysis demonstrated a reduction in capsular size of yeast cells, less severe cystic lesions, and stronger immune responses in meninges of mice infected with ste12α cells than those of mice infected with STE12α cells. Using reporter gene constructs, we found that STE12α controls the expression of several phenotypes known to be involved in virulence, such as capsule and melanin production. These results demonstrate a clear molecular link between mating type and virulence in C. neoformans.
PMCID: PMC2195848  PMID: 10704467
haploid fruiting; mating assay; STE12; cotransformation; virulence factor
11.  Temperature-Sensitive Strain of Cryptococcus neoformans Producing Hyphal Elements in a Feline Nasal Granuloma 
Journal of Clinical Microbiology  2000;38(2):926-928.
We report the isolation of a temperature-sensitive, serotype A, mating type α strain of Cryptococcus neoformans from a case of nasal cryptococcosis in a cat. The strain grew extremely slowly at 35°C and failed to grow at 37°C in vitro. Histopathological sections of the infected tissue revealed yeast cells producing hyphae up to several hundred micrometers in length, in addition to numerous encapsulated yeast cells typical of C. neoformans. The cultures grown on yeast extract-peptone-glucose agar at 35°C also produced some yeast cells with germ tube-like hyphal elements up to 100 μm in length.
PMCID: PMC86250  PMID: 10655419
12.  A Developmentally Regulated Gene Cluster Involved in Conidial Pigment Biosynthesis in Aspergillus fumigatus 
Journal of Bacteriology  1999;181(20):6469-6477.
Aspergillus fumigatus, a filamentous fungus producing bluish-green conidia, is an important opportunistic pathogen that primarily affects immunocompromised patients. Conidial pigmentation of A. fumigatus significantly influences its virulence in a murine model. In the present study, six genes, forming a gene cluster spanning 19 kb, were identified as involved in conidial pigment biosynthesis in A. fumigatus. Northern blot analyses showed the six genes to be developmentally regulated and expressed during conidiation. The gene products of alb1 (for “albino 1”), arp1 (for “aspergillus reddish-pink 1”), and arp2 have high similarity to polyketide synthases, scytalone dehydratases, and hydroxynaphthalene reductases, respectively, found in the dihydroxynaphthalene (DHN)-melanin pathway of brown and black fungi. The abr1 gene (for “aspergillus brown 1”) encodes a putative protein possessing two signatures of multicopper oxidases. The abr2 gene product has homology to the laccase encoded by the yA gene of Aspergillus nidulans. The function of ayg1 (for “aspergillus yellowish-green 1”) remains unknown. Involvement of the six genes in conidial pigmentation was confirmed by the altered conidial color phenotypes that resulted from disruption of each gene in A. fumigatus. The presence of a DHN-melanin pathway in A. fumigatus was supported by the accumulation of scytalone and flaviolin in the arp1 deletant, whereas only flaviolin was accumulated in the arp2 deletants. Scytalone and flaviolin are well-known signature metabolites of the DHN-melanin pathway. Based on DNA sequence similarity, gene disruption results, and biochemical analyses, we conclude that the 19-kb DNA fragment contains a six-gene cluster which is required for conidial pigment biosynthesis in A. fumigatus. However, the presence of abr1, abr2, and ayg1 in addition to alb1, arp1, and arp2 suggests that conidial pigment biosynthesis in A. fumigatus is more complex than the known DHN-melanin pathway.
PMCID: PMC103784  PMID: 10515939
13.  Isolation, Characterization, and Localization of a Capsule-Associated Gene, CAP10, of Cryptococcus neoformans 
Journal of Bacteriology  1999;181(18):5636-5643.
