Paracoccidioides Mold SpeciesParacoccidioides brasiliensis is a causative agent of Paracoccidioidomycosis. (Information from www.doctorfungus.org @ 2005)
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Taxonomic Classifications
Kingdom:
Fungi
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Ecology The natural habitat of Paracoccidioides remains unknown, although it has been isolated only on a few occasions from non – medical sources, primarily from humid soil rich in proteins and from the digestive tract of some animals. It has been cultivated from fruit bats and armadillos. Paracoccidioides is a thermally dimorphic fungus. Its geographic distribution is restricted to South America where the majority of cases have been reported, particularly from Brazil, Venezuela, and Colombia. Recently, through random amplified polymorphic DNA analysis, the geographic discrimination of the strains has been made possible.
Species The genus Paracoccidioides contains only one species, Paracoccidioides brasiliensis. Paracoccidioides brasiliensis is an anamorphic fungus and has no known teleomorph.
Pathogenicity and Health Effects Paracoccidioides brasiliensis is the etiologic agent of a true systemic mycosis called paracoccidioidomycosis. The range of infection of this chronic illness is wide, varying from an asymptomatic infection or progression in the form of a pulmonary or disseminated infection which is characterized by formation of secondary lesions of the buccal, nasal or gastrointestinal mucosa and may also be infected are the lymph nodes and aortitis may develop. Diagnosis of paracoccidioidomycosis is often complicated. The infection may become evident several years after exposure to Paracoccidioides brasiliensis thus, suggesting the likelihood of a long latent period. This chronic illness is acquired via inhalation of the conidia, followed by primary infection of the lungs. The extent of pathogenicity may differ and appears strain – dependent. The fungal exocellular enzyme called serine – thiol proteinase is a significant virulence factor for tissue invasion. Acute pulmonary and disseminated paracoccidioidomycosis may rarely develop in immunocompromised patient. Given the true systemic nature of paracoccidioidomycosis, otherwise healthy individuals are affected.
Macroscopic Appearance Ø Paracoccidioides brasiliensis grows in mold form at 25°C and in its yeast form at 37°C due to its characteristic of being a thermally dimorphic fungus; Ø At 25°C, the colonies are glabrous and velvety, slow – growing, with diameter ranging from 1 – 2 cm within two to three weeks, the surface color is white, tan or brown while the reverse is yellowish brown to brown; Ø At 37°C, the colonies are yeast – like with creamy texture, white in color, heaped, wrinkled or folded; and Ø Enriched medium such as brain heart infusion agar supports mold to yeast conversion within ten to twenty days of incubation.
Microscopic Appearance Ø At 25°C, formation of hyaline septate hyphae which are sterile and do not sporulate and the conidia produced are oval – shaped, unicellular, truncate, with a broad base and rounded tip, and are found along the hyphae; and Ø At 37°C, formation of daughter cells which are attached to the mother cell by narrow neck portion which resembles a steering wheel and secondary cells in short chains are formed before the detachment of the original daughter cells from the mother cell.
Laboratory Precautions Isolates of Paracoccidioides brasiliensis must be handled with caution in a biological safety cabinet, even though, most strains are sterile and do not sporulate.
Susceptibility There are limited in vitro data on susceptibility activity of Paracoccidioides brasiliensis. Reference method is not standardized as yet and the methods that have been employed for susceptibility analysis also vary thus, meaningful comparisons are difficult to obtain. Generally, amphotericin B, ketoconazole, itraconazole, fluconazole, and voriconazole relatively yielded low MICs against the yeast phase of Paracoccidioides brasiliensis. However, higher itraconazole and fluconazole values have been reported for some isolates in another study. Additionally, cilofungin provided high MICs. Itraconazole now emerges as the drug of choice for treatment of paracoccidioidomycosis aside from amphotericin B, sulphonamides, and ketoconazole.
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