Introduction to Fungi

Question 1

Fungi vs. bacteria

Answer 1

Fungi are eukaryotes, membrane bound organelles, slower cell division, different ribosome system (80S), no motility- sessile, not obligate anaerobes, plasma membrane has ergosterol, and cell wall composed of glucans ex.chitin

Question 2

What is unicellular fungi

Answer 2

Yeast

Question 3

What are multicellular fungi

Answer 3

Hyphae aka mold form

Question 4

What is the major reservoir for yeast

Answer 4

Soil

Question 5

What does it mean to be a saprophte

Answer 5

It is what fungi are- acquiring nutrients from dead or decaying organic matter

Question 6

What is mycelium

Answer 6

Thick masses of hyphae

Question 7

What are dimorphic fungi

Answer 7

Fungi that can exist as either mold or yeast

Question 8

Thermally dimorphiic is what

Answer 8

Changing from mold to yeast form based on temperature (yeast in Vivo)

Question 9

How do yeast reproduce

Answer 9

Asexually via budding

Question 10

How do molds and filamentous fungi reproduce

Answer 10

Asexually via conidia (spore) at tip of hyphae or reproduce sexually during times of stress

Question 11

What is in fungal cell membrane and cell wall

Answer 11

Multi-layered (more complex than bacteria) with ergosterol in the plasma membrane, chitin a polysaccharide that provides rigidity and melanin which protects the host from oxidant stress
Most of cell wall-80% is composted of complex polysaccharides called Glucans
Glycoproteins (mannoproteins) make up 20% of cell wall

Question 12

Diagnosing fungi diseases broad

Answer 12

Direct microscopic exam or culture, serology, or PCR

Question 13

What do you look for on a microscope scraping and what is not helpful for fungi

Answer 13

Fungal elements (hyphae and yeast) in scrapings, gram stains not helpful

Question 14

What stains are helpful for fungi

Answer 14

Potassium hydroxide, India ink, Lactophenol cotton blue, and other special stains for histology

Question 15

How to culture fungus

Answer 15

Need a special transport medium and thermally dimorphic pathogenic fungi need to be handled in bio-safety cabinet because mold form is contagious

Question 16

Medium used to grow fungi

Answer 16

Sabouraud’s dextrose agar at room temp (25-30C)

Question 17

What is diagnosis of mold fungi based on

Answer 17

First change the agar to grow at 35-37C to see if the mold form changes to yeast (thermally dimorphic) then
Microscopic appearance of conidia and conidiophores

Question 18

Many serology tests are what

Answer 18

sensitive but not specific

Question 19

Anti-fungal therapy is difficult why

Answer 19

Because fungi are eukaryotic so they are similar to animal host cells so it is hard to specifically target fungi

Question 20

Examples of polenes

Answer 20

Amphotericin B and Nystatin

Question 21

How do polenes work

Answer 21

Bind to sterols (ergosterol) to increase permeability of fungal plasma membrane

Question 22

What is the down side to Amphotericin B

Answer 22

Had to be given IV and was toxic- binds to proximal tubule epithelial cells in kidney and can cause loss of kidney function

Question 23

How do Allylamines work

Answer 23

Inhibits enzyme in early step in ergosterol synthesis

Question 24

How do Azoles work

Answer 24

Inhibit enzyme required to convert lanosterol to ergosterol and the buildup of lanosterol induces a gene that converts lanosterol to toxic sterol, no nephrotoxicity but like many antifungal take a long time to work

Question 25

How do Echinocandins work

Answer 25

Block beta(1,3)D-glucagon synthesis which is a major component of cell wall and inhibits hyphae tip and branch point growth and also results in osmotic lysis

Question 26

How does Nikkomycin Z work

Answer 26

Blocks synthesis of chitin to lead to osmotic lysis

Question 27

How does Griseofulvin work

Answer 27

Blocks mitosis of fungal cells and used orally for dermatophyte (skin and nail bed) infections- concentrates in keratinized epithelium, take weeks to work

Question 28

Do we know how Iodides work

Answer 28

No

Question 29

Nystatin is a what

Answer 29

oral and topical polyene antifungal drug