Cryptococcus neoformans is a pathogenic fungus which most commonly affects the central nervous system and causes fatal meningoencephalitis primarily in patients with AIDS. This fungus produces a thick extracellular polysaccharide capsule which is well recognized as a virulence factor. Here, we describe the isolation and characterization of a novel gene, CAP10, which is required for capsule formation. Complementation of the acapsular cap10 mutant produced an encapsulated strain and the deletion of CAP10 from a wild strain resulted in an acapsular phenotype. The molecular mass of the hemagglutinin epitope-tagged Cap10p is about 73 kDa, which is similar to the size predicted from sequence analysis. When CAP10 was fused with a hybrid green fluorescent protein construct, the fluorescence signals appeared as patches in the cytoplasm. Using a reporter gene construct, we found that CAP10 was expressed at high levels in late-stationary-phase cells. In addition, we found that the expression levels of CAP10 are modulated by the transcriptional factor STE12α. Deletion of STE12α downregulated the expression levels of CAP10 while overexpression of STE12α upregulated the expression levels of CAP10. Animal model studies indicate that deletion of the CAP10 gene results in the loss of virulence, and complementation of the acapsular phenotype of cap10 restores virulence. Thus, CAP10 is required for capsule formation and virulence.
PMCID: PMC94082  PMID: 10482503
14.  Heteroresistance to Fluconazole and Voriconazole in Cryptococcus neoformans 
Cryptococcus neoformans isolates that exhibited unusual patterns of resistance to fluconazole and voriconazole were isolated from seven isolates from two different geographical regions: one isolate from an Israeli non-AIDS patient and six serial isolates from an Italian AIDS patient who had suffered six recurrent episodes of cryptococcal meningitis. Each isolate produced cultures with heterogeneous compositions in which most of the cells were susceptible, but cells highly resistant to fluconazole (MICs, ≥64 μg/ml) were recovered at a variable frequency (7 × 10−3 to 4.6 × 10−2). Evidence showed that this type of resistance is innate and is unrelated to drug exposure since the Israeli patient had never been treated with azoles or any other antimycotic agents. Analysis of clonal subpopulations of these two strains showed that they exhibited heterogeneous patterns of resistance. The number of subpopulations which grew on fluconazole or voriconazole agar declined progressively with increasing azole concentration without a sharp cutoff point. For the Italian serial isolates, the number of clonal populations resistant to fluconazole (64 μg/ml) and voriconazole (1 μg/ml) increased steadily, yielding the highest number for the isolate from the last episode. Attempts to purify a sensitive subpopulation failed, but clones highly resistant to fluconazole (100 μg/ml) and moderately resistant to voriconazole (1 μg/ml) always produced a homogeneous population of resistant cells. Upon maintenance on drug-free medium, however, the majority of the homogeneously resistant cells of these subclones lost their resistance and returned to the stable initial heteroresistant phenotype. The pattern of heteroresistance was not affected by the pH or osmolarity of the medium but was influenced by temperature. The resistance appeared to be suppressed at 35°C and was completely abolished at 40°C. Although heterogeneity in azole resistance among subpopulations of single isolates has been reported for Candida species, the transient changes in expression of resistance under different growth conditions reported here have not been observed in fungal pathogens.
PMCID: PMC89380  PMID: 10428902
15.  The Developmentally Regulated alb1 Gene of Aspergillus fumigatus: Its Role in Modulation of Conidial Morphology and Virulence 
Journal of Bacteriology  1998;180(12):3031-3038.
Aspergillus fumigatus, an important opportunistic pathogen which commonly affects neutropenic patients, produces conidia with a bluish-green color. We identified a gene, alb1, which is required for conidial pigmentation. The alb1 gene encodes a putative polyketide synthase, and disruption of alb1 resulted in an albino conidial phenotype. Expression of alb1 is developmentally regulated, and the 7-kb transcript is detected only during the conidiation stage. The alb1 mutation was found to block 1,3,6,8-tetrahydroxynaphthalene production, indicating that alb1 is involved in dihydroxynaphthalene-melanin biosynthesis. Scanning electron microscopy studies showed that the alb1 disruptant exhibited a smooth conidial surface, whereas complementation of the alb1 deletion restored the echinulate wild-type surface. Disruption of alb1 resulted in a significant increase in C3 binding on conidial surfaces, and the conidia of the alb1 disruptant were ingested by human neutrophils at a higher rate than were those of the wild type. The alb1-complemented strain producing bluish-green conidia exhibited inefficient C3 binding and neutrophil-mediated phagocytosis quantitatively similar to those of the wild type. Importantly, the alb1 disruptant had a statistically significant loss of virulence compared to the wild-type and alb1-complemented strains in a murine model. These results suggest that disruption of alb1 causes pleiotropic effects on conidial morphology and fungal virulence.
