Isolation and characterization of a new fungal genus and species, Aphanoascella galapagosensis, from carapace keratitis of a Galapagos tortoise (Chelonoidis nigra microphyes)

A new fungal genus and species, Aphanoascella galapagosensis, recovered from carapace keratitis in a Galapagos tortoise residing in a south Texas zoological collection, is characterized and described. The presence of a pale peridium composed of textura epidermoidea surrounded by scarce Hülle cell-like chlamydospores, and the characteristic reticulate ascospores with an equatorial rim separates it from other genera within the Onygenales. The phylogenetic tree inferred from the analysis of D1/D2 sequences demonstrates that this fungus represents a new lineage within that order. As D1/D2 and ITS sequence data also shows a further separation of Aphanoascus spp. into two monophyletic groups, we propose to retain the generic name Keratinophyton for species whose ascospores are pitted and display a conspicuous equatorial rim, and thereby propose new combinations in this genus for four Aphanoascus species.

In utero infection of a calf by Saksenaea erythrospora resulting in neonatal abomasitis and dermatitis

Saksenaea erythrospora is a filamentous fungus belonging to the order Mucorales. Cases of cutaneous mucormycosis caused by Saksenaea spp. have previously been reported in immunocompetent and immunosuppressed people. A premature, 1-day-old bull calf from Texas with numerous plaque-like and ulcerative lesions in the skin was found at necropsy to have multiple areas of mycotic dermatitis and abomasitis. Fungal culture of the skin followed by morphological characterization and genetic analysis identified the etiologic agent as S. erythrospora.

Invasive Mycoleptodiscus fungal cellulitis and myositis

We report progressive necrotizing fungal cellulitis and myositis in the leg of a patient with glioblastoma multiforme treated with temozolomide and corticosteroids. While the morphologic appearance of the isolate and its ability to grow at temperatures greater than 32°C were suggestive of Mycoleptodiscus indicus, some of the conidia were atypical for this species in that they had single septa and occasional lateral appendages. Furthermore, the isolate was different from M. indicus based on the sequencing analysis of two rDNA regions. This is the first case of Mycoleptodiscus invasive fungal disease in which the causative agent could not be resolved at the species level because of inconsistencies between morphological and molecular data.

Insertional mutagenesis combined with an inducible filamentation phenotype reveals a conserved STE50 homologue in Cryptococcus neoformans that is required for monokaryotic fruiting and sexual reproduction

Cryptococcus neoformans typically grows in a yeast-like morphology; however, under specific conditions the fungus can produce hyphae that are either dikaryotic or monokaryotic. In this study, we developed a simple method for inducing robust monokaryotic fruiting and combined the assay with Agrobacterium tumefaciens insertional mutagenesis to screen for hyphal mutants. A C. neoformans homologue of the Saccharomyces cerevisiae STE50 gene was identified and characterized. STE50 was found to be required for sexual reproduction and monokaryotic fruiting. Ste50p has conserved SAM and RA domains, as well as two SH3 domains specific to basidiomycetous Ste50 proteins. Analysis of protein-protein interaction showed that Ste50p can interact with Ste11p and Ste20p, and epistasis experiments placed STE50 between STE20 and STE11. Genetic analysis of the role of STE50 in sexual reproduction showed that it was required for all steps, from response to pheromone to production of hyphae. Analysis of the effect of individual Ste50p domains on sexual reproduction and monokaryotic fruiting revealed domain-specific effects for both processes. This study revealed that the C. neoformans STE50 gene has both conserved and novel functions during sexual reproduction and monokaryotic fruiting, and these functions are domain-dependent.

Geosmithia argillacea: an emerging cause of invasive mycosis in human chronic granulomatous disease

BACKGROUND

Chronic granulomatous disease (CGD) is an inherited disorder of the nicotinamide adenine dinucleotide phosphate oxidase that leads to defective production of microbicidal superoxide and other oxidative radicals, resulting in increased susceptibility to invasive infections, especially those due to fungi.

METHODS

Geosmithia argillacea was identified from cultured isolates by genomic sequencing of the internal transcribed spacer region. Isolates previously identified as Paecilomyces variotii, a filamentous fungus closely resembling G. argillacea, were also examined.

