Yeasts & Moulds Flashcards
What is mycology?
the study of fungi
= macroscopic and microscopic fungal organisms
What type of fungi does microbiology include?
*only yeasts and moulds
What are the chemical growth requirements for fungi?
- Incapable of producing food, they are:
▪ Chemoheterotrophs AND saprophytes – use organic chemical substances as
sources of energy
▪ And specifically- obtaining nutrients from dead organic material
What are the oxygen requirements for fungi?
- Mostly obligate aerobes (need oxygen)
- Some yeasts, are facultatively anaerobic - obtaining energy by fermentation
▪ Saccharomyces cerevisiae responsible for wine alcoholic fermentation
What are the nutritional adaptation features of fungi?
- Grow better at pH of 5
▪ Selective fungal media: Sabouraud Media (5.5 pH) inhibiting bacterial growth - Ca grow in hypertonic solution (high sugar/salt concentration)
▪ resistant to osmotic pressure - Can grow in low moisture content
- Can metabolize complex carbohydrates
What type of cells are microscopic fungi (yeasts & moulds)?
eukaryotic cells
What are the general details to know about yeasts?
*▪ Monocellular. Occasionally
organised into pseudohyphae
*asexual reproduction
*for white, smooth, round, uniform colonies
What are the general details to know about moulds?
*pluricellular, organised into hyphae
*asexual or sexual reproduction
*fuzzy and coloured colonies
What are the structural components of fungi ?
cell membrane: sterol present
cell wall: gluten and chitin (no peptidoglycan)
nucleus: present
organelles: present
size: bigger (2-10µm)
What are the differences between fungi and mammalian cells?
*presence of a cell wall
* plasma membrane posses different sterols
-containing ergosterol and not cholesterol
*presence of large vacuoles
-large compartments for storage of molecules, protein degradation.
Describe in detail what is in the fungi cell wall
*chitin layer, a long chain polymer of N-acetylglucosamine (NAG)
*glucans (polysaccharides of D-glucose monomers)
*mannoproteins (glycoproteins) on the external side
This cell wall is target for selective antigfungal drugs
What antifungal drugs target the fungi plasma membrane which has ergosterol in it?
*polyenes (e.g nystatin, natamycin and amphotericin B), targets ergosterol and causes pores in the cell membrane
*azoles (e.g fluconazole, itraconazole, voriconazole) and allylamines prevent the synthesis of ergosterol
What are the beneficial effects of fungi on humans?
▪ 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)
What are the harmful effects of fungi on humans?
*food spoilage
*contamination of pharmaceutical preparations
*causing diseases → mycoses
How are mycoses spread?
- Spread generally from the environment to people (by spores)
▪ By spores (moulds) or direct contacts (yeasts)
▪ Limited person-to-person spread
Where are the entry sites of mycoses?
- Skin - direct contact, cuts, splinters
- Lungs - inhaling spores
What are the types of fungal infections?
- superficial
- cutaneous
- subcutaneous
- systemic
- opportunistic
What is the description/location for: superficial infection
Outer skin layer or on hair shafts
caused mostly by yeasts
What is the description/location for: cutaneous infection?
Affects keratin-containing tissues
(hair, nails, skin)
What is the description/location for:subcutaneous infection?
Chronic infection of subdermal tissues may require surgical intervention
What is the description/location for: systemic infection?
Infection deep within body, affects many tissues and organs
What is the description/location for: opportunistic infection?
Caused by normal microbiota or fungi that are not usually pathogenic (immune compromised patients)
What are the risk factors for patient in regards to mycoses?
- impaired immune system
- surgery and long term use of corticosteroids
- solid organ transplantation
- chemotherapy for malignant cancer
- indwelling catheters
What is the shape of yeasts and the details on their reproduction?
- unicellular and non-filamentous organisms with oval/spherical shape buds
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) → 2 daughter cells
What is the most clinically relevant yeast?
*genus candida
-lives in oral cavity, GI and genital tracts (normal microbiota)
*most common cause of fungal opportunistic infections
-immunocompromised patients or when microbiota is altered (overgrowth)
What are some candidasis infections?
*oral candidasis (thrush)
*vaginal candidasis (thrush)
*invasive candidasis/thrush
-SERIOUS can affect many tissues and organs
What is another clinically relevant yeast?
- genus cryptococcus
*pathogen with low virulence
*not part of normal microbiota
*causes serious infections in severely immunocompromised hosts (meningitis, pneumonia, typical in people with HIV and AIDS)
What is a mould?
- Multicellular organisms consisting of threadlike
tubular structures called hyphae - The hyphae form together to produce a mat-like
structure called a mycelium (fuzzy appearance)
Why are there two 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)
How are spores produced by moulds?
- 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
What are some clinical manifestations of aspergillosis?
- Different types of aspergillosis - people at risk (Immunocompromised)
▪ Interstitial pneumonitis or localized ball- shaped infiltrates (Aspergilloma)
- Invasive aspergillus – infection can spread from lung to heart, brain, kidneys
Why are anti fungal drugs more difficult to produce?
- More challenging than antibiotics due to similarity with human cells - toxicity
is observed, especially in chronic infection (long treatments)
What do yeasts reproduce by?
asexual budding
