Fungi Flashcards
What are the types of fungi? What are their properties?
mould = also known as hypha and mycelium - multicellular filamentous organisms - reproduce by spores yeast - unicellular - reproduce by budding mushroom
What is a dimorphic fungi?
fungi that occur in both yeast and mycelial forms
What are diseases caused by fungi called?
mycosis
- they are generally not communicable = cannot be transferred
What are the general properties of fungi?
able to grow at low water activity, Aw
are eukaryotes
do not contain chlorophyll = np photosynthesis
are filamentous structures = contain filaments
produce spores
grow as saprophytes = grow on dead or decaying organisms
What are the types of fungal diseases?
allergies
- resulting from hypersensitivity to fungal antigens
example - inhaled fungal spores
mycotoxicoses
- resulting from ingestion of fungal toxins in contaminated food or poisonous mushrooms
mycoses
- resulting from ingestion of living tissue by a fungus
example - skin infection
How can mycoses be classified?
systemic infection - deep
- affecting tissues or organs
superficial infection
- affecting skin, nails, mucous membranes
dermatomycoses
- skin, nails, hair = cutaneous
candidiasis
- mucous membrane of the mouth = thrush
- mucous membrane of the vagina = yeast
- mucous membrane of the skin
What is the difference between superficial mycoses cutaneous mycoses subcutaneous mycoses systemic mycoses
superficial mycoses - affect the skin of the hair shaft - no living tissue is invaded = no cellular response from host cutaneous mycoses = dermatomycoses - cause superficial mycoses - affect skin, hair and nails subcutaneous mycoses - penetrate the epidermis = under the skin systemic mycoses - spread throughout the body - affect tissues and organs
What is the function of the fungi cell wall?
maintain structure protect against mechanical injury prevent osmotic lysis provide passive protection against internalisation of potentially harmful macromolecules determine final morphology of fungus
composed largely of chitin, a polymer of N-acetyl glucosamine
What are the properties of mould?
multicellular organisms
reproduce asexually by spore formation or fragmentation
grow on a wide variety of substances
used in the production of antibiotics and cheese
aerobic organisms
can be killed by mild heat treatments
- mould spores are more resistant to heat
What are the properties of yeasts?
made of a cell wall that contains
- nucleus
- mitochondria
- storage granules
yeast have 3 membranes
- nuclear membrane
- cell membrane
- vacuolatr membrane
often forms a bud
- parent and bud cells contain vacuoles
- vacuoles contain a digestive process and work as a storage unit
- once budding has occurred, a bud scar remains on the cell wall
How can fungal reproduction occur?
growth and spread of hyphae filaments
- mould = grow by fragmentation of filaments
asexual reproductions of spores
- mould
budding - simple cell division
- yeast
some yeast produce spores as a result of sexual reproduction
What are the examples of these types of species superficial cutaneous subcutaneous systemic opportunistic
superficial - pityriasis versicolor cutaneous - tinea pedis = athlete's foot - onychomycosis = nail infection subcutaneous - chromoblastomycosis systemic - blastomycosis opportunistic - candidiasis
What are the modes of action for antifungals?
impairment of cell wall synthesis
impairment of fungal cell membrane
inhibit nuclear acid synthesis
inhibit fungal mitosis
What drugs inhibit cell walls synthesis? How do the drugs work?
echinocandin - caspofungin, micafungn
inhibit beta-1,3- D gluten synthase (enzyme)
- involved in the synthesis of beta-1,3-glucans which are components of the cell wall
- inhibition results in cell lysis due to resistance to osmotic forces being lost
active against candida app
- caspofungin
What drugs impair the cell membrane?
polyene macrolide antiobiotics
- amphotericin B
- nystatin
azoles
- imdizaole
- triazole
- voriconazole = new generation
terbinafine
How do the polyene macrolide antibiotics that impair the cell membrane work?
polyene macrolide antibiotics
- bind to membrane ergosterol in the fungal cell
- alter membrane integrity with leakage of ions and macromolecules causing irreversible fungal cell damage = makes the membrane more permeable
- amphotericin B = golden standard for systemic infection but is toxic via the IV route
- nystatin = primarily used for skin, mouth, esophagus, and vagina infections
How do the azoles that impair the cell membrane work?
imidazoles and triazoles
- block synthesis of ergosterol (sterol needed for cell membrane stability) from lanosterol
- inhibit fungal membrane growth and interfere with membrane-bound enzyme systems
Triazoles
- have greater selectivity against fungi than imidazoles
example
- Miconazole
- Clotrimazole
- Fluconazole
- Ketoconazole
voriconazole
- broad spectrum
- active against fluconazole-resistant invasive Candida and Cryptococcus
- are as effective as amphotericin B but less toxic
What drugs inhibit nuclear synthesis? How do they work?
5-Flucytosine
- used with amphotericin B = prevents resistance, decreases its elimination
5-Flucytosine is converted into 5-fluorouracil
5-fluorouracil inhibits both DNA and RNA synthesis
What drugs inhibit fungal mitosis? How do they work?
Griseofulvin
- binds to intracellular microtubular protein and inhibits fungal mitosis = prevents spindle formation
example
- Griseofulvin is a narrow spectrum antifungal that is used to treat dermatophyte infections of skin and nails
What are the mechanism of anti fungal resistance?
altered drug metabolism
- faster elimination
efflux pumps
- directly pump drugs out of the cell
change in protein target
- change in shape of active site = mutation
prevention of drug entry = makes cell membrane impermeable
