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17 Cards in this Set
- Front
- Back
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What are mycoses? And why do they not occur often?
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– Mycoses are fungal diseases which are common in humans
– Few fungi cause disease as they: 1. Need to grow in low oxygen 2. Have to survive the effective humman immune system 3. Have to survive at 37 Degrees |
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What is the basis for mycoses classification?
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Based on taxonomy:
1. Superficial 2. Subcutaneous 3. Systemic |
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What is a superficial mycoses? Example?
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A dermatophytic (infects skin) fungal disease.
Epidermophyton flocossum is an example. – Causes Tinea Pedis (athletes foot) |
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What are subcutaneous mycoses? Example?
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Wound and mucosa infections which spread through the lymph system.
Candida albicans is an example. – Causes Thrush – Dimorphic yeast form turns into invasive hyphae at 37 degrees – 50% incidence An opportunistic mycoses - develops in immunocompromised, stressed etc. |
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What are systemic mycoses? What are the 2 different types of systemic mycoses? Examples of each?
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Fungal diseases which infect the entire body.
1. Invasive Opportunist – Yeast form attacks immuno–compromised individuals – E.g. Penicillum marneffei which causes penicillosis, a significant disease in AIDS patients 2. Primary Pathogen – Disease which occurs when there are high enough doses – E.g. P. brasiliensis, a wide spread disease in Central and South America which causes a progressive disease of the lung and mouth/nose mucosa |
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What is Aspergillus fumigatus and who is typically the target of its disease?
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– Invasive opportunist fungus which attacks immuno–supressed individuals (e.g. organ transplant patients)
– Abundant in environment and inhalation in large numbers can cause allergic hypersensitive response known as Farmer's Lung |
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What is Cryptococcus Neoformans? How does it resist attack?
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– Common and Infectious basidiomycete yeast with over 1,000,000 cases and 500,000 deaths per year
– C.gattii is an example of a primary pathogen – Uses host dopamine for nutrition and melanin to help resist immune attack |
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Why are fungal diseases hard to treat? What are the 4 main drugs used in antifungal therapy?
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– Hard to treat as Fungi are eukaryotes and are close relatives of animals, and treatment must be target to a specific species and site of disease
1. 5–flucytosine – Mimics uracil, thereby binding and blocking nucleic acid synthesis, but Fungi can become resistant to this very quickly 2. Azoles – Blocks ergosterol (similar to cholesterol) synthesis, disrupting its membrane 3. Griseofulvin – Fungistatic against dermatophytes – Binds to fungal microtubules and inhibits mitosis 4. Polyenes – Disrupts membrane integriy (e.g. Nystatin) – Amphotericin B intravenously for systemic infections (this has side effects) |
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What are the 7 stages of fungal evolution in order of development?
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1. Protist
2. Choanoflagellate 3. Microsporidia 4. Chytridiomycota 5. Zygomycota 6. Ascomycota 7. Basidiomycota |
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What are microsporidia? How do they invade cells?
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– Minute obligate parasite (needs host)
– No mitochondria/flagella – Spores can be ingested by humans – Cell walls stain with calcofluor (high chitin content) – Invades cells through polar tubes which inject sporoplasm (parasite – wall) |
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What are chytridiomycota and their unique features?
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– Ancient fungi which are either soil or aquatic borne
– Have motile zoospores (Posterior flagella) – Limited coenocytic (no regular septa) mycelium |
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How are zygomycota different from chytridiomycota? Describe the asexual and sexual life cycles of zygomycota.
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– Zygomycota do not have motile zoospores however are also coencytic
Asexual: reproduce by mitosis which creates sporangiospores, these are packaged within sporangium, the spore–enclosing structure Sexual: 1. 2 zygospores (sexual) which are of a compatible mating type, anastomose. 2. These cells then undergo plasmogamy which creates a heterokaryonic (unfused nuclei) zygosporangium body with multinucleate zygospores 3. The nuclei within the zygosporangium then undergo karyogamy, forming multiple 2n spores 4. These spores undergo meiosis to become n and then germination occurs with the spores being released |
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How are ascomycota different from zygomycota? What is an example of ascomycota? Describe its asexual and sexual life cycles.
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– Ascomycota differ in that they have a dikaryon (n+n) stage and have regular septa
– They have a sac–like structure – E.g. Truffles Asexual: Hyphae form conidia (asexual spores) which fall off and join another colony or starts one on its own Sexual: 1. 2 Ascogonium (sexual reproductive structure) fuse through plasmogamy to form a heterokaryon 2. Heterokaryon gets partitioned in to dikaryon mycelium 3. Mycelium undergo karyogamy to form 2n asci 4. Asci undergo meiosis to form n asci which undergo mitosis to form an ascus with around 8 ascospores |
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How are basidiomycota different from ascomycota? What is an example of basidiomycota? Describe its sexual life cycle.
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– The asexual conidia form of reproduction is similar however it is much more rare
– The Basidium (sexual reproductive structure) is club like not a sac – Similarly septate – E.g. Mushrooms Sexual: 1. Basidium releases basidiospores (sexual spores) which can form colonies of hyphae 2. Crossing of compatible mating type hyphae leads to anastomosis forming dikaryon (n+n) hyphae. These hang as gills under the basidiocarp. 3. Karyogamy then produces 2n basidium 4. Meiosis and mitosis produces large number of genetically distinct n basidiospores. |
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What are mycotoxins and its 5 main types?
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– Secondary metabolites of fungi
1. Aflatoxins – Toxic and carcinogenic – Can cause liver damage/cancer – E.g. Aspergillus fumigatus 2. Fumonisins – Common grain mould – Associated with cancer – E.g. Fusarium moniliforme 3. Ergots – Contain lysergic acid, which causes hallucinations – Cause gangrenous ergotism OR – Cause convulsive ergotism – E.g. Claviceps purpurea 4. Amatoxins – E.g. Amanita phalloides (death caps) – Cause cholera–like diarrhea 5. Trichothecene – E.g. Fusarium spp. – Livestock will not eat contaminated food |
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How are fungi, as allergens, spread in outdoor vs. indoor environments.
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Outdoor:
– High mould exposure in summer/autumn – Ryegrass pollen in spring Indoor: – High humidity and condensation, low ventilation, enables growth |
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How can fungi be used in drugs? Give 3 examples.
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– The metabolites of fungi can be useful in treating ailments
1. Penicillin 2. Cephalosporin 3. Anti–tumour agents |
