Cell wall modifications during conidial maturation of the human pathogenic fungus Pseudallescheria boydii.

Progress in extending the life expectancy of cystic fibrosis (CF) patients remains jeopardized by the increasing incidence of fungal respiratory infections. Pseudallescheria boydii (P. boydii), an emerging pathogen of humans, is a filamentous fungus frequently isolated from the respiratory secretions of CF patients. It is commonly believed that infection by this fungus occurs through inhalation of airborne conidia, but the mechanisms allowing the adherence of Pseudallescheria to the host epithelial cells and its escape from the host immune defenses remain largely unknown. Given that the cell wall orchestrates all these processes, we were interested in studying its dynamic changes in conidia as function of the age of cultures. We found that the surface hydrophobicity and electronegative charge of conidia increased with the age of culture. Melanin that can influence the cell surface properties, was extracted from conidia and estimated using UV-visible spectrophotometry. Cells were also directly examined and compared using electron paramagnetic resonance (EPR) that determines the production of free radicals. Consistent with the increased amount of melanin, the EPR signal intensity decreased suggesting polymerization of melanin. These results were confirmed by flow cytometry after studying the effect of melanin polymerization on the surface accessibility of mannose-containing glycoconjugates to fluorescent concanavalin A. In the absence of melanin, conidia showed a marked increase in fluorescence intensity as the age of culture increased. Using atomic force microscopy, we were unable to find rodlet-forming hydrophobins, molecules that can also affect conidial surface properties. In conclusion, the changes in surface properties and biochemical composition of the conidial wall with the age of culture highlight the process of conidial maturation. Mannose-containing glycoconjugates that are involved in immune recognition, are progressively masked by polymerization of melanin, an antioxidant that is commonly thought to allow fungal escape from the host immune defenses.

El complejo Pseudallescheria/Scedosporium y taxas afines en la rutina del laboratorio micológico clínico / The Pseudallescheria/Scedoporium complex and related taxa in the routine of clinic mycological laboratory

El complejo Pseudallescheria/Scedosporium y taxas relacionados, pertenecientes a un grupo de microhongos con conidios viscosos e integrantes del orden Microascales, se presentan en diversos ambientes comunes asociados a las actividades humanas, ya sea en el suelo como en aguas contaminadas. Actualmente se consideran entre los mayores grupos de hongos filamentosos oportunistas causante de infecciones cutáneas y profundas en el hombre y otros mamíferos. El objetivo principal de este trabajo, consiste en reunir los datos primarios morfofisiológicos más relevantes, útiles para el micólogo médico en el laboratorio, con el aporte adicional de algunos aspectos, biológicos, ecológicos, taxonómicos y moleculares complementarios descritos en la literatura moderna.

The Pseudallescheria/Scedosporium complex and their related taxa are a group of fungus that conidia are presents in viscous mass and belong to the order Microascales. They are in several common enviroment related to human activities either in soil as in contaminated water. Nowadays they are considerated one of the most opportunistic group of filamentous fungus that may cause superficial and deep skin mycoses infections in man and other mammalian. The aim of this work is to gather the primary relevant morphophysiological aspects, usefull to the medical mycologist in the laboratory, plus the contribution of some of biological, ecological, taxonomical and moleculars complementary aspects that are describe in modern literature.

Discrimination of Scedosporium prolificans against Pseudallescheria boydii and Scedosporium apiospermum by semiautomated repetitive sequence-based PCR.

The laboratory identification of Pseudallescheria and Scedosporium isolates at the species level is important for clinical and epidemiological purposes. This study used semiautomated repetitive sequence-based polymerase chain reaction (rep-PCR) to identify Pseudallescheria/Scedosporium. Reference strains of Pseudallescheria boydii (n = 12), Scedosporium prolificans (n = 8), Scedosporium apiospermum (n = 9), and clinical/environmental isolates (P. boydii, 7; S. prolificans, 7; S. apiospermum, 7) were analyzed by rep-PCR. All clinical isolates were identified by morphological and phenotypic characteristics and by sequence analysis. Species identification of reference strains was based on the results of available databases. Rep-PCR studies were also conducted with various molds to differentiate Pseudallescheria/Scedosporium spp. from other commonly encountered filamentous fungi. All tested Pseudallescheria/Scedosporium isolates were distinguishable from the other filamentous fungi. All Scedosporium prolificans strains clustered within the cutoff of 85%, and species identification by rep-PCR showed an agreement of 100% with sequence analysis. However, several isolates of P. boydii and S. apiospermum did not cluster within the 85% cutoff with the same species by rep-PCR. Although the identification of P. boydii and S. apiospermum was not correct, the semiautomated rep-PCR system is a promising tool for the identification of S. prolificans isolates.