PMCID: PMC107801  PMID: 9620950
16.  Isolation of the Third Capsule-Associated Gene, CAP60, Required for Virulence in Cryptococcus neoformans 
Infection and Immunity  1998;66(5):2230-2236.
A polysaccharide capsule is one of the most important virulence factors for the pathogenic fungus Cryptococcus neoformans. We previously characterized two capsule-associated genes, CAP59 and CAP64. To further dissect the molecular mechanism of capsule synthesis, 16 acapsular mutants induced by 4-nitroquinoline-1-oxide were obtained. The acapsular phenotype of one of these mutants was complemented. The cloned gene was designated CAP60, and deletion of this newly described capsule-associated gene resulted in an acapsular phenotype. The proposed 67-kDa Cap60p contains 592 amino acids and appears to have a putative transmembrane domain close to the N terminus. DNA sequence analysis revealed that CAP60 has similarity to CAP59 at the center portion of its coding regions. Contour-clamped homogeneous electric field blot analysis suggested that these two genes are on the same chromosome. CAP60 and CAP59, however, could not be functionally substituted for each other by direct complementation or by domain swap experiments. In addition, CAP60 is closely linked to a gene which is similar to a cellulose growth-specific gene of Agaricus bisporus, CEL1. Immunogold electron microscopy studies of the epitope-tagged CAP60 gene revealed that Cap60p was primarily localized to the nuclear membrane. Animal model studies indicated that CAP60 is essential for virulence. Thus, CAP60 is required for both capsule formation and virulence.
PMCID: PMC108186  PMID: 9573112
17.  Virulence of catalase-deficient aspergillus nidulans in p47(phox)-/- mice. Implications for fungal pathogenicity and host defense in chronic granulomatous disease. 
Journal of Clinical Investigation  1998;101(9):1843-1850.
Chronic granulomatous disease (CGD) is a rare genetic disorder in which phagocytes fail to produce superoxide because of defects in one of several components of the NADPH oxidase complex. As a result, patients develop recurrent life-threatening bacterial and fungal infections. The organisms to which CGD patients are most susceptible produce catalase, regarded as an important factor for microbial pathogenicity in CGD. To test the role of pathogen-derived catalase in CGD directly, we have generated isogenic strains of Aspergillus nidulans in which one or both of the catalase genes (catA and catB), have been deleted. We hypothesized that catalase negative mutants would be less virulent than the wild-type strain in experimental animal models. CGD mice were produced by disruption of the p47(phox) gene which encodes the 47-kD subunit of the NADPH oxidase. Wild-type A. nidulans inoculated intranasally caused fatal infection in CGD mice, but did not cause disease in wild-type littermates. Surprisingly, wild-type A. nidulans and the catA, catB, and catA/catB mutants were equally virulent in CGD mice. Histopathological studies of fatally infected CGD mice showed widely distributed lesions in the lungs regardless of the presence or absence of the catA and catB genes. Similar to the CGD model, catalase-deficient A. nidulans was highly virulent in cortisone-treated BALB/c mice. Taken together, these results indicate that catalases do not play a significant role in pathogenicity of A. nidulans in p47(phox)-/- mice, and therefore raise doubt about the central role of catalases as a fungal virulence factor in CGD.
PMCID: PMC508769  PMID: 9576747
18.  A gene homologous to Saccharomyces cerevisiae SNF1 appears to be essential for the viability of Candida albicans. 
Infection and Immunity  1997;65(12):4909-4917.
