W21 Yeasts and Moulds Flashcards
Give examples of macroscopic fungi:
Give examples of microorganisms:
Fungi- Mushrooms and truffles
Microorganisms- Yeasts and moulds
What are Chemoheterotrophs?
Use organic chemical substances as sources of energy
What are Saprophytes?
(saprobionts)
Obtain nutrients from dead organic material
(perform extracellular digestion)
Fungal chemical and physical requirements
Nutritional adaption:
- Grow better at pH of 5
Selective media: Sabouraud Media for fungal growth has 5.5 pH
The acidic condition inhibits bacterial growth (isolate and diagnose
fungi infections) - Grow in high sugar and salt concentration; resistant to osmotic pressure
- Can grow in low moisture content
- Can metabolize complex carbohydrates
Oxygen requirements of Fungi
- Most fungi are obligate aerobes (need oxygen)
- Some yeasts, however, are facultatively anaerobic
(absence/presence of oxygen) and can obtain energy by fermentation
-Saccharomyces cerevisiae responsible for wine alcoholic fermentation
Microscopic fungi
Fungal microorganisms (eukaryotes)
Yeasts Vs Moulds
Yeasts:
* Monocellular. Occasionally organised into pseudohyphae
* Asexual reproduction (mainly budding)
* Form white, smooth, round, uniform colonies
Moulds:
* Pluricellular, organised into hyphae
* Asexual or sexual reproduction (through spores)
* Fuzzy colonies with a variety of colours
Main differences in the cellular composition
of fungi and bacteria:
Fungi vs Bacteria
Cell Type: Eukaryotic VS Prokaryotic
Cell Membrane: Sterol present VS Sterols absent
Cell Wall: Glucan and Chitin (no peptidoglycan)
VS Peptidoglycan
Nucleus: Present VS Absent
Organelles: Present VS Absent
Size Bigger: (2-10 μM) VS Smaller (0.2-5 μM)
Fungi differences to mammalian cells:
- Presence of a cell wall
- Plasma membrane possesses different sterols
(Containing ergosterol and not cholesterol - Presence of vacuoles)
(Large compartments for storage of molecules, protein degradation)
=Excellent selective targets for antifungal drugs
Cell wall in fungi
- Chitin layer, a long-chain polymer of N-acetylglucosamine (NAG)
- Glucans (polysaccharides of D-glucose monomers)
network - Mannoproteins (glycoproteins) on the external side
Target for selective antifungal drugs:
* Echinocandin (e.g. Caspofungin), targets the synthesis of glucans
Plasma membrane in fungi
It is the target for which types of drugs? (2)
Fungal plasma membrane:
Ergosterol is peculiar to fungal cells
Target for selective antifungal drugs:
2 classes of drugs
1. Polyenes (e.g. nystatin, natamycin, and amphotericin B), targets ergosterol and causes pores in the cell membrane.
2. Azoles (e.g. fluconazole, itraconazole, voriconazole) and allylamines prevent the synthesis of ergosterol (2 distinct steps)
Importance of fungi for humans
Beneficial roles/activities of fungal microorganisms:
Degrading organic materials
Making alcoholic beverages (wine, beer)
Food preparation (bread, some cheeses, soy sauce)
Commercial production of some organic acids (gallic, citric)
Manufacturing of drugs (ciclosporins) and antibiotics (penicillin)
Commensal microbes of normal microbiota (just some of them)
Harmful effects of fungal microorganisms (3)
Food spoilage
Contamination of pharmaceutical preparations
Causing diseases = MYCOSES
Harmful effects of fungal microorganisms (3)
Food spoilage
Contamination of pharmaceutical preparations
Causing diseases = MYCOSES
What is Mycoses?
How is it spread:
What are the Entry sites:
What are the virulence factors:
A disease caused by a fungus (fungal infection)
Spread: generally from the environment to people (by spores)
By spores (moulds) or direct contacts (yeasts)
Limited person-to-person spread
Entry sites:
* Skin - direct contact, cuts, splinters
* Lungs - inhaling spores
Virulence factors:
* Mycotoxins
* Enzymes
Types of fungal infections
What are Superficial infections?
Outer skin layer or on hair shafts caused mostly by yeasts