Detection of antibodies to phospholipase B in patients infected with Cryptococcus neoformans by enzyme-linked immunosorbent assay (ELISA)

Secreted phospholipases are virulence factors of several fungi, including Cryptococcus neoformans. We describe for the first time the detection by ELISA of antibodies to cryptococcal phospholipase B in the serum of patients infected with C. neoformans or C. gattii. Sixty-nine sera from 25 patients with cryptococcosis, 23 patients with Candida infections and 26 with bacterial or viral infections were tested. The sensitivity of the ELISA in patients with cryptococcosis was 100% in immunocompetent hosts and 64.3% in immunosuppressed patients with cryptococcal meningitis. Absorbance readings were significantly higher in immunocompetent patients (P<0.001). Titres remained positive for up to 2 years. Positive results were noted in 10 episodes of invasive candidiasis, three patients colonised with Candida, and three cases of bacterial infection. Mean absorbance readings were significantly lower in patients with bacterial infection (P <0.001). We conclude that phospholipase B is produced in vivo during cryptococcal infection and that serum phospholipase B antibodies are a sensitive marker of present or past infection. Cross-reactivity of the ELISA with sera from patients with candidiasis indicates that common epitopes are present on cryptococcal and candidal phospholipase B, hence fungal phospholipase B may constitute a new therapeutic target.

Regulatory roles for the homeodomain and C2H2 zinc finger regions of Cryptococcus neoformans Ste12alphap

The STE12alpha gene of Cryptococcus neoformans encodes a protein containing both homeodomain and zinc finger regions. As homeodomains and zinc finger regions are important domains for the function of many transcription factors, we used site-specific mutagenesis to delineate the roles of these two domains. The homeodomain and zinc finger regions are each important for the function of Ste12alphap. DNA binding ability, mating frequency, and haploid fruiting capability were reduced in strains with mutations in the homeodomain, whereas virulence and capsule size in the mouse brain were increased. In contrast, mutations in the zinc fingers region resulted in decreased virulence, reduced capsule size in the mouse brain and decreased gene expression of capsule associated genes. In addition, phospholipase activity was increased in the zinc finger mutants. Taken together, most of the phenotypes previously observed in the ste12alpha deletion strains were reproduced in these two types of mutants. However, unlike mutations in the homeodomain/zinc finger region, complete deletion of STE12alpha caused a severe reduction in virulence and a decrease in phospholipase activity. These data suggest that region(s) other than the homeodomain and zinc finger regions of Ste12alphap contribute to the variable influences on the different phenotypes observed in C. neoformans.

Unsupervised feature dimension reduction for classification of MR spectra

We present an unsupervised feature dimension reduction method for the classification of magnetic resonance spectra. The technique preserves spectral information, important for disease profiling. We propose to use this technique as a preprocessing step for computationally demanding wrapper-based feature subset selection. We show that the classification accuracy on an independent test set can be sustained while achieving considerable feature reduction. Our method is applicable to other classification techniques, such as neural networks, support vector machines, etc.

Isolation of two molecular types of Cryptococcus neoformans var. gattii from insect frass

Cryptococcus neoformans var. gattii has regularly been the cause of serious human disease. However, the environmental sources of these infections often remain unclear. During an environmental sampling study, two different strains of C. neoformans var. gattii were isolated from fresh insect frass (order Lepidoptera; family Oecophoridae) in a shallow cavity in the bark of a living Eucalyptus tereticornis tree, one molecular type VGI and the other VGII. This is the first published report of the isolation of two different molecular types of C. neoformans var. gattii from a single source, and the third of isolation of molecular type VGII from an environmental source. The potential association with insect frass is consistent with categorising C. neoformans var. gattii within the Tremellales, containing mycoparasitic fungi.