RESULTS

We identified G. argillacea as the cause of invasive mycosis in 7 CGD patients. In 5 cases, the fungus had been previously identified morphologically as P. variotii. All patients had pulmonary lesions; 1 had disseminated lesions following inhalational pneumonia. Infections involved the chest wall and contiguous ribs in 2 patients and disseminated to the brain in 1 patient. Four patients with pneumonia underwent surgical intervention. All patients responded poorly to medical treatment, and 3 died.

CONCLUSIONS

We report the first cases of invasive mycosis caused by G. argillacea in CGD patients. G. argillacea infections in CGD are often refractory and severe with a high fatality rate. Surgical intervention has been effective in some cases. G. argillacea is a previously underappreciated and frequently misidentified pathogen in CGD that should be excluded when P. variotii is identified morphologically.

A case of bovine valve endocarditis caused by Engyodontium album

We report the first case of Engyodontium album bioprosthetic valve endocarditis in a 44-year-old male with a history of juvenile rheumatoid arthritis. There is only one other report of Engyodontium album as a human pathogen. The present case supports the increased incidence of fungal endocarditis especially in patients receiving immunotherapy.

Disseminated Oxyporus corticola infection in a German shepherd dog

The filamentous basidiomycetous fungus, Oxyporus corticola, has not previously been reported in the human or veterinary medical literature. Identification of this organism as the etiologic agent of fungal osteomyelitis and multiorgan dissemination in a German shepherd dog was confirmed by comparison of ITS and D1/D2 sequences with known isolates.

Disseminated Geosmithia argillacea infection in a German shepherd dog

We report a systemic mycosis in a German Shepherd dog caused by Geosmithia argillacea. Although this etiologic agent microscopically resembles a Penicillium species, and is histopathologically compatible with members of the genus Aspergillus, morphologic features and molecular characterization clearly separate it from these genera. This appears to be the first report of disseminated disease by this species in humans or animals. In vitro antifungal susceptibility testing suggests resistance to amphotericin B and voriconazole and susceptibility to caspofungin, itraconazole, and posaconazole.

Pulmonary Phialemonium curvatum phaeohyphomycosis in a Standard Poodle dog

Phialemonium curvatum, frequently misidentified as an Acremonium species, is reported here as a new agent of pulmonary phaeohyphomycosis in a Standard Poodle dog, and added as a new species in the genus to cause mycoses in canines. In vitro susceptibility data, for both human and animal isolates, suggests resistance to amphotericin B and susceptibility to the triazole agents itraconazole, voriconazole, and posaconazole.

A seed and feed model for the formation of Candida albicans biofilms under flow conditions using an improved modified Robbins device

A variety of manifestations of Candida albicans infections are associated with the formation of biofilms on the surface of biomaterials. In order to maintain their niche these adherent populations need to withstand the continuous bathing action of physiological fluids (saliva, blood), which also provide water and nutrients to the fungal cells. Thus, it was the aim of this study to examine and further characterize the development of C. albicans biofilms under shear forces and a flow of replenishing nutrients, emulating the conditions that fungal cells would normally encounter within the host. An improved modified Robbins device (MRD) was designed to hold six poly methyl methacrylate (PMMA) plugs of 25 mm in diameter. A "seed and feed" model of biofilm formation was then implemented for which the apparatus was initially seeded with a C. albicans cell suspension to allow initial adhesion of fungal cells to the biomaterial. Following this initial step, sterile medium was then pumped through the MRD at a constant flow rate. Scanning electron microscopy (SEM) and confocal scanning laser microscopy (CSLM) demonstrated a high degree of heterogeneity associated with the structure of biofilms formed under flowing conditions using the MRD. In addition, these biofilms displayed a complex three dimensional architecture and increased production of exopolymeric material.

