Exam #1: Clinical Mycology Flashcards
How many species of fungi infect humans?
150 of 200,000
How can fungi cause disease?
- Intoxication i.e. through the production of microtoxins
○ Ergot alkaloids (bread fungi w/ ingestion leads to hallucinations)
○ Alfatoxin (peanut butter fungi that is hepatotoxic)
○ Stachybotrys (black mold in homes that produces neurotoxin)
○ Recreational “shrooms” - Allergens to mold spores
- Colonization & Disease i.e. when fungi colonize us causing disease
Describe the general characteristics of Fungi.
- Eukaryotic pathogen i.e. contains membrane bound organelles
- Very similar to human cells, making fungi challenging to treat (fewer targets for therapy) w/ two important differences:
○ Cell wall (that is also different from bacteria)
○ Membrane sterol composition (ergosterol vs. cholesterol)
Which fungi contains a capsule?
Cryptococcus neoformas
What are the functions of the fungal cell wall?
To provide:
- Shape
- Rigidity
- Strength
- Protection from osmotic shock
Describe the structure of the fungal cell membrane.
- Typical phospholipid bilayer
- Unique sterol composition that contains “ergosterol (instead of cholesterol),” which serves as the chemotherapeutic target of antifungal drugs
What are the two general categories of fungi?
- Yeast
- Molds (stuff growing on counter, refrigerator, strawberries)
Dimorphic
Fungi that can grow as both yeast & molds–many pathogenic fungi are dimorphic
List the characteristics of yeast.
- Unicellular
- Spherical or ellipsoid shape
- Reproduce by budding (buds are called “blastoconidia”)
- Some form pseudohyphae
What is a pseudohyphae?
Pseudohyphae= when yeast buds never really separate; chains of buds that look like hyphae in mold
What is a germ tube?
Germ Tube= a characterstics pseudophphae that looks like a bud w/ long extension or spoon
- Canida albicans can form a “germ tube” in the presence of serum
What are the different structures that mold can form?
- Hyphae= individual strands of mold
- Mycelium= a mass of intertwined hyphae
○ Can be vegetative or aerial - Septa= cross-walls that divide the hyphae into segments
How can mold reproduce?
- Sexually= spores
- Asexually= conidia
○ Micro= small
○ Macro= big
○ Chlamydo= spore formed in strand of hyphae
How are mold infections diagnosed?
Visually–there aren’t many biochemical tests for mold (vs. bacteria)
What are the different types of fungal infections?
- Superficial mycoses= infection of the outermost layers of skin & hair
- Cutaneous mycoses= infection which extends deep into the epidermis as well as invasive hair & nail infections
○ Most common - Subcutaneous mycoses= infections involving the dermis, subcutaneous tissues, muscle, & fascia
- Systemic mycoses= infections that originate in the lung but may spread to any organ in the body
- Opportunistic mycoses= infection associated with immunosuppressed individuals
What is the host response to fungal infection?
- Innate immune system= generally sufficient to prevent infection
○ Intact skin
○ pH
○ Competition w/ normal bacterial flora
○ Epithelial turnover
○ Dissicated (dry) nature of stratum corneum
○ Mucous membranes have antimicrobial peptides & ciliated cells - Neutrophils & macrophages are both capable of destroying or damaging fungal spores or hyphae
What is the role of the adaptive immune system to fungal infection?
- Cell-mediated (T-cell) is important (esp. INF-gamma production)
- Humoral (Antibody) plays a very small role
How do antifungal drugs differ from antibacterial drugs?
- Fewer antifungals available b/c of similarity to human cells
- Drugs are more toxic
What are some of the targets of antifungal drugs?
B-Glucan & Ergosterol (Cell wall & plasma membrane)
What is Squalene epoxidase?
Squalene epoxidase= enzyme involved in ergosterol synthesis
What class is amphotericin B?
- Polyene (binds to ergosterol & directly disrupts by causing a pore to form in the membrane–>osmotic disruption)
- Formerly the only polyene
What is the mechanism of echinocandins?
Cell wall synthesis inhibitors (B-glucan)
What is the limitation of the echinocandins?
Can only be used for fungi w/ a high concentration of B-glucan in cell wall
What is the problem with visual diagnosis of fungal infections in the lab?
Lots of mold in the environment can lead to contamination of the sample