Partial sequence analysis of the actin gene and its potential for studying the phylogeny of Candida species and their teleomorphs

The actin gene has been studied as a potential phylogenetic marker for selected members of the anamorphic genus Candida and seven related teleomorphic genera (Debaryomyces, Issatchenkia, Kluyveromyces, Saccharomyces and Pichia from the Saccharomycetaceae; Clavispora and Metschnikowia from the Metschnikowiaceae). The nucleotide sequences of 36 fungal taxa were analysed with respect to their molecular evolution and phylogenetic relationships. A total of 460 bp (47%) of the coding 979 bp were variable and 396 bp (40%) of these were found to be phylogenetically informative. Further analysis of the sequences showed that the genic G+C contents were higher than the nuclear G+C contents for most of the taxa. A strong positive correlation was found between G+C content over all codon positions and third positions. First and second codon positions were considered to be independent of the genic G+C content. The expected transition/transversion bias was detected only for third positions. Pairwise comparisons of transitional and transversional changes (substitutions) with total percentage sequence divergences revealed that the third position transitions showed no saturation for ingroup comparisons. A specific weighting scheme was set up, combining codon-position weights with change-frequency weights to enable the inclusion of distant outgroup taxa. Parsimony analyses of the investigated taxa showed four groups, three of which corresponded to major clusters that had been established previously in Candida by rDNA analysis. Interrelationships among the species groups in this heterogeneous anamorphic genus were determined. The polyphyletic origin of the selected Candida species and their close associations with several ascomycete genera were verified and known anamorph/teleomorph pairs confirmed. The actin gene was established as a valuable phylogenetic marker with the particular advantage of an unambiguous alignment.

Cryptococcomas distinguished from gliomas with MR spectroscopy: an experimental rat and cell culture study

PURPOSE

To use magnetic resonance (MR) spectroscopy to characterize clinical isolates of Cryptococcus neoformans and a glioma cell line in culture and in experimental rats.

MATERIALS AND METHODS

One- and two-dimensional hydrogen 1 MR spectra were acquired from fungi cultured in vitro (16 isolates of C neoformans, three of Candida albicans, three of Aspergillus fumigatus, three of Saccharomyces cerevisiae) and a C6 glioma cell line. Cerebral biopsy specimens were obtained from healthy rats and animals with experimental infections or gliomas (19 healthy brains, 20 cryptococcomas, and 19 gliomas). Unequivocal signal assignment was performed for cell suspensions and tissue samples by using homo- and heteronuclear two-dimensional correlation spectra.

RESULTS

MR spectra of C neoformans and cerebral cryptococcomas--but not of other fungi, healthy brains, or gliomas--were dominated by resonances from the cytosolic disaccharide alpha,alpha-trehalose. This spectral pattern was different from that of gliomas, which was dominated by lipids and an increased choline-creatine ratio, and that of healthy brain.

CONCLUSION

A remarkably high concentration of alpha,alpha-trehalose in relation to other metabolites that are visible with MR spectroscopy is diagnostic of C neoformans. Cerebral cryptococcomas are an uncommon but serious manifestation of cryptococcosis in humans. Application of these results to the noninvasive diagnosis of cerebral cryptococcomas would help reduce the risk and expense of unnecessary surgery or biopsy and expedite patient treatment.

Cryptococcosis: clinical and biological aspects

The incidence of cryptococcosis rose dramatically with the advent of the acquired immune deficiency syndrome (AIDS) epidemic in the early 1980s until the early 1990s. The frequency of cryptococcosis has been declining since mid 1990s in Europe and America due to the development of more effective antiretroviral therapy and prophylactic treatment regimens designed to prevent fungal infections. The disease, however, is still recognized as one of the most common life-threatening opportunistic fungal infections in immunocompromised patients, particularly among those infected with human immunodeficiency virus (HIV). For this reason, research interest in clinical and biological aspects of the disease remains high. In addition to previously embarked areas of research, the cryptococcal research community has taken advantage of the current sequencing technology and initiated genome sequencing of Cryptococcus neoformans var. neoformans. This review includes various areas of research interest ranging from pathobiology, biochemistry and immunology, to genomics.