Inhibition on Candida albicans biofilm formation using divalent cation chelators (EDTA)

Candida albicans can readily form biofilms on both inanimate and biological surfaces. In this study we investigated a means of inhibiting biofilm formation using EDTA (Ethylenediaminetetra-acetic acid), a divalent cation chelating agent, which has been shown to affect C. albicans filamentation. Candida albicans biofilms were formed in 96-well microtitre plates. Cells were allowed to adhere for 1, 2, and 4 h at 37 degrees C, washed in PBS, and then treated with different concentrations of EDTA (0, 2.5, 25, and 250 mM). EDTA was also added to the standardized suspension prior to adding to the microtiter plate and to a preformed 24 h biofilm. All plates were then incubated at 37 degrees C for an additional 24 h to allow for biofilm formation. The extent and characteristics of biofilm formation were then microscopically assessed and with a semi-quantitative colorimetric technique based on the use of an XTT-reduction assay. Northern blot analysis of the hyphal wall protein (HWP1) expression was also monitored in planktonic and biofilm cells treated with EDTA. Microscopic analysis and colorimetric readings revealed that filamentation and biofilm formation were inhibited by EDTA in a concentration dependent manner. However, preformed biofilms were minimally affected by EDTA (maximum of 31% reduction at 250 mM). The HWP1 gene expression was reduced in EDTA-treated planktonic and biofilm samples. These results indicate that EDTA inhibits C. albicans biofilm formation are most likely through its inhibitory effect on filamentation and indicates the potential therapeutic effects of EDTA. This compound may serve a non-toxic means of preventing biofilm formation on infections with a C. albicans biofilm etiology.

A retrotransposon-derived probe for discriminating strains of Cryptococcus neoformans

Hybridization of digested DNA to probes derived from repeated sequences has proven to be an extremely powerful epidemiologic tool for studying the relatedness of fungi. The dispersed nature of these sequences throughout the genome provides the discriminatory power for distinguishing two independent isolates from each other based on banding pattern. The genome of Cryptococcus neoformans contains a number of classes of transposable elements, which are often present in multiple copies. We characterized a probe related to the Ty3/gypsy class of transposable elements called TCN1 and used it to screen multiple isolates from all four serotypes of C. neoformans. DNA with TCN1 homology could be amplified from each isolate of serotypes A and D and all isolates hybridized to a probe derived from TCN1. Isolates from serotype B and C were also tested for the presence of a TCN1 homolog, however, only some of these isolates yielded both a TCN1-specific PCR product or hybridization signal. Comparison of the TCN1 hybridization patterns of serotypes A and D to multiple RAPD patterns of the same isolates suggested that TCN1 was more discriminating and therefore, a useful epidemiological tool.

Lecythophora mutabilisprosthetic valve endocarditis in a diabetic patient

While dematiaceous (dark-walled) fungi are ubiquitous in the environment, their involvement in invasive human infections has rarely been reported. However, these organisms have been identified as potential emerging pathogens, particularly among immunocompromised hosts. We describe a diabetic patient with Lecythophora mutabilis prosthetic valve endocarditis who was treated surgically, as well as with amphotericin B lipid complex and voriconazole, which were subsequently followed by prolonged voriconazole suppressive therapy. To the best of our knowledge, our patient is the first reported survivor of L. mutabilis prosthetic valve endocarditis.

Genotyping of Turkish environmental Cryptococcus neoformans var. neoformans isolates by pulsed field gel electrophoresis and mating type

A total of 26 environmental Cryptococcus neoformans var. neoformans strains isolated from 634 samples of pigeon droppings collected from 54 different provinces of Turkey in 1996 and 1997 were included in this study. The results of pulsed-field gel electrophoresis (PFGE) showed that the 26 strains could be separated into 24 different PFGE patterns. In a mating-type study, of 26 strains, 20 were MATalpha, four were MATa, one was MATa/alpha and one was non-typable by STE20 specific primers. By the polymerase chain reaction typing, all the isolates were serotype A. The extensive heterogeneity among these isolates suggests that a single clonal population may not be present in Turkey. Additionally, the presence of an AMATa/DMATalpha hybrid may indicate the existence of strains that are AMATa mating type in Turkish environment.

