Aleuriospores of Paracoccidioides brasiliensis

In soil extract agar and in Bennett medium abundant aleuriospores ofParacoccidioides brasiliensis have been observed. The possibility that these spores could be the infecting elements for man is discussed.

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Resumen Se han observado abundantes aleuriosporas deParacoccidioides brasiliensis en agar extracto de tierra y en medio de Bennett. Se discute la posibilidad de que éstas esporas puedan ser los elementos que infectan al hombre.

     

The pathobiology of Paracoccidioides brasiliensis

Paracoccidioides brasiliensis causes one of the most prevalent systemic mycoses in Latin America--paracoccidioidomycosis. It is a dimorphic fungus that undergoes a complex transformation in vivo, with mycelia in the environment producing conidia, which probably act as infectious propagules upon inhalation into the lungs, where they transform to the pathogenic yeast form. This transition is readily induced in vitro by temperature changes, resulting in modulation of the composition of the cell wall. Notably, the polymer linkages change from beta-glucan to alpha-glucan, possibly to avoid beta-glucan triggering the inflammatory response. Mammalian oestrogens inhibit this transition, giving rise to a higher incidence of disease in males. Furthermore, the susceptibility of individuals to paracoccidioidomycosis has a genetic basis, which results in a depressed cellular immune response in susceptible patients; resistance is conferred by cytokine-stimulated granuloma formation and nitric oxide production. The latency period and persistence of the disease and the apparent lack of efficacy of humoral immunity are consistent with P. brasiliensis existing as a facultative intracellular pathogen.     

Ornithine decarboxylase in Paracoccidioides brasiliensis

Ornithine decarboxylase in Paracoccidioides brasiliensis, a dimorphic human pathogenic fungus, was more active at 37° C in the yeast phase and at 30° C in the mycelial phase. In contrast to other fungal systems, yeast growth and mycelium-to-yeast transition in P. brasiliensis were accompanied by a high activity of ornithine decarboxylase at the onset of the budding process, the activity of which was inhibited by 1,4-diamino-2-butanone. The activity of ornithine decarboxylase remained at a basal level during vegetative growth of both the mycelial phase and the late stage of yeast phase, and also through the yeast-to-mycelium transition. Received: 18 December 1995 / Accepted: 8 March 1996     

Intrayeast hyphae in Paracoccidioides brasiliensis

The occurrence of a live hypha inside a dead yeast during the transformation from yeast to mycelium of Paracoccidioides brasiliensis is described.     

Characteristics of 17Paracoccidioides brasiliensis isolates

We have studied the physiological and morphological features of 17 isolates ofParacoccidioides brasiliensis in order to define their phenotypes. The isolates were cultured at room temperature on potato dextrose agar (PDA, Difco) slants for mycelial growth and in 1% dextrose brain heart infusion agar (BHIA, Difco) at 37°C for the study of yeast forms. Most mycelial and yeast forms grew well between pH 5.6–9.4. In their response to osmotic pressure the isolates were separated in three groups: intolerant, intermediate and tolerant. They also varied in carbohydrate assimilation tests, which indicated important metabolic variation. No clear differences were observed in phenol oxidase tests, KNO₃, starch, casein and arbutin assimilation tests. Only 1 of the isolates, Bt-19, had gelatinase activity. No correlation was observed between the above differences and virulence. Two patterns of growth were observed in the mycelial cultures, glabrous and cottonous, the latter being correlated with increased virulence for ddY mice. Most yeast forms grew as cerebriform colonies, but Pb-HC and Bt-19 colonies had a cobblestone-like surface.     

Cytosolic Neutral Proteinases of Paracoccidioides brasiliensis

Cytosolic proteinases were assayed in both morphological phases of Paracoccidioides brasiliensis. Preparations from the mycelial phase were more active in vitro than those from the yeast cells. Optimal proteinase activities for both phases occurred at pH's between 6.0 and 9.0, and at 45°C. Gelatin-SDS-PAGE electrophoresis separated several bands (58–112 kDa) in mycelial preparations; a single band (70 kDa) was seen in yeast preparations. Enzymatic activities were inhibited by antipain, phenyl methyl sulfonyl fluoride (PMSF), and chymostatin, suggestive of serine proteinases. Partial inhibition of the mycelial enzymes by ethylene diamine tetraacetic acid (EDTA), 1,10-phenanthroline, and iodoacetamide, also suggested the presence of cysteine- and metallo-proteinases. The enzymatic activity increased in preparations extracted from yeast cells transforming to mycelia, and decreased in preparations obtained from the reverse process. Received: 29 September 1997 / Accepted: 19 February 1998     

Morphogenesis of the mycelium-to-yeast transformation in Paracoccidioides brasiliensis

The sequential changes observed during the mycelium to yeast transformation in Paracoccidioides brasiliensis were studied microscopically. The mycelial elements produced terminal and intercalary swellings which, later on, became chlamydospore-like structures. These increased in size, acquired a double contour and, finally, gave rise to multiple budding cells. Transformation was asynchronous. During the observation period, multiple budding cells and chlamydospores remained attached to the parent mycelium.     

Innate immunity to Paracoccidioides brasiliensis infection

Innate immunity is based in pre-existing elements of the immune system that directly interact with all types of microbes leading to their destruction or growth inhibition. Several elements of this early defense mechanism act in concert to control initial pathogen growth and have profound effect on the adaptative immune response that further develops. Although most studies in paracoccidioidomycosis have been dedicated to understand cellular and humoral immune responses, innate immunity remains poorly defined. Hence, the main purpose of this review is to present and discuss some mechanisms of innate immunity developed by resistant and susceptible mice to Paracoccidioides brasiliensis infection, trying to understand how this initial host-pathogen interface interferes with the protective or deleterious adaptative immune response that will dictate disease outcome. An analysis of some mechanisms and mediators of innate immunity such as the activation of complement proteins, the microbicidal activity of natural killer cells and phagocytes, the production of inflammatory eicosanoids, cytokines, and chemokines among others, is presented trying to show the important role played by innate immunity in the host response to P. brasiliensis infection.