The SNF1 gene of Saccharomyces cerevisiae (ScSNF1) is essential for the derepression of catabolic repression. We report here the isolation and characterization of an SNF1 homolog from Candida albicans (CaSNF1) which is apparently essential for the viability of this organism. The putative amino acid sequence of CaSNF1 has 68% identity with that of ScSNF1 and can restore the S. cerevisiae snf1 delta mutant's ability to utilize sucrose. Disruption of one of the CaSNF1 alleles resulted in morphological changes and decreased growth rates but did not modify the carbon source utilization pattern. Repetitive unsuccessful attempts to generate a snf1/snf1 homozygote by disruption of the second allele, using various vectors and approaches, suggest the lethal nature of this mutation. Integration into the second allele was possible only when a full-length functional SNF1 sequence was reassembled, further supporting this hypothesis and indicating that the indispensability of Snf1p prevented the isolation of snf1/snf1 mutants. The mutant bearing two disrupted SNF1 alleles and the SNF1 functional sequence maintained its ability to utilize sucrose and produced stellate colonies with extensive hyphal growth on agar media. It was demonstrated that in a mouse model, the virulences of this mutant and the wild-type strain are similar, suggesting that hyphal growth in vitro is not an indicator for higher virulence.
PMCID: PMC175708  PMID: 9393775
19.  Stereoselective interaction of the azole antifungal agent SCH39304 with the cytochrome P-450 monooxygenase system isolated from Cryptococcus neoformans. 
We investigated the stereoselective inhibition of growth and ergosterol biosynthesis by SCH39304 in the pathogenic fungus Cryptococcus neoformans obtained from four AIDS patients who failed fluconazole therapy and compared the results to those obtained with a wild-type strain. For all strains, the MICs of the RR isomer were approximately half those of the racemate, with the SS enantiomer showing no inhibitory activity. The 50% inhibitory concentrations for in vitro ergosterol biosynthesis correlated with the MIC data, indicating stereoselective inhibition of their target P-450 enzyme, sterol 14alpha-demethylase, as the cause of this difference. The RR enantiomer produced classical type II spectra on addition to microsomal extracts of the strains, whereas the SS enantiomer showed an absence of binding. Stereo- and regio-specific localization of N-1 substituent groups of SCH39304 within the active site of the enzyme determined the unique discrimination between its two enantiomers, and the inability to bind to sterol 14alpha-demethylase is also true of other P-450 enzymes contained in the microsomal fraction. As previously observed for other antifungal azoles, isolates obtained following failure of fluconazole therapy showed resistance to SCH39304 and its RR enantiomer. This resistance could be associated with an alteration in the sensitivity of ergosterol biosynthesis in vitro. These alterations did not cause any changes allowing the SS enantiomer to bind to the P-450 mediating sterol 14alpha-demethylation.
PMCID: PMC163941  PMID: 9210667
20.  Structure and biological activities of acapsular Cryptococcus neoformans 602 complemented with the CAP64 gene. 
Infection and Immunity  1997;65(5):1584-1592.
The extracellular polysaccharide capsule of Cryptococcus neoformans is a well-recognized virulence factor. Strain 602 is an acapsular clinical isolate of unknown serotype which has been widely used in studies of virulence and host-parasite interactions. In previous studies, strain 602 was compared with genetically unrelated strains of various serotypes because the wild-type equivalent of strain 602 was not available. We created an encapsulated strain, TYCC38-602, by transforming strain 602 with the CAP64 gene which was isolated from a serotype D strain. Serological tests and chemical analysis of the major polysaccharide capsule of TYCC38-602 indicated that strain 602 was originally derived from a serotype A strain. Restoration of the ability to produce a capsule enabled strain 602 to cause fatal infection in mice, whereas the acapsular strain 602 remained avirulent. Capsule-restored yeast cells of strain 602 activated the human complement system and bound C3 fragments in a manner that is characteristic of encapsulated cryptococci. In addition, the capsule in TYCC38-602 masked the ability of the organism to induce tumor necrosis factor alpha and subsequent nitric oxide synthase production in primed macrophage-like cells. These results indicate that the lack of capsule in strain 602 is the reason for its inability to cause fatal infection. Moreover, the acapsular phenotype accounts for differences in various biological activities of strain 602 compared to encapsulated strains. The results also indicate that the gene product of CAP64 does not contribute to serotype specificity of capsules in C. neoformans.