Molecular and phenotypic data supporting distinct species statuses for Scedosporium apiospermum and Pseudallescheria boydii and the proposed new species Scedosporium dehoogii.

Based on the morphological, physiologic, and molecular (beta-tubulin gene) study of 141 isolates of the Pseudallescheria boydii species complex (including several synonyms) and relatives, the new species Scedosporium dehoogii is proposed. Scedosporium apiospermum and P. boydii are considered two different species and the new name Scedosporium boydii is proposed for the anamorph of the latter species. A summary of the key morphological and physiological features for distinguishing the species of Pseudallescheria/Scedosporium is provided.

Development of bioreactor system for treatment of dioxin-contaminated soil using Pseudallescheria boydii.

We developed a conceptual feasible design of bioreactor system for treatment of dioxin-contaminated soils that uses the dioxin-degrading fungus Pseudallescheria boydii (P. boydii) we had isolated. The dioxin-degradation conditions in bioreactor treatment was established by clarifying the inhibiting factors for the growth of P. boydii using both real contaminated and laboratory prepared soils mixed with fly ash. In addition, ethanol extraction process as post-treatment methods for the remaining dioxins, and the sterilization conditions of P. boydii, i.e., a weakly pathogenic fungus, in the residue was investigated. The better growth conditions of P. boydii were found to be chloride ion concentration of less than 10 g/L and a pH of less than 9. Under these conditions, 7310 pg-TEQ/g of the soil was treated to 2860 pg-TEQ/g by the bioreactor process, and the dioxin concentration was further decreased to 580 pg-TEQ/g by ethanol extraction, resulting to total removal ratio of 92%. Furthermore, development of an effective sterilization method for living P. boydii in the residue increased the applicability of our bioreactor system for practical use in dioxin-contaminated sites.

Pseudallescheriasis in the 21st century.

Since its discovery as an agent of mycetoma nearly a century ago, Pseudallescheria boydii with its asexual (synanamorphic) form, Scedosporium apiospermum, is now recognized as an important emerging opportunistic pathogen causing invasive mycosis in immunocompromised patients. The clinical spectrum of pseudallescheriasis is wide. Invasive disease of the lung, CNS and dissemination are serious manifestations in immunocompromised patients. This organism responds poorly to amphotericin B, and its histopathologic resemblance to aspergillosis often results in a delay in diagnosis. In vitro data, animal models and accumulating clinical experience support the use of voriconazole as a primary treatment for pseudallescheriasis. This paper reviews the microbiology, ecology, epidemiologic trends, clinical manifestations and current treatment options of pseudallescheriasis.

Scedosporium apiospermum (Pseudallescheria boydii) endocarditis.

Scedosporium apiospermum, the asexual state of Pseudallescheria boydii, is increasingly recognized as an opportunistic pathogen. We report a case of native valve endocarditis due to this organism that developed in an elderly patient following a prolonged hospitalization. Literature on endocarditis caused by S. apiospermum and P. boydii is reviewed.

Fungal meningitis.

Fungi provide many benefits to humans. However, some of these fungi have the ability to become human pathogens. All the major fungal pathogens can produce meningitis. From the common cryptococcal meningitis to the rare fungal meningitis caused by a dimorphic or filamentous fungus, medical issues are discussed in this review on a fungus-specific basis. Both primary (Cryptococcus, Blastomyces, Histoplasma, Coccidioides, and other dimorphic fungi) and secondary (Aspergillus, Candida, and a series of molds) fungal pathogens can produce life-threatening central nervous system infections. These infections require immediate and precise diagnosis and carefully selected management strategies to optimize outcomes. In this review, we examine the epidemiology, pathogenesis, clinical manifestations, and treatment for fungal meningitis in all the major fungal groups.

Ecology and physiology of the emerging opportunistic fungi Pseudallescheria boydii and Scedosporium prolificans.

Nutritionally physiological patterns of Pseudallescheria boydii (Microascaceae) and the related species Scedosporium prolificans were established. Differences between the two species were found in assimilation of sucrose, ribitol, xylitol and L-arabinitol. In contrast, no physiological distinction could be made between the three intraspecific variants of P. boydii which have been recognized on the basis of nDNA/DNA homology data and of morphological and clinical differences. Some potential virulence factors were studied in the fungi mentioned above and in some related anamorphs. All species were capable of anaerobic growth, but differed in their temperature relations.