Fungi Flashcards

1
Q

What are the types of fungi? What are their properties?

A
mould = also known as hypha and mycelium
- multicellular filamentous organisms
- reproduce by spores 
yeast
- unicellular
- reproduce by budding
mushroom
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2
Q

What is a dimorphic fungi?

A

fungi that occur in both yeast and mycelial forms

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3
Q

What are diseases caused by fungi called?

A

mycosis

- they are generally not communicable = cannot be transferred

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4
Q

What are the general properties of fungi?

A

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

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5
Q

What are the types of fungal diseases?

A

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

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6
Q

How can mycoses be classified?

A

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
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7
Q
What is the difference between 
superficial mycoses
cutaneous mycoses
subcutaneous mycoses 
systemic mycoses
A
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
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8
Q

What is the function of the fungi cell wall?

A
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

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9
Q

What are the properties of mould?

A

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

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10
Q

What are the properties of yeasts?

A

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
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11
Q

How can fungal reproduction occur?

A

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

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12
Q
What are the examples of these types of species 
superficial 
cutaneous 
subcutaneous 
systemic 
opportunistic
A
superficial 
- pityriasis versicolor
cutaneous 
- tinea pedis = athlete's foot
- onychomycosis = nail infection 
subcutaneous 
- chromoblastomycosis
systemic 
- blastomycosis 
opportunistic 
- candidiasis
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13
Q

What are the modes of action for antifungals?

A

impairment of cell wall synthesis
impairment of fungal cell membrane
inhibit nuclear acid synthesis
inhibit fungal mitosis

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14
Q

What drugs inhibit cell walls synthesis? How do the drugs work?

A

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

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15
Q

What drugs impair the cell membrane?

A

polyene macrolide antiobiotics

  • amphotericin B
  • nystatin

azoles

  • imdizaole
  • triazole
  • voriconazole = new generation

terbinafine

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16
Q

How do the polyene macrolide antibiotics that impair the cell membrane work?

A

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
17
Q

How do the azoles that impair the cell membrane work?

A

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
18
Q

What drugs inhibit nuclear synthesis? How do they work?

A

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

19
Q

What drugs inhibit fungal mitosis? How do they work?

A

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

20
Q

What are the mechanism of anti fungal resistance?

A

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