Split marker transformation increases homologous integration frequency in Cryptococcus neoformans

Gene disruption in Cryptococcus neoformans can be problematic due to high frequencies of ectopic integration and telomerization. To improve the frequency of homologous integration, a transformation strategy was employed called split marker, which utilizes a mixture of DNAs comprised of overlapping truncations of the selectable marker. Five genes were compared for homologous integration frequencies using various constructs. Homologous integration was highest when the split marker approach was used, with rates as high as 60% depending on target gene. A second factor that contributed to an increased homologous integration frequency was strain background, which was highest when a double auxotroph was used as a host. The split marker strategy was combined with an ura-blaster construct, which has been used in other fungi to recycle ura5 or ura3 mutations. When a hisG-URA5-hisG cassette was successfully integrated at the target locus, the URA5 gene could be easily evicted by plating onto 5-FOA agar. The cassette was then successfully used for a second cycle of transformation-eviction. The effectiveness of the split marker disruption strategy suggests that continued investigation and modification of traditional molecular techniques could increase the efficiency of C. neoformans molecular manipulation.

Relationship between metabolism and biomass of medically important zygomycetes

Little is known about the relationships between metabolic activity and fungal biomass or time of incubation for medically important fungal pathogens. Understanding these relationships may be especially relevant for rapidly growing organisms, such as zygomycetes. A range of inocula of five clinical isolates of zygomycetes (one each of Rhizopus oryzae,Rhizopus microsporus, Cunninghamella bertholletiae, Mucor circinelloides and Absidia corymbifera) were incubated for 6, 8, 12, 24 and 48 h, after which hyphal mass was assessed spectrophotometrically and metabolic activity was measured using various concentrations of XTT and menadione. Both linear regression and the Boltzmann sigmoid model were used and compared for description of relationships between metabolic activity, biomass and time of incubation. Modeling was further applied to eleven additional zygomycete isolates. The relationships of biomass or metabolic activity as a function of time of incubation were well described with the Boltzmann sigmoid model. The latter was superior to linear regression in describing the relationship between metabolic activity and fungal biomass. For all isolates of zygomycetes, increases in metabolic activity preceded increases in biomass. Inter-species differences in growth patterns were observed, with Rhizopus microsporus and Mucor spp. reaching the plateau of growth earlier compared to other species. These findings on the temporal relationship and inter-species differences of hyphal growth and metabolic activity for zygomycetes may be useful in the design and interpretation of in vitro studies of these emerging pathogens.

Molecular epidemiology of clinical Cryptococcus neoformans strains from India

Little is known about the molecular epidemiology of the human pathogenic fungus Cryptococcus neoformans in India, a country now in the midst of an epidemic of AIDS-related cryptococcosis. We studied 57 clinical isolates from several regions in India, of which 51 were C. neoformans var. grubii, 1 was C. neoformans var. neoformans, and 5 were C. neoformans var. gattii. This strain set included 18 additional sequential isolates from 14 patients. Strains were characterized phenotypically by measuring the polysaccharide capsule and by determining the MICs of standard antifungals. Molecular typing was performed by a PCR-based method using the minisatellite-specific core sequence (M13), by electrophoretic karyotyping, by restriction fragment length polymorphisms with the C. neoformans transposon 1 (TCN-1), and by URA5 DNA sequence analysis. Overall, Indian isolates were less heterogeneous than isolates from other regions and included a subset that clustered into one group based on URA5 DNA sequence analysis. In summary, our results demonstrate (i) differences in genetic diversity of C. neoformans isolates from India compared to isolates from other regions in the world; (ii) that DNA typing with the TCN-1 probe can adequately distinguish C. neoformans var. grubii strains; (iii) that TCN-1 sequences are absent in many C. neoformans var. gattii strains, supporting previous studies indicating that these strains have a limited geographical dispersal; and (iv) that human cryptococcal infection can be associated with microevolution of the infecting strain and by simultaneous coinfection with two distinct C. neoformans strains.

Comparative analysis of pathogenicity of Cryptococcus neoformans serotypes A, D and AD in murine cryptococcosis

OBJECTIVES

To characterize the pathogenicity of 15 strains of Cryptococcus neoformans belonging to several serotype/mating type allele patterns (Dalpha, Da, A(alpha), A(a), A(alpha)/D(a) and D(alpha)/A(a)) in experimental models of murine cryptococcosis.

