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
What are Cutaneous infections?
Affects keratin-containing tissues
(hair, nails, skin)
Where is a Subcutaneous infection situated?
What are some examples? (For info)
Underneath the dermis (and epidermis)
Burns, abscesses, tumours
Chronic infection of subdermal tissues may require surgical intervention
What are Systemic infections?
Infection deep within body, affects many tissues
and organs
What are Opportunistic infections?
Caused by normal microbiota or fungi that are not usually pathogenic (immune compromised patients)
Mycoses (fungal infection) risk factors for patients? (5)
Solid organ transplantation
Indwelling catheters
Chemotherapy for malignant cancer
Surgery and long term use of corticosteroids
Impaired immune system
What are Yeasts? (Inc shape)
How do they reproduce? (2)
- Unicellular and non-filamentous organisms with oval/spherical shape
Reproduction:
* Asexual reproduction (1 parent involved)
Most by budding
New organism develops from an outgrowth (bud)
ASYMETRICAL cell division at one particular site
Parent remains the same
Others by binary fission (SYMMETRICAL division) 2 daughter cells
What is the most clinically relevant yeast?
What are examples of polymorphic yeast?
Genus Candida
- Polymorphic yeast
- Pseudohyphae may be formed
- budding yeast cells that remain attached to each other
Normal microbiota / opportunistic infections:
* Candida normally lives in the oral cavity, GI and genital tracts (normal microbiota)
* Most common cause of fungal opportunistic infections
-immunocompromised patients or when the microbiota is altered (overgrowth)
What is Candidasis?
3 types of candidiasis?
Candidasis – any infections caused by any species of Candida
* It can affect many areas and develop a wide range of diseases
1. Vaginal
2. Oral/mouth/oesophageal
3. Invasive (gets into bloodstream by medical device)
What is Oral candidiasis/thrush?
- Fungal infection
- Candida accumulates on the lining of your mouth (creamy white deposit on tongue or inner cheeks)
What is an example of a fungal infection?
-Vaginal candidiasis/thrush
* Symptomatic inflammation of the vagina
* Caused by candida ( group of yeasts)
Invasive candidiasis/thrush
Serious infection that could affect many tissues and organs. The severity usually depends on the state of the host’s immune system
Genus Cryptococcus
Genus Cryptococcus:
* 2 species that can cause diseases (C. neoformans, the most common and C. gattii)
Pathogen with low virulence:
Spherical, single cell yeast
Surrounded by a peculiar and unusual polysaccharide capsule
* Cryptococcus is NOT part of normal microbiota
* However, it causes serious infections merely in severely immune compromised hosts
(e.g. meningitis, pneumonia, typical in people with advanced HIV infection/AIDS)
What are Moulds?
Multicellular organisms consisting of threadlike
tubular structures called hyphae
* The hyphae form together to produce a mat-like
structure called a mycelium (fuzzy appearance)
What are the 2 different areas of a mould colony?
- Vegetative mycelium elongates to obtain
nutrients and anchor the mould on the Agar - Aerial mycelium grow on top and have
reproduction function (producing spores)
Mould reproduction
- Reproduction can be sexual (2 parents) or asexual (from 1 parent)
- Mould can reproduce asexually by fragmentation:
Mycelium may fragment into segments, which can grow into new individuals
Spores
- Produce spores asexually or sexually
- Asexual spore production (single parent)
Organism produced by mitosis - Sexual spore production
Involves the fusion of haploid spores (after meiosis) from partner of opposite mating type
Aspergillosis:
What are Genus Aspergillus?
=ubiquitous moulds found in soil, on plants
* 2 species that can cause aspergillosis (A. fumigatus and A. flavus)
What are the 2 types of Aspergillosis?
- Several different types of aspergillosis -
people at risk (Immunocompromised) - Pulmonary aspergillosis the most common
Clinical Manifestations
interstitial pneumonitis or localized wedge-shaped infiltrates
Interstitial pneumonitis or localized ball-
shaped infiltrates (Aspergilloma) - Invasive aspergillus – infection can
spread from lung to heart, brain, kidneys
Targets of different classes of antifungal drugs
Selective toxicity for antifungal drugs:
- More challenging than antibiotics due to similarity with human cells
- Sometimes toxicity is observed, especially in chronic infection (long
treatments)
Good examples of selective fungal targets – Cell wall and ergosterol
(molecules and enzymes involved in different synthesis steps )
How do Yeasts and Moulds reproduce?
Yeasts reproduce asexually, moulds can reproduce either asexually or sexually through the
formation of spores (different functions of bacterial endospores).
How do yeasts reproduce?
Most of them reproduce by budding
Which is not a component of a fungal cell wall?
Peptidoglycan
Gluons
Chitin
Mannoproteins
Peptidoglycan
What term refers to fungal infections deep within the body?
Systemic infections
Give examples of macroscopic fungi:
Give examples of microorganisms:
Fungi- Mushrooms and truffles
Microorganisms- Yeasts and moulds
