Lecture 20: Fungi IV Flashcards
What is tinea?
A dermatophyte infection
What are the 3 types of tinea?
Tinea pedis, tinea unguium, tinea corporis
Tinea pedis is also known as […]
Athlete’s foot
What is the most common fungal infection of all humans?
Tinea pedis
How is tinea pedis treated? Is it easy to treat?
It is treated using topical antifungal therapy for 10-14 days. It can be treated, but recurrence is common.
What part of the body does tinea unguium affect?
The nail
Is tinea unguium easy to treat? How is it treated?
No, it is difficult to eradicate. It is treated with 3-6 months of oral antifungals
What part of the body does tinea corporis affect?
The skin
Tinea corporis is also called […]
Ringworm
Is tinea corporis easily treatable? How is it treated?
It is easily treatable with topical antifungal therapy
What is the major food source of tinea? How does this affect where it colonizes?
It is keratin - this is why it likes the hair, nails, and skin, which are all high in keratin.
What type of infections do tinea cause? Why?
Only superficial, because they eat keratin and thus have no need to go into the organs and cause systemic infection.
What are the 2 ways to diagnose dermatophytes under a microscope? Include technique and what it shows.
Using a skin/hair/nail scraping sample:
1. Use of potassium hydroxide to show hyphae in human cells
2. Use calcofluor to stain chitin
What type of disease is chromoblastomycosis?
A subcutaneous mycoses
What is chromoblastomycosis?
A chronic fungal infection of the skin and subcutaneous tissue
What is the typical cause of subcutaneous mycoses?
Traumatic inoculation by something like a splinter, getting scratched by thorns, etc.
What is the telltale sign of chromoblastomycosis?
Dematiaceous molds, meaning the presence of melanin in the cell wall due to spores/hyphae.
How is chromoblastomycosis typically diagnosed?
By sclerotic bodies (copper penny bodies), which are stained lesions with potassium hydroxide. They are resting spores.
How dangerous is chromoblastomycosis? Why?
Not very - it is relatively superficial and non-destructive, because these fungi prefer 35-36 degrees vs 37, so they stay near the outside of the body.
What type of disease is eumycotic mycetoma?
A subcutaneous mycoses
What is eumycotic mycetoma?
Chronic cutaneous and subcutaneous infection with swelling and grainy discharge.
How dangerous is eumycotic mycetoma? Why?
It is invasive and destructive of muscles and bones, as they thrive in 37 degrees.
How is eumycotic mycetoma typically diagnosed?
By the presence of granules, which are macrocolonies of fungi
What types of individuals are affected by opportunistic molds?
Immunosuppressed patients only
What is the most common opportunistic mold?
Aspergillus fumigatus
What are the typical symptoms of diseases cased by opportunistic molds?
Pulmonary infection by inhalation of airborne spores with subsequent dissemination. They are very aggressive.
Where is Aspergillus mold typically ofund?
On decaying material/soil
What kind of infection is Aspergillus fumigatus?
Systemic mycoses
What are the 3 steps of infection by aspergillus fumigatus?
- Alveolar infection
- Angioinvasion
- Dissemination
Describe the 3 steps of invasion by aspergillus fumigatus.
- Alveolar infection: inhale airbone conidia, which are endocytosed into pulmonary epithelial cells. They germinate to form hyphae.
- Angioinvasion: these hyphae penetrate the blood vessel by inducing damage to endothelial cells
- Dissemination: hyphal fragments adhere to the luminal endothelial cell surface before damaging cells and continuing extravascular invasion of deep organs.
What are the 2 signs of Aspergillus in the lungs? What do they indicate?
- Cavity in lung = fungal colony
- Redness around lung = enzymes pumped out to degrade tissue
What are the 3 major targets of antifungal agents?
Ergosterol synthesis, cell wall synthesis, and DNA synthesis
Antifungals that target the synthesis of ergesterol are called […]
Azoles and polyenes
What is the impact of azoles and polyenes on the fungus?
It makes the cell membrane excessively permeable by preventing the synthesis of ergesterol.
How do polyenes work as antifungals?
They bind to ergesterol in membranes and form pores that allow the cell contents to leak out.
Give an example of a polyene and how it is produced.
Amphotericin B: produced by Streptomyces bacteria, toxic to humans
How do azoles work as antifungals?
They inhibit 14-alpha demethylase, a key enzyme to synthesize ergesterol. This causes toxic intermediates to accumulate in the membrane.
Give 2 examples of azoles and the types of infections they treat.
Imidazoles: treat superficial mycoses
Triazole: treat systemic fungal infections
What is the target of 5-flucytosine (5-FC)?
DNA synthesis
Explain how 5-FC works.
It is a pro drug that gets converted by fungal cytosine deaminase into 5-FU, which inhibits DNA chain synthesis.
What is the meaning of 5-FC being a pro drug?
It only becomes active if a fungus activates it.
Name a side effect of 5-FC.
Bone marrow suppression
Name a limitation of 5-FC.
Resistance developments within days, so it is only useful in combination therapy
What do echinocandins target as antifungals?
B-glucan, the major component of the cell wall in fungi.
How do echinocandins work as antifungals?
They inhibit glucan synthase, which disrupts cell wall synthesis and causes wall fragmentation.
How are echinocandins typically produced?
They are typically fungal secondary metabolites that are used to kill competing fungi.
Name a limitation of echinocandins and name 3 fungi that are unlikely to be affected by it.
They are not useful on fungi with low levels of beta-glucan, such as crytococcus, histoplasma, and zygomycetes.
Name 3 fungal plant infections?
Dutch Elm disease, Rhytisma, Potato Blight
What species of fungus causes Dutch Elm disease?
Opiostoma species
How does dutch elm disease get spread?
Fungus invades wood and sporulates in burrows to be picked up by beetles, which spread it to the next tree.
How does dutch elm disease work?
It blocks the xylem and phloem, which starves out the tree.
Where is dutch elm disease a major issue?
In North America - notably, Chicago
What types of plants does Rhytisma infect?
Yellow maple leaves (NOT red)
What is the telltale sign of Rhytisma?
Tar spots, which contain spores, on leaves.
How does Rhytisma spread?
Rain allows the spores in tar spots to go into the air and reinfect another leaf.
Why are there no more sugar maple trees on Mount Royal?
In the 1960s, Norwegian yellow maple were planted, which are susceptible to tar spot and thus did not survive.
The potato blight is connected to which major historical event?
The Great Irish Famine
What fungus caused the potato blight?
Phytopthora infestans, a water mold