METHODS

CD1-infected mice were examined for survival and fungal loads in either brain or lung during the course of infection.

RESULTS

All strains, with the exception of one Da strain, produced melanin in vitro. Similarly, all strains were encapsulated and produced phospholipase. When CD1 mice were challenged intravenously (i.v.) with 5x10(5)CFU/mouse and observed for 60 days post-infection, a significant variation of mortality rate was observed among mice infected with different strains. A(alpha) and A(alpha)/D(a) strains all produced 100% mortality within the study period with mean survivals significantly shorter than those of mice infected with strains belonging to any other allele type (P<0.0001). A wide range of pathogenicity was shown by haploid and diploid strains presenting D(alpha) allele. This finding was confirmed by an intranasal model of challenge. To investigate the progression of infection, the mice were challenged i.v. with 5x10(4)CFU/mouse and tissue burden experiments (brain and lung) were performed on days 6 and 12 post-infection. Only the mice infected with A(alpha) and A(alpha)/D(a) strains showed a >1 log(10) increase of CFU/g in both tissues throughout the study period.

CONCLUSIONS

Our results suggest that the presence of the A(alpha) mating type allele in either haploid or diploid strains is correlated with virulence, while the presence of the A(a) or D(a) allele in haploid strains is associated with moderate or no virulence. Finally, either haploid or diploid strains presenting D(alpha) allele vary in virulence.

The genome of the basidiomycetous yeast and human pathogen Cryptococcus neoformans

Cryptococcus neoformans is a basidiomycetous yeast ubiquitous in the environment, a model for fungal pathogenesis, and an opportunistic human pathogen of global importance. We have sequenced its approximately 20-megabase genome, which contains approximately 6500 intron-rich gene structures and encodes a transcriptome abundant in alternatively spliced and antisense messages. The genome is rich in transposons, many of which cluster at candidate centromeric regions. The presence of these transposons may drive karyotype instability and phenotypic variation. C. neoformans encodes unique genes that may contribute to its unusual virulence properties, and comparison of two phenotypically distinct strains reveals variation in gene content in addition to sequence polymorphisms between the genomes.

Simple chemical extraction method for DNA isolation from Aspergillus fumigatus and other Aspergillus species

DNA was successfully isolated from numerous Aspergillus spp. by use of a commercial kit. DNA that was easily digested and yielded PCR products up to 8.5 kb in size was recovered from broth or agar cultures. The ease and speed of this protocol provide an alternative to physical methods of DNA isolation.

Cloning and characterization of the lanosterol 14alpha-demethylase (ERG11) gene in Cryptococcus neoformans

The ergosterol pathway in fungal pathogens is an attractive antimicrobial target because it is unique from the major sterol (cholesterol) producing pathway in humans. Lanosterol 14alpha-demethylase is the target for a major class of antifungals, the azoles. In this study we have isolated the gene for this enzyme from Cryptococcus neoformans. The gene, ERG11, was recovered using degenerate PCR with primers designed with a novel algorithm called CODEHOP. Sequence analysis of Erg11p identified a highly conserved region typical of the cytochrome P450 class of mono-oxygenases. The gene was present in single copy in the genome and mapped to one end of the largest chromosome. Comparison of the protein sequence to a number of major human fungal pathogen Erg11p homologs revealed that the C. neoformans protein was highly conserved, and most closely related to the Erg11p homologs from other basidiomycetes. Functional studies demonstrated that the gene could complement a Saccharomyces cerevisiae erg11 mutant, which confirmed the identity of the C. neoformans gene.

Antifungal combinations against Candida albicans biofilms in vitro

Candida biofilms display increased resistance to most antifungal agents. We have evaluated the efficacy of combinations of fluconazole (FLC), amphotericin B, and caspofungin (CSP) against Candida albicans biofilms in vitro. Indifference was observed for all the combinations of paired antifungal agents when a checkerboard titration method was used. Time-kill experiments revealed an antagonistic effect of high FLC doses with CSP.