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Infectious Disease Online Cutaneous Infections and Infestations: Mycoses and Algal Infections
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Fungi are an important cause of dermatological disease. Visit: Cutaneous Infections and Infestations Fungal identification: The PAS stain (Periodic Acid-Schiff) , sometimes combined with diastase digestion, is most frequestly used. It stains the cell walls of fungi a purple colour of varying intensity. The silver methenamine stain, usually Grocott’s modification, is a reliable method of detecting fungi: It stains them black against a green background. It is more reliable than the PAS (Periodic Acid-Schiff) stain for detecting degenerate fungal elements and the rare animal pathogens among the aquatic fungi, although it may be less reliable with zygomycetes. Cryptococcus neoformans may be stained with the mucicarmine stain or a combined alcian blue-PAS (Periodic Acid-Schiff) stain, which shows the cell wall and capsule in contrasting colors. It is usually doubly refractile under polarized light. Calcoflour white can be used to stain frozen or paraffin sections as well as tissue smears. The sections must be viewed with a fluorescence microscope. Certain fungi are even autoflourescent when a section stained with hematoxylin and eosin is exposed to ultraviolet light. These include Blastomyces , Cryptococcus , Candida , Aspergillus , Coccidioides and occasionally Histoplasma. Polymerase chain reaction (PCR)-based techniques are now being used to identify specific species of fungi, including dermatophytes. Superficial filamentous infections: Yeast infections: Pityriasis versicolor Pityrosporum folliculitis Trichosporonosis and white piedra Systemic mycoses: Infection by dematiaceous fungi: Tinea nigra Mycetoma and morphologically similar conditions:
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