I. Special characteristics of Fungi - - heterotrophs - primarily saprophytic - (mushrooms, rusts, smuts, molds, mildews, yeasts & "lichen components")
A. Components - Chitin - cell wall, ergosterol in cell membrane (target of anti-fungal drugs)
B. Dimorphic Biphasic life cycle-
1. molds- hyphae (septate & non-septate - old terminology)
a. reproductive hyphae (aerial)
b. vegetative hyphae
2. mycelium - fuzzy, fluffy intertwined hyphae
3. yeasts - single celled - budding, pseudohyphae
4. Medically important dimorphic fungi - Histoplasma capsulatum, Blastomyces dermatitidis, Coccidiodes immitis, Paracoccidioides braseilensis, Sporothrix schenkii, Pencillium marneffei. All are thermally dimorphic except cocci.
5. Thermally dimorphic - 25-30°C mold, 35-37°C yeast. Most fungi grow at 25C; human pathogens grow at 37C
C. Growth Optimums -Temperature, pH - Acid environments, Aerobic - except for yeasts; require 30 days incubation
D. Specialized media - BHI (primary), SABHI media (pathogenic fungi), dermatophyte test media DTM or Mycosel (dermatophytes contains chloramphenicol and cycloheximide), cornmeal w/Tween 80 agar (Candida), Nigel & Nitrate reduction (Crypto)
E. Special Culturing for fungi - cycloheximide used to reduce overgrowth by rapid fungi (probable contaminants), antibacterial agents to reduce contamination, CSF filtered and filter paper cultured, blood cultures 10-14 days, dermatophyte samples (skin and nails) do not refrigerate
F. Fungal Stains
| Stain | Fungi |
| AFB | Nocardia (branching bacterium) Blastomyces dermatitidis |
| Calcofluor white | mixed with KOH - all fungi |
| Gram Stain | GP |
| India Ink | Crytpococcus neoformans |
| PAS Periodic Acid-Schiff | stains all elements |
| lactophenol cotton blue (aniline blue) | wet mount |
G. Taxonomy 4 phyla based on Sexual and Asexual reproduction
| Phyla | Description of hyphae and reproductive spores | Medically Important Genera |
| Zygomycota | sparsely septate hyphae - asexual sporangiospores, sexual zygospores | Rhizopus, Mucor |
| Ascomycota | true sepatate hyphae - asexual - conidia, sexual conidiospores | Saccaromyces, (some) Candida - Ajellomyces form of Histoplasma, Blastomyces |
| Basidiomycota | sexual basidiospores | (plant pathogens, smuts, rusts, mushrooms), Cryptococcus |
| Deuteromycota | asexual conidia, no sexual reproduction | Alternaria, Aspergillus, Blastomyces, Candida, Coccidiodes, Epidermophyton, Fusarium, Geotrichum, Histoplasma, Microsporum, Paracoccidiodes, Penicillium, Sporothrix, Trichophyton |
H. Medical Classification
| Category | Definition | Medically Important Species |
| Superficial or cutaneous mycoses | involve hair, skin, nails (no deeper invasion) | dermatophytes -ringworm, athletes foot, tinea, piedra, candidiosis |
| Subcutaneous mycoses | confined to sub-cutaneous | chromoblastomycosis, sporotrichosis, mycetoma, phaeohyphomycosis |
| Systemic mycoses | systemic infections with organ invasion | aspergillosis, blastomycosis, candidiosis, coccidiomycosis, paracoccidiodes, Penicillium marneffei |
| Opportunistic mycoses | infections in immunosuppressed patients | aspergillosis, candidiosis, cryptococcosis, geotrichosis, zygomycosis, fusariosis |
II. Epidemiology of Fungal infections
A. Reservoir is Environmental
1. inhaled or contacted through broken skin
B. Endemic but not epidemic - most not communicable
C. Control of fungal infections - No vaccines
1. Filtration
2. animal contact
3. Fungicides in showers
4. Special precautions for Candida
5. Special care; Immunosuppressed
D. Skin Testing -as an epidemiologic tool
E. Diagnosis
1. Requires 4-6 weeks
2. based on hyphae (present, absent, septate [pigmented or not] condia morphology (see pages 712-715)
3. Urease test - differentiates Candida from Cryptococcus
4. Germ Tube production - C. albicans
III. Important Fungal Infections - most are endemic or associated with particular animal spread
| Disease | Etiologic Agent | Pathogenesis & Transmission & sites of infection |
Clinical form/Lab Tests |
|---|---|---|---|
| Valley Fever | Coccidiodes immitis | Arthrospores from soil, very small
spores 60%
asymptomatic, *not contagious; survive in dead organisms w/i soil |
spherules & endospores culture, serology, immunodiffusion |
| Cryptococcosis | Cryptococcus neoformans | Urban environments, associated
with pigeon droppings gelatinous capsule evades phagocytosis lungs->blood->brain |
yeast India ink direct smear of CSF |
| Ohio Valley Fever | Histoplasmosis capsulatum | Bat and Bird feces inhaled, lung, skin, eye |
yeast |
| Aspergilliosis | Aspergillus spp. | ubiquitous, found in patients on corticosteroids which target macrophages and T-cells | hyphae |
| Blastmomycosis | Blastomyces dermatitidis | soil as source? inhaled lungs, skin, bones |
yeast |
| Candidiosis CMCC (Chronic mucocutaneous Candidiasis) |
Candida spp. Candida albicans |
endogenus, direct invasion and
dissemination GI, GU, nails, organs, blood |
yeast, pseudohyphae |
| Paracoccidiomycoses | Paracoccidiodes brasiliensis | soil, plants
inhalation/trauma |
yeast |
| Sporotrichosis
|
Sporothrix schenkii | soil/plants
trauma, ulcerating wounds |
yeast |
| Dermatophytes: see page 749 microconidia small unicellular macroconidia - large multiseptate club or spindle shaped p 744 |
Epidermophyton- skin and nails
|
macroconidia (rounded) | hyphae |
| Microsporum- hair and skin | macroconidia (pointed) | hyphae | |
| Trichophyton-hair, skin, nails | no UV light; microconidia or no conidia | hyphae |
|
Eyes: Fusarium Alternaria |
Bone Marrow: Histoplasma Bone: Blastomyces |
CSF: Cryptococcus Coccidiodes immitis Histoplasma |
Respiratory: Penicillium Apergillus Rhizopus Geotrichum Alternaria Coccidiodes immitis |
VI. Aspergillus flavus - aflatoxin - most powerful carcinogen known to man (liver cancer)
1. peanuts, corn, etc.
B. Claviceps purpurea - ergotism - alkaloids - rye and other grains
C. Hallucinogenic Fungi
D. Amanita virosa - highly poisonous peptides amanitin and phalloidin
Link to Anti-fungal Chemotherapeutic Agents