Cryptococcus neoformans variety gattii

Cryptococcus neoformans var. gattii is emerging as a primary human pathogen which is distinct genetically and biochemically from C. neoformans var. neoformans. There is increasing evidence that it should be reclassified as a separate species within the Tremellales. In nature, C. n. var. gattii has been consistently isolated from decaying wood in hollows of species of the red gum group of eucalyptus trees (Eucalyptus ser. Exsertae Blakely). The role that trees play in the life-cycle of C. n. var. gattii is not known, but its association with decaying wood is suggestive of an endophytic existence, in common with other wood-rot fungi. Despite the demonstration in the laboratory of sexual reproduction between mating types oc and a of F. neoformans var. gattii, this has not been demonstrated in nature. Human cryptococcosis develops following environmental exposure and inhalation of the infectious propagule. Whether this is the basidiospore or dessicated yeast form is uncertain. The major risk factor for development of disease appears to be exposure, though there is indirect evidence that unidentified host factors may contribute to the relatively high incidence of cryptococcosis in Australian Aboriginals. The rarity of cryptococcosis due to C. n. var. gattii in immunocompromised patients remains unexplained. Virulence determinants of C. neoformans are currently the subject of intensive investigation, especially in C. n. var. neoformans. The best-characterized, major, virulence determinants in this variety, the polysaccharide capsule, products of the laccase enzyme pathway and ability to grow at physiological temperatures, contribute to its survival in the host. They are also present in C. n. var. gattii. A potential determinant of tissue invasion, secreted phospholipase B, is produced in vitro and in vivo by C. n. var. gattii. This enzyme has now been confirmed to play a role in the virulence of C. neoformans serotype A. Disease caused by C. n. var. gattii is distinguished from that due to C. n. var. neoformans by an increased incidence of cryptococcomas in lung and brain, increased neurological morbidity and a slower response to antifungal therapy. The difference in clinical presentation is predominantly due to the effect of underlying immunocompromise in patients infected with C. n. var. neoformans.

PCR fingerprinting: a convenient molecular tool to distinguish between Candida dubliniensis and Candida albicans

Candida dubliniensis was recently identified as a germ-tube- and chlamydospore-positive yeast, phenotypically and morphologically indistinguishable from the phylogenetically closely related yeast species C. albicans and its synonymized variant C. stellatoidea. The high similarity between these yeast species causes significant problems in the correct identification of C. dubliniensis in a standard clinical mycology laboratory. Polymerase chain reaction (PCR) fingerprinting was successfully applied here to distinguish between clinical isolates of the two closely related species. Microsatellite ([GACA]4) and minisatellite ([5'-GAGGGTGGCGGTTCT-3'], derived from the core-sequence of the wild-type phage M13) specific oligonucleotides were used as single primers in PCR to amplify hypervariable inter-repeat DNA sequences from 16 C. dubliniensis strains and 11 C. albicans strains. Each species, represented by its ex-type strain, could be identified by a distinct species-specific multilocus pattern, allowing identification to species level for all clinical isolates. In addition, the PCR fingerprinting generated strain-specific profiles, making this method applicable to epidemiological investigations. PCR fingerprinting using the primer M13 is proposed here as a simple, reliable and highly reproducible molecular tool to differentiate between strains of C. albicans and C. dubliniensis.

Extracellular phospholipase activity is a virulence factor for Cryptococcus neoformans

The human pathogenic fungus Cryptococcus neoformans secretes a phospholipase enzyme that demonstrates phospholipase B (PLB), lysophospholipase hydrolase and lysophospholipase transacylase activities. This enzyme has been postulated to be a cryptococcal virulence factor. We cloned a phospholipase-encoding gene (PLB1) from C. neoformans and constructed plb1 mutants using targeted gene disruption. All three enzyme activities were markedly reduced in the mutants compared with the wild-type parent. The plb1 strains did not have any defects in the known cryptococcal virulence phenotypes of growth at 37 degrees C, capsule formation, laccase activity and urease activity. The plb1 strains were reconstituted using the wild-type locus and this resulted in restoration of all extracellular PLB activities. In vivo testing demonstrated that the plb1 strain was significantly less virulent than the control strains in both the mouse inhalational model and the rabbit meningitis model. We also found that the plb1 strain exhibited a growth defect in a macrophage-like cell line. These data demonstrate that secretory phospholipase is a virulence factor for C. neoformans.

