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MIMM 211 > Lecture 20: Fungi IV > Flashcards

Lecture 20: Fungi IV Flashcards

1
Q

What is tinea?

A

A dermatophyte infection

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2
Q

What are the 3 types of tinea?

A

Tinea pedis, tinea unguium, tinea corporis

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3
Q

Tinea pedis is also known as […]

A

Athlete’s foot

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4
Q

What is the most common fungal infection of all humans?

A

Tinea pedis

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5
Q

How is tinea pedis treated? Is it easy to treat?

A

It is treated using topical antifungal therapy for 10-14 days. It can be treated, but recurrence is common.

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6
Q

What part of the body does tinea unguium affect?

A

The nail

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7
Q

Is tinea unguium easy to treat? How is it treated?

A

No, it is difficult to eradicate. It is treated with 3-6 months of oral antifungals

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8
Q

What part of the body does tinea corporis affect?

A

The skin

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9
Q

Tinea corporis is also called […]

A

Ringworm

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10
Q

Is tinea corporis easily treatable? How is it treated?

A

It is easily treatable with topical antifungal therapy

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11
Q

What is the major food source of tinea? How does this affect where it colonizes?

A

It is keratin - this is why it likes the hair, nails, and skin, which are all high in keratin.

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12
Q

What type of infections do tinea cause? Why?

A

Only superficial, because they eat keratin and thus have no need to go into the organs and cause systemic infection.

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13
Q

What are the 2 ways to diagnose dermatophytes under a microscope? Include technique and what it shows.

A

Using a skin/hair/nail scraping sample:
1. Use of potassium hydroxide to show hyphae in human cells
2. Use calcofluor to stain chitin

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14
Q

What type of disease is chromoblastomycosis?

A

A subcutaneous mycoses

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15
Q

What is chromoblastomycosis?

A

A chronic fungal infection of the skin and subcutaneous tissue

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16
Q

What is the typical cause of subcutaneous mycoses?

A

Traumatic inoculation by something like a splinter, getting scratched by thorns, etc.

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17
Q

What is the telltale sign of chromoblastomycosis?

A

Dematiaceous molds, meaning the presence of melanin in the cell wall due to spores/hyphae.

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18
Q

How is chromoblastomycosis typically diagnosed?

A

By sclerotic bodies (copper penny bodies), which are stained lesions with potassium hydroxide. They are resting spores.

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19
Q

How dangerous is chromoblastomycosis? Why?

A

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.

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20
Q

What type of disease is eumycotic mycetoma?

A

A subcutaneous mycoses

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21
Q

What is eumycotic mycetoma?

A

Chronic cutaneous and subcutaneous infection with swelling and grainy discharge.

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22
Q

How dangerous is eumycotic mycetoma? Why?

A

It is invasive and destructive of muscles and bones, as they thrive in 37 degrees.

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23
Q

How is eumycotic mycetoma typically diagnosed?

A

By the presence of granules, which are macrocolonies of fungi

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24
Q

What types of individuals are affected by opportunistic molds?

A

Immunosuppressed patients only

25
Q

What is the most common opportunistic mold?

A

Aspergillus fumigatus

26
Q

What are the typical symptoms of diseases cased by opportunistic molds?

A

Pulmonary infection by inhalation of airborne spores with subsequent dissemination. They are very aggressive.

27
Q

Where is Aspergillus mold typically ofund?

A

On decaying material/soil

28
Q

What kind of infection is Aspergillus fumigatus?

A

Systemic mycoses

29
Q

What are the 3 steps of infection by aspergillus fumigatus?

A
  1. Alveolar infection
  2. Angioinvasion
  3. Dissemination
30
Q

Describe the 3 steps of invasion by aspergillus fumigatus.

A
  1. Alveolar infection: inhale airbone conidia, which are endocytosed into pulmonary epithelial cells. They germinate to form hyphae.
  2. Angioinvasion: these hyphae penetrate the blood vessel by inducing damage to endothelial cells
  3. Dissemination: hyphal fragments adhere to the luminal endothelial cell surface before damaging cells and continuing extravascular invasion of deep organs.
31
Q

What are the 2 signs of Aspergillus in the lungs? What do they indicate?

A
  1. Cavity in lung = fungal colony
  2. Redness around lung = enzymes pumped out to degrade tissue
32
Q

What are the 3 major targets of antifungal agents?

A

Ergosterol synthesis, cell wall synthesis, and DNA synthesis

33
Q

Antifungals that target the synthesis of ergesterol are called […]

A

Azoles and polyenes

34
Q

What is the impact of azoles and polyenes on the fungus?

A

It makes the cell membrane excessively permeable by preventing the synthesis of ergesterol.

35
Q

How do polyenes work as antifungals?

A

They bind to ergesterol in membranes and form pores that allow the cell contents to leak out.

36
Q

Give an example of a polyene and how it is produced.

A

Amphotericin B: produced by Streptomyces bacteria, toxic to humans

37
Q

How do azoles work as antifungals?

A

They inhibit 14-alpha demethylase, a key enzyme to synthesize ergesterol. This causes toxic intermediates to accumulate in the membrane.

38
Q

Give 2 examples of azoles and the types of infections they treat.

A

Imidazoles: treat superficial mycoses
Triazole: treat systemic fungal infections

39
Q

What is the target of 5-flucytosine (5-FC)?

A

DNA synthesis

40
Q

Explain how 5-FC works.

A

It is a pro drug that gets converted by fungal cytosine deaminase into 5-FU, which inhibits DNA chain synthesis.

41
Q

What is the meaning of 5-FC being a pro drug?

A

It only becomes active if a fungus activates it.

42
Q

Name a side effect of 5-FC.

A

Bone marrow suppression

43
Q

Name a limitation of 5-FC.

A

Resistance developments within days, so it is only useful in combination therapy

44
Q

What do echinocandins target as antifungals?

A

B-glucan, the major component of the cell wall in fungi.

45
Q

How do echinocandins work as antifungals?

A

They inhibit glucan synthase, which disrupts cell wall synthesis and causes wall fragmentation.

46
Q

How are echinocandins typically produced?

A

They are typically fungal secondary metabolites that are used to kill competing fungi.

47
Q

Name a limitation of echinocandins and name 3 fungi that are unlikely to be affected by it.

A

They are not useful on fungi with low levels of beta-glucan, such as crytococcus, histoplasma, and zygomycetes.

48
Q

Name 3 fungal plant infections?

A

Dutch Elm disease, Rhytisma, Potato Blight

49
Q

What species of fungus causes Dutch Elm disease?

A

Opiostoma species

50
Q

How does dutch elm disease get spread?

A

Fungus invades wood and sporulates in burrows to be picked up by beetles, which spread it to the next tree.

51
Q

How does dutch elm disease work?

A

It blocks the xylem and phloem, which starves out the tree.

52
Q

Where is dutch elm disease a major issue?

A

In North America - notably, Chicago

53
Q

What types of plants does Rhytisma infect?

A

Yellow maple leaves (NOT red)

54
Q

What is the telltale sign of Rhytisma?

A

Tar spots, which contain spores, on leaves.

55
Q

How does Rhytisma spread?

A

Rain allows the spores in tar spots to go into the air and reinfect another leaf.

56
Q

Why are there no more sugar maple trees on Mount Royal?

A

In the 1960s, Norwegian yellow maple were planted, which are susceptible to tar spot and thus did not survive.

57
Q

The potato blight is connected to which major historical event?

A

The Great Irish Famine

58
Q

What fungus caused the potato blight?

A

Phytopthora infestans, a water mold

MIMM 211 (38 decks)

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