DD Introduction to Fungal Pathogens

Question 1

Fungi characteristics

Answer 1

• Eukaryotic, aerobic, unicellular or filamentous, heterotrophic, and encased in rigid cell wall.
• Reproduce via sexual or asexual means
• It also has a cell membrane inside the cell wall which contains ergosterol.

Question 2

Why are fungi not like bacteria?

Answer 2

has membrane bound organelles

Question 3

Why are fungi not like plants?

Answer 3

lack chlorophyll and are not photosynthetic

Question 4

Why are fungi not like animals?

Answer 4

It has a cell wall! (made of chitin and cellulose)

Question 5

Describe three means for categorizing fungi. Can they be subclassified?

Answer 5

1. Linnean
2. Functional Superficial fungal infections
3. Functional Deep fungal infections

Yes - Fungal species may be subclassified as saprobes, symbionts, commensals or parasites

Question 6

Examples of fungi that cause Superficial fungal infections and what they utilize for growth

Answer 6

DERMATOPHYTES
· Hyphal fungi utilizes keratin as a substrate for growth

CANDIDA
· Yeast that prefers glucose of interstitial fluids

PITYROSPORUM
· Yeast that prefers breakdown products of sebum

Question 7

Yeast vs Hyphae

differences between morph forms?

Answer 7

Yeast forms→ round and oval

Hyphal forms (mold) → filamentous growth form (plural = mycelium), often branched and grow by apical extension.

Question 8

Do yeast or hypha have septa?

Answer 8

Hypha - but can be nonseptate as well

Question 9

Yeast vs Hyphae

which one is unicellular?

Answer 9

Yeast - unicellular

Hyphae - multicellular

Question 10

Yeast vs Hyphae

Reproduction?

Answer 10

Yeast - reproduce by budding or fission

Hyphae - reproduce by formation of spores or conida (looks like a rake)

Question 11

Two types of conida spores produced by hyphae

Answer 11

Macroconidium (large multinucleated spore)

Microconidium (small unicellular spore)

Question 12

Rhizoids

Answer 12

specialized forms of hyphal elements that grow like roots from larger hyphae

Question 13

pseudohyphae

Answer 13

elongated yeast linked together like sausages, and do not have cytoplasmic connections between the compartments.

Question 14

Which species of fungi are dimorphic and exist in yeast or hyphae?

Answer 14

o Some Can Have Both Phases = (For thermal dimorphic species)

- Sporothrix schenkii
- Coccidioides immitis
- Histoplasmosa capsulatum
- Blastomyces dermatitides
- Paracoccidiodes brasiliensis

Question 15

morphology of the basic forms of asexual spores.

Answer 15

1. CONIDIA
2. SPORANGIA
3. CHLAMYDOSPORES
4. ARTHROSPORES
5. SPHERULES
6. BLASTOCONIDIA

Question 16

Explain the morphology of the asexual spore:

CONIDIA

Answer 16

Born off of aerial hyphae (upward projecting hyphae) called conidophores.

May be macroconidium (large and multinucleated) or microconidia (small and unicellular).

Question 17

Explain the morphology of the asexual spore:

SPORANGIA

Answer 17

Similar to macroconidia, except spores are enclosed in membranous sac that can break from the sporangiophore (almost like a stalk) and release a sporangium.

Question 18

Explain the morphology of the asexual spore:

CHLAMYDOSPORES

Answer 18

Thick walled round spores that are highly resistant to adverse environmental conditions. Terminal one can form at end of hyphae, or intercalary ones along and within hyphae.
Know it’s under stress if you see these.

Question 19

Explain the morphology of the asexual spore:

ARTHROSPORES

Answer 19

Along hyphae, but numerous and elongated (shaped like barrel, ex. Coccidiodes immitis). Inhalation from environment can yield the disease.

Question 20

Explain the morphology of the asexual spore:

SPHERULES

Answer 20

Large, typically in yeast form and filled with endospores

Question 21

Explain the morphology of the asexual spore:

BLASTOCONIDIA

Answer 21

Yeasts that bud asymmetrically.

Question 22

MOA of polyenes

Answer 22

“Polyenes punch holes”

○ Bind to ergosterol (fungicidal)

Question 23

MOA of Azoles/Triazoles

Answer 23

○ Inhibit enzyme 14a-demethylase (enzyme that converts lanosterol to ergosterol); fungistatic.
○ Oral form also interferes with fungal CYP450

Question 24

MOA of Allylamines/ Benzylamines (terbinafine)

Answer 24

○ Inhibit enzyme squalene epoxidase (required for ergosterol synthesis), and leads to accumulation of squalene within fungal cell (toxic!); fungicidal.

Question 25

MOA of Echinocandins

Answer 25

Inhibit synthesis of glucan (in CW of some fungi) by inhibition of 1,3-b glucan synthase.

Question 26

MOA of Flucytosine

Answer 26

interrupts DNA synthesis; fungistatic

Question 27

MOA of Griseofulvin

Answer 27

Disrupts mitotic spindle formation, used in children with tinea capitis b/c of safety record; fungistatic.