Fungus (complete)

Question 1

Describe the characteristics of fungi with respect to morphology, cell composition, and biochemical functioning

Answer 1

• Heterotrophic – no chlorophyll
• Size: ranges from 3micro to several hundred ft
• Reproduction: sexual and asexual, unicellular and multicellular
• Rigid walls: chitin!!
• Sterol cell membrane: ergosterol
• Polysacch capcule in some

Question 2

Explain why fungi differ from bacteria, plants, and animals

Answer 2

• Ergosterol! very specific to fungi

Not cholesterol :DDD

Question 3

Explain the differences between yeast and hyphal forms of fungi (molds) and recognize that some organisms may be dimorphic

Answer 3

Y:

• unicellular
• asexual reproduction (fission, budding)
• shape varies (round, oval)
• colonies often creamy, pasty
• can form pseudohyphae

H:

• Tubular filaments
• Multicellular
• Form a mycelial mat! Elongation
• Typically branching

Question 4

Describe how direct examination is used to diagnose fungal infections

Answer 4

• look under microscope
• scrap skin and add to slide w/ the following agents

KOH
Chlorazol black stain
India ink
Wood’s light

Question 5

Describe how cultures are used to diagnose fungal infections

Answer 5

• What is the grow medium?
• What are the characteristics? (surface, edges, radial grooves, color of colony, color of converse/reverse)
• Lactophenol cotton blue examination

Question 6

Describe how tissue is used to diagnose fungal infections

Answer 6

• Some fungus grows directly in tissue

- Some can only grow on the culture

Question 7

What are other advanced techniques that may be used for certain infections or in specific circumstances?

Answer 7

• Serological

- PCR

Question 8

Describe the mechanism of action of polyenes

Answer 8

“polyenes punch holes in cell membrane”

Question 9

Describe the selective inhibition associated with polyenes

Answer 9

Bind to and inhibit ergosterol assembly

Won’t attack human cells!!

Question 10

What is an example of polyenes?

Answer 10

Amphotericin

Question 11

Describe the mechanism of action of azoles/triazoles

Answer 11

Interfere w/ ergosterol synthesis via 14-demethylase pathway

Question 12

Describe the selective inhibition of azoles/triazoles

Answer 12

Focuses on esgosterol synthesis pathways (not in humans)

Question 13

What is an example of azoles/triazoles?

Answer 13

Efinaconazole, luliconazole

Question 14

Describe the mechanism of action of allylamines/benzylamines

Answer 14

• Fungacidal drug
• Inhibits squalene epoxidase => blocks ergosterol synthesis
• Squalene just accumulates => fungal cell death

Question 15

Describe the selective inhibition of allylamines/benzylamines

Answer 15

Focuses on ergosterol synthesis (at an early point in synthesis)

Question 16

What is dimorphism?

Answer 16

• Specific fungi may grow in 2 different forms

- Depends on environmental stimulus (often temperature)

Question 17

What are examples of classic thermal dimorphic fungi?

Answer 17

Some Can Have Both Phases

1) Sporothrix schenckii
2) Coccidioides immitis
3) Histoplasma capsulatum
4) Blastomyces dermatitidis
5) Paracoccidioides basiliensis

Question 18

Describe the morphology of Conidium

Answer 18

• An asexual spore

- come off aerial hyphae (can be macro or micro)

Question 19

Describe the morphology of Sporangium

Answer 19

• An asexual spore
• have membranous sac
• looks like a lollipop

Question 20

Describe the morphology of Chlamydospores

Answer 20

• An asexual spore
• fungi version of bacterial spores (protect its genetic material for a long time)
• resistant to adverse enviro conditions when its under stress
• don’t stick out — fluid as either terminal or intercalary

Question 21

Describe the morphology of Arthrospores

Answer 21

• An asexual spore
• like a spine/vertebrae
• grow in culture

Question 22

Describe the morphology of Spherules

Answer 22

• An asexual spore
• grow in tissue
• filled w/ small endospores

Question 23

Describe the morphology of Blastoconidia

Answer 23

• An asexual spore
• small buds seen in yeast
• divide asymmetrically