Introduction to Fungi Flashcards
Fungi vs. bacteria
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
What is unicellular fungi
Yeast
What are multicellular fungi
Hyphae aka mold form
What is the major reservoir for yeast
Soil
What does it mean to be a saprophte
It is what fungi are- acquiring nutrients from dead or decaying organic matter
What is mycelium
Thick masses of hyphae
What are dimorphic fungi
Fungi that can exist as either mold or yeast
Thermally dimorphiic is what
Changing from mold to yeast form based on temperature (yeast in Vivo)
How do yeast reproduce
Asexually via budding
How do molds and filamentous fungi reproduce
Asexually via conidia (spore) at tip of hyphae or reproduce sexually during times of stress
What is in fungal cell membrane and cell wall
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
Diagnosing fungi diseases broad
Direct microscopic exam or culture, serology, or PCR
What do you look for on a microscope scraping and what is not helpful for fungi
Fungal elements (hyphae and yeast) in scrapings, gram stains not helpful
What stains are helpful for fungi
Potassium hydroxide, India ink, Lactophenol cotton blue, and other special stains for histology
How to culture fungus
Need a special transport medium and thermally dimorphic pathogenic fungi need to be handled in bio-safety cabinet because mold form is contagious
Medium used to grow fungi
Sabouraud’s dextrose agar at room temp (25-30C)
What is diagnosis of mold fungi based on
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
Many serology tests are what
sensitive but not specific
Anti-fungal therapy is difficult why
Because fungi are eukaryotic so they are similar to animal host cells so it is hard to specifically target fungi
Examples of polenes
Amphotericin B and Nystatin
How do polenes work
Bind to sterols (ergosterol) to increase permeability of fungal plasma membrane
What is the down side to Amphotericin B
Had to be given IV and was toxic- binds to proximal tubule epithelial cells in kidney and can cause loss of kidney function
How do Allylamines work
Inhibits enzyme in early step in ergosterol synthesis
How do Azoles work
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
How do Echinocandins work
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
How does Nikkomycin Z work
Blocks synthesis of chitin to lead to osmotic lysis
How does Griseofulvin work
Blocks mitosis of fungal cells and used orally for dermatophyte (skin and nail bed) infections- concentrates in keratinized epithelium, take weeks to work
Do we know how Iodides work
No
Nystatin is a what
oral and topical polyene antifungal drug