Purification and characterization of secretory phospholipase B, lysophospholipase and lysophospholipase/transacylase from a virulent strain of the pathogenic fungus Cryptococcus neoformans

Infection caused by the fungus Cryptococcus neoformans is potentially fatal. A highly active extracellular phospholipase, demonstrating phospholipase B (PLB), lysophospholipase (LPL) and lysophospholipase/transacylase (LPTA) activities, was purified to homogeneity from C. neoformans using (NH(4))(2)SO(4) fractionation, and hydrophobic-interaction, anion-exchange and gel-filtration chromatography. All three enzyme activities co-purified as a single protein with an apparent molecular mass of 70-90 kDa by SDS/PAGE and 160-180 kDa by gel filtration. The ratio of the three activities remained constant after each purification step. The amino acid composition, as well as the sequences of the N-terminus and of five internal peptide fragments were novel. The protein was an acidic glycoprotein containing N-linked carbohydrate moieties, with pI values of 5.5 and 3.5. The apparent V(max) values for PLB and LPL activities were 12.3 and 870 micromol/min per mg of protein respectively; the corresponding K(m) values were approx. 185.3 and 92.2 microM. The enzyme was active only at acidic pH (pH optimum of 4.0 for PLB and 4.0-5.0 for LPL and LPTA). Enzyme activity did not require added cations, but was inhibited by Fe(3+). LPL and LPTA activities were decreased by 0.1% (v/v) Triton X-100 to 50% of the control value. Palmitoylcarnitine (0.5 mM) inhibited PLB (97% inhibition) and LPL and LPTA activities (35% inhibition) competitively. All phospholipids except phosphatidic acid were degraded by PLB, but dipalmitoyl phosphatidylcholine and dioleoyl phosphatidylcholine were the preferred substrates. This is the first complete description of the purification and properties of a phospholipase, which may be involved in virulence, from a pathogenic fungus.

The origin of 1H NMR-visible triacylglycerol in human neutrophils. Highfatty acid environments result in preferential sequestration of palmitic acid into plasma membrane triacylglycerol

Human neutrophils incubated for 1 h in vitro with 10% commercial pooled, human serum containing high levels of free fatty acids (1141 microM) displayed a distinct lipid signal, typical of triacylglycerol, in the 1H NMR spectrum. Concurrently their plasma membrane triacylglycerol mass increased 4.6-fold with a selective rise in the content of palmitic and linoleic acids. Although qualitatively similar, these effects were much greater than those observed after incubating neutrophils with 50 microg.mL-1 of lipopolysaccharide in the presence of 10% AB serum with normal free fatty acid content (345 microM, LPS/S). Incubation of neutrophils with an artificial mixture of free fatty acids at concentrations found in commercial serum, or with the fatty acid fraction isolated from commercial serum increased the 1H NMR-detectable triacylglycerol. The signal intensity of the 1H NMR-detectable triacylglycerol depended on the triacylglycerol composition, and correlated with increased membrane triacylglycerol mass. Cellular uptake of 3H-labelled palmitic or oleic acids increased in the presence of commercial serum but not with LPS/S, with little contribution in either case to the triacylglycerol pool that increased in mass. Pulse-chase experiments demonstrated that with LPS/S and commercial serum, radiolabelled palmitic acid was preferentially incorporated into triacylglycerol located in the plasma membrane. This process could occur at the plasma membrane, as cytoplasts efficiently convert exogenous fatty acids into triacylglycerol. We propose that LPS/S and serum containing high levels of free fatty acid, important in conditions of sepsis and inflammation, may facilitate the sequestration of palmitic acid into triacylglycerol by different pathways. This triacylglycerol originates from exogenous and endogenous free fatty acids, is 1H NMR-visible, and may have a role in regulating apoptosis.

Heteronuclear NMR studies of metabolites produced by Cryptococcus neoformans in culture media: identification of possible virulence factors

The yeast, Cryptococcus neoformans var. neoformans is a major contributor to the morbidity and mortality experienced by the immunosuppressed population. With a view to providing better treatment, identification of cryptococcal virulence factors is an important goal, with most effort to date directed toward the significance of structural variations in the polysaccharide capsule. The present work describes the characterization of supernatants obtained from cryptococcal cultures. This was achieved by thorough identification of the spin systems of individual metabolites through both homonuclear and heteronuclear NMR experiments that circumvented the difficulties imposed by limited dispersion and a range of concentrations in different cultures covering more than 3 orders of magnitude. More than 30 metabolites, including amino acids, alditols, nucleosides, acetate, and ethanol, were identified by their (1)H and (13)C chemical shifts and observed long-range correlations. The possible contribution of some detected substances to the pathogenicity of Cryptococcus neoformans is discussed. Magn Reson Med 42:442-453, 1999.

