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The yeasts range from 3µm to 5µm and are oval or spherical cells. '''Pseudohyphae''' are produced by some yeasts which are chains of irregular yeast cells. '''Dimorphic fungi''' change from the mycelial form into yeasts in certain conditions, e.g. 37°C, or when inside animal tissue. Yeasts reproduce mainly by budding of the oval, unicellular or round thallus. The daughter cells may remain attached to the parent yeast cells for several generations forming chains or colonies. To identify yeasts, the ability to assimilate sugar and nitrogen and the fermentation of various sugar compounds is studied.[[Category:Fungi]][[Category:Fungi]]
The yeasts range from 3µm to 5µm and are oval or spherical cells. '''Pseudohyphae''' are produced by some yeasts which are chains of irregular yeast cells. '''Dimorphic fungi''' change from the mycelial form into yeasts in certain conditions, e.g. 37°C, or when inside animal tissue. Yeasts reproduce mainly by budding of the oval, unicellular or round thallus. The daughter cells may remain attached to the parent yeast cells for several generations forming chains or colonies. To identify yeasts, the ability to assimilate sugar and nitrogen and the fermentation of various sugar compounds is studied.[[Category:Fungi]][[Category:Fungi]]
=Major pathogenic fungi=
'''Superficial''': These infections affect only the skin, hair, nails etc.
*Generally not dangerous
*Examples- ''Hortaea werneckii'', causing tinea nigra, and ''Piedraia hortae'', causing black piedra
'''Cutaneous''': including [[Dermatophytosis|'''dermatophytoses''']]
*Only affect superficial keratinized tissue- skin, hair and nails
*Again generally not dangerous
*Examples- ''Candida albicans'', causing candidiasis of the skin and nails and ''Microsporum'' species
[[Subcutaneous Mycoses|'''Subcutaneous''']]: Usually cause chronic localised infections of the skin and underlying dermis
*Normally reside in soil and vegetation, entering the skin through cuts and grazes
*Can occasionally affect the deep tissues, e.g. bones and muscles
*Examples- ''Sporothrix schenkii'', causing sporotrichosis, ''Madurella mycetomatis'' causing mycetoma
[[Systemic Mycoses|'''Systemic''']]: Also known as '''deep''', '''endemic''' or '''primary'''
*Usually serious
*Sometimes fatal
*Examples- ''Histoplasma capsulatum'' causing histoplasmosis, ''Blastomyces dermatitidis''causing blastomycosis
'''Opportunistic''': Ubiquitous fungi that affect only susceptible hosts; immunocompetent individuals are normally resistant
*Examples- ''Aspergillus fumigatus'', causing aspergilliosis, ''Cryptococcus neoformans'', causing cryptococcosis