Fungi

Question 1

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

Answer 1

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

Question 2

What is a dimorphic fungi?

Answer 2

fungi that occur in both yeast and mycelial forms

Question 3

What are diseases caused by fungi called?

Answer 3

mycosis

- they are generally not communicable = cannot be transferred

Question 4

What are the general properties of fungi?

Answer 4

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

Question 5

What are the types of fungal diseases?

Answer 5

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

Question 6

How can mycoses be classified?

Answer 6

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

Question 7

What is the difference between 
superficial mycoses
cutaneous mycoses
subcutaneous mycoses 
systemic mycoses

Answer 7

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

Question 8

What is the function of the fungi cell wall?

Answer 8

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

Question 9

What are the properties of mould?

Answer 9

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

Question 10

What are the properties of yeasts?

Answer 10

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

Question 11

How can fungal reproduction occur?

Answer 11

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

Question 12

What are the examples of these types of species 
superficial 
cutaneous 
subcutaneous 
systemic 
opportunistic

Answer 12

superficial 
- pityriasis versicolor
cutaneous 
- tinea pedis = athlete's foot
- onychomycosis = nail infection 
subcutaneous 
- chromoblastomycosis
systemic 
- blastomycosis 
opportunistic 
- candidiasis

Question 13

What are the modes of action for antifungals?

Answer 13

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

Question 14

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

Answer 14

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

Question 15

What drugs impair the cell membrane?

Answer 15

polyene macrolide antiobiotics

• amphotericin B
• nystatin

azoles

• imdizaole
• triazole
• voriconazole = new generation

terbinafine

Question 16

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

Answer 16

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

Question 17

How do the azoles that impair the cell membrane work?

Answer 17

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

Question 18

What drugs inhibit nuclear synthesis? How do they work?

Answer 18

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

Question 19

What drugs inhibit fungal mitosis? How do they work?

Answer 19

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

Question 20

What are the mechanism of anti fungal resistance?

Answer 20

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