PMCID: PMC175178  PMID: 9125534
21.  Disruption of the SNF1 gene abolishes trehalose utilization in the pathogenic yeast Candida glabrata. 
Infection and Immunity  1996;64(12):5269-5273.
The SNF1 gene product, a serine/threonine protein kinase, is a global regulatory protein which has been isolated from several organisms. In Saccharomyces cerevisiae the SNF1 gene product is essential for the derepression of glucose repression since snf1 strains are unable to utilize sucrose, galactose, maltose, melibiose, or nonfermentable carbohydrates. Moreover, the SNF1 gene product was suggested to interact with additional regulatory pathways and to affect the expression of multiple target genes as reflected by the pleiotropic nature of the snf1 mutation. Here we report the characterization of the SNF1 homolog of Candida glabrata, a pathogenic yeast phylogenetically related to S. cerevisiae. The carbon utilization spectrum of C. glabrata is considerably narrower than that of other pathogenic yeasts, and the majority of the strains utilize solely glucose and trehalose from among 20 of the most commonly tested carbohydrates. Disruption of the C. glabrata SNF1 homolog resulted in the loss of the ability to utilize trehalose, indicating that even in an organism with such a limited carbon utilization spectrum, the regulatory mechanism governing catabolic repression is preserved.
PMCID: PMC174518  PMID: 8945576
22.  The second capsule gene of cryptococcus neoformans, CAP64, is essential for virulence. 
Infection and Immunity  1996;64(6):1977-1983.
The extracellular polysaccharide capsule produced by Cryptococcus neoformans is essential for its pathogenicity. We have isolated and characterized a gene, (AP64, which is required for capsule formation. An encapsulated strain created by complementation of the cap64 mutation produced fatal infection of mice within 25 days, while the cap64 acapsular strain was avirulent. Gene deletion of CAP64 from a wild-type strain resulted in the loss of capsule as well as virulence. Contour-clamped homogeneous electric field gel analysis indicates that CAP64 is located on chromosome III which is different from the localization of another capsule-related gene, CAP59. The nonlinkage between CAP64 and CAP59 was also supported by classical recombinational analysis. Database searches did not reveal any sequence with high similarity to CAP64. We also found that the CAP64 locus is contiguous to a convergently transcribed gene which has significant similarity to the gene encoding the yeast proteasome subunit, PRE1. The distance between the cDNA ends of these two genes is only 22 bp. This study confirms the previous molecular genetic evidence that capsule is an essential factor for the virulence of C. neoformans in the murine model.
PMCID: PMC174025  PMID: 8675296
23.  Deletion of the Candida glabrata ERG3 and ERG11 genes: effect on cell viability, cell growth, sterol composition, and antifungal susceptibility. 
Antimicrobial Agents and Chemotherapy  1995;39(12):2708-2717.
