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FUNGAL ORGANISMS OF
MEDICAL IMPORTANCE
Fungi
Kingdom Fungi:
Eukaryotes
Fungi lack chorophyll
Fungal cell walls contain a carbohydrate called chitin
Fungal cell membranes contain ergosterol
Fungi are heterotrophic
Two phases of life cycle
Growth (vegetative) phase
Reproductive phase
Fungi
Groups
Molds: long, tangled filaments of cells that
give rise to visible colonies
Yeasts: unicellular organisms whose colonies
resemble those of bacteria
Dimorphic: grow as filamentous molds at 25C
but convert to unicellular pathogenic yeast
forms at 37C
Fungi
Culture medium for isolation: Sabouraud agar
Hyphae
Masses of intertwined filaments
Morphological unit of a filamentous fungus
Visible only with the aid of a microscope
Fungal Structure
Mycelium
Thick mass of
hyphae
Large enough to be
seen with the naked
eye
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Fungal Structure
Septa: hyphal cross walls
Septate
Nonseptate
Fungal diseases of
the skin
Cutaneous Mycosis
Dermatomycosis
Caused by dermatophytes
Fungi that colonize the hair, nails, and the
outer layer (stratum corneum) of the
epidermis
Grow on keratin in these areas causing tinea
(ringworms)
Moisture in these areas favor fungal infections
Dermatomycosis
Tinea capitis: ringworm of the scalp
Tinea cruris: ringworm of the groin (jock itch)
Tinea corporis: ringworm of the body
Tinea pedis: ringworm of the feet
Tinea unguium: nail ringworm
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Dermatomycosis
Three genera of fungi involved in cutaneous
mycosis
Trichophyton: infects hair, skin or nails
Microsporum: involves only the hair or skin
Epidermophyton: affects only the skin and nails
Diagnosis: KOH, Wood lamp
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Malassezia furfur
Causes pityriasis versicolor
Oval or irregular spots with occasional scaling
in back, underarm, upper arm, chest and neck
Hyperpigmented or hypopigmented
Yeast feeds on skin oils (lipids) as well as dead
skin cells
Spaghetti and meatball appearance of the
yeast
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Subcutaneous Mycosis
More serious than cutaneous mycosis
Penetrate the skin through small wound that allows
entry into subcutaneous tissues
Most common disease: sporotrichosis
Caused by Sporothrix schenkii
Occurs among gardeners or others working with soil
Infection frequently forms a small ulcer on the hands
Madura Foot
Chronic, granulomatous, fungal disease
Mainly affects the foot
Abscess discharges pus, serum, and blood
through sinuses
Most pathogenic agents: Madurella grisea and
Exophiala jeanselmei
Presence of colored grains, composed of
compacted hyphae, in the exudate
Treatment is surgical excision
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Fungi causing
systemic infections
Histoplasma capsulatum
Thermal dimorphic fungus
Transmission is by inhalation of airborne asexual
spores (microconidia)
Microconidia enter the lungs and differentiate
into yeast cells
Yeast cells are ingested by macrophages and
multiply within them
Most prevalent in central North America,
especially the Ohio and Mississippi River Valleys
Tongue
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Coccidioides immitis
Disease: Coccidioidomycosis
Thermally dimorphic fungus
Transmission is by inhalation of airborne
arthrospores
Develops in the lungs and disseminate within the
body
Occur in southwestern United States and Central and
South America (Valley fever)
Lung
Spleen
Blastomyces dermatitidis
Thermally dimorphic fungus
Produces microconidia, most often in the soil,
which become airborne and enter the lungs
Manifest as ulcerated granulomas in the
urogenital tract
Most common in the South Central and South
Eastern United States
More common in adult males than in females or
children
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Paracoccidioides brasiliensis
Thermally dimorphic fungus
Transmission: inhalation of airborne conidia
Inhaled conidia differentiate in the lungs and
disseminate to many organs
Restricted to Central and South America
>90 percent of patients males
Estrogen may inhibit formation of the yeast form
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Fungi causing opportunistic
infections
Aspergillus fumigatus
Disease: invasive aspergillosis; allergic
bronchopulmonary aspergillosis
Transmission: inhalation of airborne
conidia
Organism invades blood vessels causing
thrombosis and infarction
Fungus ball or aspergilloma develops in
the lung
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Candida albicans
Diseases: thrush, disseminated candidiasis, chronic
mucocutaneous candidiasis
Part of the normal flora of the skin, mucous
membranes, vagina and GI tract
Microscopic examination reveals yeasts and
pseudohyphae
Germ tube formation: characteristic of C. albicans
Not present in other Candida species
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Cryptococcus neoformans
Disease: Cryptococcosis (especially
cryptococcal meningitis)
Habitat is soil (enriched by pigeon droppings)
Transmission: inhalation of airborne yeast
cells
Cause influenza-like syndrome or pneumonia
Spread via bloodstream to the meninges
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Pneumocystis jiroveci
Formerly, P. carinii
Still often referred to as PCP, for P. carinii
pneumonia
Ergosterol, which is an essential component of
most fungal membranes, is lacking
One of the most common opportunistic
diseases of individuals infected with HIV-1
