Yeasts and Moulds Flashcards
Mycology: study of
fungi
Fungi group:
Macroscopic and microscopic organisms
Microbiology includes ONLY microscopic fungi (yeasts and moulds)
fungi distrubution
Widely distributed
>100,000 species
Types of Metabolism - Nutrition
Like animals, incapable of producing food
Chemoheterotrophs – use organic chemical substances as sources of energy
Saprophytes - obtaining nutrients from dead organic material
Oxygen requirements
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
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 (HYPERTONIC)
Can grow in low moisture content
Can metabolize complex carbohydrates
Microscopic fungi
Pro, Euk and Acellular
- Prokaryotic cells
Bacteria/Arachea - Eukaryotic cells
Fungi (yeasts/moulds)
Parasites (protozoa/helminths) - Acellular structures (not made of cells)
Viruses
Prions
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
What is the difference between yeasts and moulds?
Antifungal drugs
Fungal vs mammalian cells
Presence of a cell wall
Plasma membrane possesses different sterols
Containing ergosterol and not cholesterol [Excellent selective targets for antifungal drugs]
Presence of vacuoles
Large compartments for storage of molecules, protein degradation
Cell wall in fungi
Fungal cell wall
Chitin layer, a long-chain polymer of N-acetylglucosamine (NAG)
Glucans (polysaccharides of D-glucose monomers) network
Mannoproteins (glycoproteins) on the external side
Plasma membrane in fungi
Fungal plasma membrane
Ergosterol is peculiar to fungal cells
Target for selective antifungal drugs
- what are the two classes?
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)
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)
What are the Harmful effects of fungal microorganisms?
Food spoilage
Contamination of pharmaceutical preparations
Causing diseases > MYCOSES
Mycoses – Overview
a) SPREAD = generally from the environment to people (by spores)
By spores (moulds) or direct contacts (yeasts)
Limited person-to-person spread
b) ENTRY SITES = Skin - direct contact, cuts, splinters
Lungs - inhaling spores
c) VIRULENCE FACTORS = Mycotoxins,
Enzymes
Types of fungal infections
SUPERFICIAL - outer skin layer or on hair shafts caused mostly by yeasts - Black Piedra Dandruff
CUTANEOUS - Affects keratin-containing tissues (hair, nails, skin) - ringworm, athlete’s foot
SUBCUNTANEOUS - Chronic infection of subdermal tissues may require surgical intervention - sporotrichosis
SYSTEMIC - infection deep within body, affects many tissues and organs - Blastomycosis
OPPURTUNISTIC - Caused by normal microbiota or fungi that are not usually pathogenic (immune compromised patients) - Candidiasis, Aspergillsosis
Mycoses - patients at risk
- Impaired immune system
- Surgery and long-term use of corticosteroids
- Indwelling catheters
- Chemotherapy for malignant cancer
- Solid organ transplantation
Yeasts are ___cellular and non-filamentous organisms with ____/_______shape
uni
oval/spherical
How do yeasts reproduce?
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
Clinically relevant yeasts
Genus Candida is the most clinically relevant yeast
Multiple species that can cause diseases (C. albigans, the most common)
What are polymorphic yeasts?
A common change in the genetic code in DNA
Pseudohyphae may be formed
budding yeast cells that remain attached to each other
Normal microbiota / opportunistic infections
Candidanormally 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 disease can Candidasis cause?
Oral candidiasis/thrush
Candida accumulates on the lining of your mouth (creamy white deposit on tongue or inner cheeks)
Vaginal candidiasis/thrush
Symptomatic inflammation of the vagina
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
Pathogen with low virulence
Cryptococcusis 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)
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)
Why 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)
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
What role do spores play in the reproduction of 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
Aspergillosis = found in soil, on plants
2 species that can cause aspergillosis (A. fumigatus and A. flavus)
Aspergillosis = found in soil, on plants
2 species that can cause aspergillosis (A. fumigatus and A. flavus)
Clinical Manifestations
Several different types of aspergillosis - people at risk (Immunocompromised)
Pulmonary aspergillosis the most common
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
- toxicity is observed, especially in chronic infection (long treatments)
- Cell wall and ergosterol (molecules and enzymes involved in different synthesis steps ) are good examples
Targets of different classes of anti-fungal drugs - revise diagram on lec 5 microbiology slide 25
Voriconazole is the treatment of choice for aspergillosis
Within the class of AZOLES – targeting synthesis of ergosterol
Echinocandins (Caspofungin) are the treatment of choice for invasive candidiasis
Echinocandins – targeting synthesis of glucans – component of the cell wall
(^NICE)