We have cloned and sequenced the structural genes encoding the delta 5,6 sterol desaturase (ERG3 gene) and the 14 alpha-methyl sterol demethylase (ERG11 gene) from Candida glabrata L5 (leu2). Single and double mutants of these genes were created by gene deletion. The phenotypes of these mutants, including sterol profiles, aerobic viabilities, antifungal susceptibilities, and generation times, were studied. Strain L5D (erg3 delta::LEU2) accumulated mainly ergosta-7,22-dien-3 beta-ol, was aerobically viable, and remained susceptible to antifungal agents but had a slower generation time than its parent strain. L5LUD (LEU2 erg11 delta::URA3) strains required medium supplemented with ergosterol and an anaerobic environment for growth. A spontaneous aerobically viable mutant, L5LUD40R (LEU erg11 delta::URA3), obtained from L5LUD (LEU2 erg11 delta::URA3), was found to accumulate lanosterol and obtusifoliol, was resistant to azole antifungal agents, demonstrated some increase in resistance to amphotericin B, and exhibited a 1.86-fold increase in generation time in comparison with L5 (leu2). The double-deletion mutant L5DUD61 (erg3 delta::LEU2 erg11 delta::URA3) was aerobically viable, produced mainly 14 alpha-methyl fecosterol, and had the same antifungal susceptibility pattern as L5LUD40R (LEU2 erg11 delta::URA3), and its generation time was threefold greater than that of L5 (leu2). Northern (RNA) analysis revealed that the single-deletion mutants had a marked increase in message for the undeleted ERG3 and ERG11 genes. These results indicate that differences in antifungal susceptibilities and the restoration of aerobic viability exist between the C. glabrata ergosterol mutants created in this study and those sterol mutants with similar genetic lesions previously reported for Saccharomyces cerevisiae.
PMCID: PMC163017  PMID: 8593007
24.  Mucormycosis caused by Rhizopus microsporus var. microsporus: cellulitis in the leg of a diabetic patient cured by amputation. 
Journal of Clinical Microbiology  1995;33(12):3341-3344.
Mucormycosis accompanied the development of bacterial infection in the leg of a diabetic African-American man. Local injury, diabetic ketoacidosis, renal insufficiency, and antimicrobial therapy were factors that contributed to the pathogenesis of the mucormycosis. The cellulitis was caused in part by Rhizopus microsporus var. microsporus and was cured by amputation. We report this unusual case of mucormycosis to emphasize the value of fungal identification, to illustrate a dramatic and successful clinical result, and to draw attention to an apparent role for bacterial infection and its treatment in the pathogenesis of mucormycosis. It is the third case report of mucormycosis in a human in which R. microsporus var. microsporus was definitively identified as the etiologic agent.
PMCID: PMC228705  PMID: 8586734
25.  Diversity of DNA fingerprints in Cryptococcus neoformans. 
Journal of Clinical Microbiology  1995;33(7):1807-1814.
DNA fingerprint patterns of 156 Cryptococcus neoformans isolates (26 AIDS patients, 46 non-AIDS patients, and 40 environmental sources) from both varieties (126 C. neoformans var. neoformans and 30 C. neoformans var. gattii isolates) and from seven countries were analyzed by using the DNA probe UT-4p. Nine and twelve distinct DNA fingerprint patterns were observed for isolates of the C. neoformans var. neoformans and var. gattii, respectively. No pattern was unique to AIDS patients, non-AIDS patients, or the environment. Pattern II was observed more often in non-AIDS patients (8 of 23) than in AIDS patients (0 of 25). Pattern V was the most prevalent pattern (42 of 82) in clinical and environmental isolates. Isolates from three AIDS patients in Burundi and Zaire exhibited patterns identical to each other but different from those of isolates collected from their houses (i.e., dust of floors, walls, etc.) or a nearby pigeon coop. DNA fingerprint stability was determined for 53 isolates from nine non-AIDS patients at different time intervals during 5 to 128 weeks of antifungal therapy. For eight patients, the fingerprint pattern was stable while the ninth may have had a mixed infection. Pattern II was observed in 4 of 9 patients, which is similar to 4 of 14 in other non-AIDS patients as reported here. In spite of the extensive pattern heterogeneity among 15 C. neoformans var. gattii isolates in Australia, the patterns observed in seven California isolates were quite different from those in Australia. Among isolates of C. neoformans var. gattii, one fingerprint pattern (designated b) was observed in several countries of the Far East. The fingerprint patterns of two of three environmental isolates from Eucalyptus camaldulensis trees in Australia were identical to those of 2 of the 12 clinical isolates from the country.
PMCID: PMC228275  PMID: 7665650

Results 1-25 (68)