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Lab-5-
Fungi in Tissue
Fungi in Tissue (con’t.)
1.) Yeasts: These vary in size, shape, method of
dividing, with of without a capsule, etc.
The following illustrates several distinguishing
features of yeasts and the diseases they cause:
a.) Only one pathogenic yeast has a capsule. The disease it
causes is called Cryptococcosis:
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Fatal disease of brain (CSF), causing meningitis
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encapsulated yeast seen in India ink
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fluconazole and itraconazole
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5 cases/million normal population but >20% AIDS
PAS stain showing encapsulated
yeast in tissue
Pulmonary cryptococcosis
C. neoformans culture grown
at either 24 C or 35 C.
Organism is monomorphic.
C. neoformans as seen in
culture or in CSF. Note huge
capsule.
b.) Two mycoses have intracellular yeast. One of these is
Histoplasmosis and the other is Penicilliosis.
Histoplasmosis
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Granulomatous disease of lungs and RES which
mimics TB.
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Spread from bird droppings, especially blackbirds,
chickens and bats.
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Worldwide
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Hard to diagnose, use itraconazole.
Small (3-5 microns)
intracellular yeast of
H. capsulatum
Blood smear showing
three intracellular yeast of
H. capsulatum
Infectious form of
Histoplasma capsulatum
showing spores. In nature
or lab at 24 C.
Yeast (pathogenic) form as in
vivo or cultured at 35 C.
This is a dimorphic fungus.
The second intracellular yeast causes Penicilliosis. This is
a relatively new disease that is found exclusively in S.
China and S.E. Asia. It is the number 3 cause of death
for AIDS patients in Thailand.
Note characteristic “target” lesions of penicilliosis.
Dimorphic Penicillium marneffei
Note the numerous
intracellular yeast.
The infectious form of
Penicillium marneffei as
seen in nature or 24 C lab.
Sporotrichosis is caused by another dimorphic yeast called
“gardener’s disease”, acquired from plants .
Characteristic lymphadenopathy. Patient on right has
secondary bacterial infection.
Dimorphic cultures of Sporothrix schenckii
Infectious form cultured at 24 C.
Pathogenic (yeast) cultured at 35 C
Fungi in Tissue (con’t.)
2.) Sporangia. These are large (20-40 microns), round
elements which contains numerous spores. They cause
coccidioidomycosis which is endemic to SW United
States and Mexico. It is a fatal lung disease found
mostly in Asians and dark-skinned people.
Skin lesions in coccidioidomycosis.
The organism Coccidioides immitis is found in desert soils as
shown here. The spores become airborne, enter the lungs and
change into endospores.
Dimorphic forms of Coccidioides immitis
PAS stain showing
sporangia in lung tissue.
Highly infectious spores
growing in soil or in the
laboratory.