Molecular typing of global isolates of Cryptococcus neoformans var. neoformans by polymerase chain reaction fingerprinting and randomly amplified polymorphic DNA-a pilot study to standardize techniques on which to base a detailed epidemiological survey

A total of 356 clinical isolates of the encapsulated basidiomycetous fungus Cryptococcus neoformans var. neoformans, obtained from Australia, Argentina, Brazil, India, Italy, New Zealand, Papua New Guinea, South Africa, Thailand and the USA, were analyzed to lay the basis for a comprehensive evaluation of the global genetic structure of C. neoformans. Two polymerase chain reaction (PCR)-based typing techniques were standardized: PCR fingerprinting using a single primer specific to minisatellite or microsatellite DNA, and randomly amplified polymorphic DNA (RAPD) analysis using two combinations of three 20- to 22-mer random primers. Previous studies showed that the resultant profiles are reproducible and stable over time. Identical results were obtained in two different laboratories and by different scientists in the same laboratory. Both typing techniques separated the isolates into four major groups (VNI and VNII, serotype A; VNIII, serotype A/D; and VNIV, serotype D). The majority (78%) of isolates belonged to VNI, compared with 18% VNII, 1% VNIII and 3% VNIV. All US isolates could be differentiated by a unique, strain-specific PCR fingerprint or RAPD pattern in contrast to most of the non-US isolates, which showed a substantially higher degree of genetic homogeneity, with some clonality, in different parts of the world. Isolates obtained from the same patient at different times and from different body sites, had identical banding patterns. Both typing techniques should provide powerful tools for epidemiological studies of medically important fungi.

Comparison of use of phenotypic and genotypic characteristics for identification of species of the anamorph genus Candida and related teleomorph yeast species

A total of 49 type and neotype isolates and 32 clinical isolates of the anamorph genus Candida and related teleomorph genera were obtained from different culture collections and clinical laboratories. Isolates were subjected to two phenotypic methods of identification, Vitek yeast biochemical card (YBC) and API ID 32C, both based on carbohydrate assimilation, and one genotypic method, PCR fingerprinting, based on the detection of DNA polymorphisms between minisatellite-specific sequences with the primer M13 (5' GAGGGTGGCGGTTCT 3'). The correct identification of a strain at the Centraalbureau voor Schimmelcultures was used as the gold standard for the identification of an isolate. When the study was restricted to species included in the respective biochemical databases, the Vitek YBC and API ID 32C systems performed adequately with positive identification rates of 87.3 and 76.8%, respectively. When uncommon species were added to the study, several of which are not included in the databases, the identification efficiencies were 76.5 and 77.5%, respectively. By comparison, all isolates were correctly identified by PCR fingerprinting, with 63 reference species profiles in the databank. Sufficient polymorphisms among the total set of banding patterns were observed, with adequate similarity in the major patterns obtained from a given species, to allow each isolate to be assigned unambiguously to a particular species. In addition, variations in minor bands allowed for differentiation to the strain level. PCR fingerprinting was found to be rapid, reproducible, and more cost-effective than either biochemical approach. Our results provide reference laboratories with an improved identification method for yeasts based on genotypic rather than phenotypic markers.

Leptospirosis presenting as a haemorrhagic fever in a traveller from Africa

Leptospirosis is usually a mild illness, although the severity of clinical manifestations may vary between the serovars of leptospires. In May 1993, a 48-year-old man from Ghana presented with severe icteric leptospirosis, initially managed as viral haemorrhagic fever. The causative serovar, bataviae, had not been previously diagnosed in human infection in Australia.

Cryptococcus neoformans var. gattii infection in northern Australia: existence of an environmental source other than known host eucalypts

The 2 known host trees of Cryptococcus neoformans var. gattii, Eucalyptus camaldulensis and E. tereticornis, do not occur naturally in the 'Top End' of the Northern Territory (NT) of Australia. Nine clinical isolates of C. neoformans var. gattii from the NT were analysed by random amplification of polymorphic deoxyribonucleic acid (RAPD) and polymerase chain reaction 'fingerprinting'. Two isolates were assigned to RAPD profile VGI, previously established as the common RAPD profile. The remaining 7 were assigned to profile VGII; 6 of these isolates were recovered from individuals living in the 'Top End'. The results strongly support the existence of an alternative environmental niche for C. neoformans var. gattii, as all isolates from Eucalyptus spp. in Australia to date have been of RAPD profile VGI.