L23: Introduction to Mycology Flashcards
Ways in which fungi are agents of human disease?
- ) Mycotoxins: ergot alkaloids, aflatoxin, stachybotrys
2. ) Allergens
Fungi are eukaryotes – True / False
- True
Differences between fungal eukaryotic cells and human eukaryotic cells?
1.) Cell wall (not peptidoglycan): chitin (from NAG), chitosan, cellulose and alpha-glucan (from glucose) and mannan (from D-mannose)
2.) Cell membrane is composed of ergosterol, whereas this sterol is cholesterol in humans
• Cryptococcus neoformans possesses a capsule
Function of fungal cell wall
- ) Shape
- ) Rigidity
- ) Strength
- ) Protection from osmotic shock
Function of fungal cell membrane
- ) Contain cytoplasm
2. ) Regulate nutrient flow
Difference between fungal structures yeast and molds
1.) Yeast = unicellular, white
2.) Molds = fuzzy appearance with different colors
• some fungi can grow as both and are known as dimorphic
How do yeast reproduce?
- Budding
What are pseudohyphae and germ tubes?
- Pseudohyphae are false hyphae formed by some yeast
- Germ tubes are structures formed by almost always, Candida albicans, when cultured in serum
How do molds produce?
- Asexually: produce conidia (micro, macro, chlamydo/arthro where spore forms within a strand)
- Sexually: produce spores
• think of spores and conidia as similar – both aerosolized
What are hyphae and mycelium? Two types of mycelium?
- Hyphae are long filamentous outgrowths of fungi. As a cluster they are known as mycelium. These protrude into the air (aerial mycelium) or into the substrate (vegetative mycelium)
What are superficial mycoses? Examples of these infections?
- Infection of outermost layers of skin and hair
- Example: pityriasis versicolor, tinea nigra, black and white piedra
What are cutaneous mycoses? Examples of these infections?
- Infection which extends deep into epidermis as well as invasive hair and nail infections.
- Examples: dermatophyte infections such as ringworm, athlete’s foot and jock itch
What are subcutaneous mycoses? Agents that cause these infections?
- Infections involving the dermis, subcutaneous tissues, muscle and fascia
- Agents: sporotrichosis, chloroblastomycosis
What are systemic mycoses? Causative agents of infections?
- Infection that originate primarily in the lung but may spread to any organ in the body
- Agents: dimorphic fungi such as Histoplasmosis, Blastomycosis, Paracoccidioidomycosis, Coccidioidomycosis and yeast: Cryptococcus
What are opportunistic mycoses? Causative agents of infections?
- Infection associated primarily with immunosuppressed individuals.
- Agents: Candidiasis, Aspergillosis, Zygomycosis, Pneumocystis carinii pneumonia
Which arm of the immune system is essential for controlling and eliminating fungal infections? Which patient populations do we therefore become concerned for?
- Cell-mediated/adaptive immune system
- Concern for: immunosuppressed pt (d/t steroids and radiation), AIDS pts, pt with T-cell and neutrophil deficit
Targets of antifungal medication
- ) Cell wall synthesis (glucan and chitin synthesis)
- ) Cell membrane synthesis (inhibitors of ergosterol synthesis)*
- ) Direct membrane damage (binds to ergosterol and disrupts them)*
- ) Disruption of microtubules and inhibition of mitosis
- ) Nucleic acid synthesis
* most common
MOA of polyenes
- direct damage of fungal cell membrane by binding to ergosterol
MOA of azoles
- disrupts ergosterol biosynthesis
MOA of nucleoside analogues such as flucytosine
- inhibits DNA/RNA synthesis
MOA of grisans
- inhibits microtubular function in fungi
MOA of allylamines
- Inhibits ergosterol synthesis
MOA of thiocarbamates
- inhibits ergosterol synthesis
MOA of morpholines
- inhibits ergosterol biosynthesis
MOA of amphotericin B
- this is a polyene class of drug
- causes small pore formation in antifungal cell membrane by binding to ergosterol, cells are disrupted osmotically
MOA of echinocandins
- inhibit beta-glucan synthesis and therefore disrupting fungal cell walls, used primarily in treating Candida and Aspergillus which are typically resistant to other antifungals
How are fungi typically diagnosed/identified in laboratory?
- Direct visualization of fungal elements typically
Function of KOH prep
- KOH may be used to examine hair, nails, skin, fluids, exudates or biopsies for identification of fungi
- 15% KOH dissolves specimens greater rate than fungi d/t chitinous cell wall
Specialized stains to visualize fungal cell wall
- ) chlorazol black
2. ) calcofluor white
Do fungi stain via gram staining?
- Yes, all stain gram positive
Special stain for Cryptococcus neoformans
- India ink – this fungi has thick polysaccharide capsule
What organism is the germ tube test looking to identify?
- Likely candida albicans
