L5: General Mycology Flashcards
What is the morphology of fungi?
There are three main groups of fungi based on cell morphology:
- Yeast and Yeast-like
- filamentous (hyphae)
- dimorphic fungi
What is the definition of Yeast and yeast-like fungi?
- Yeasts are round to oval unicellular fungi which reproduce by budding or fission, a progenitor then detached from the mother cell, e.g. (Cryptococcus neoformans).
- Yeast-like is round to oval multi-cellular fungi reproduce by budding but a progenitor remains attached to the mother cell giving a chain of elongated yeast cells called pseudohyphae. e.g. (Candida).
What is the definition of filamentous fungi?
- Filamentous fungi (hyphae) are tubular, branching structures that may or may not be separated by porous cross-walls (septa) forming septated or aseptated hyphae.
- The part of the hyphae that anchor the colony, absorbs nutrients is termed vegetative hyphae.
- The part that projects above & carries the reproductive structure called aerial hyphae.
What is the definition of dimorphic fungi?
Dimorphic fungi exist either as yeast or as filaments depending on the condition of growth.
What are examples of dimorphic fungi?
Coccidioides immitis
Histoplasma capsulatum
paracoccidioides brasiliensis
lastomisis demesis
How do fungi reproduce?
Fungi reproduce by the formation of spores either asexual or sexual
What are the types of asexual spores?
There are two general types of asexual spores:
a. Sporangiospore
b. Conidiospore
What are sporangiospores? And where does it happen?
Some fungi during growth form sac filled with spores.
They are mitotic spores produced within a sac termed sporangium often supported by one hyphae termed sporangiophore and this type of spores exists on non-septated fungi.
What are the types of conidiospores?
- Arthroconidia (Arthrospores): conidia that result from fragmentation of hyphae cell.
- Blastoconidia (Blastospores): conidial formation through a budding process.
- Phialoconidia: conidia that are produced by a (vase-shaped) conidiogenous cell termed a phialide. These spores formed at the terminal part of fertile hyphae.
- Chlamydoconidia (Chlamydospores): large thick-walled resting spores developed from hyphae for existence during long periods of dormancy.
How are sexual spores formed?
During sexual reproduction, haploid cells of compatible strains mate through a process of plasmogamy, karyogamy, and meiosis to form transient diploid——> meiosis of this transient diploid to form sexual spores
What are the types of sexual spores?
- Ascospores
- Basidiospores
- Zygospores
- Oospores
What is the definition of ascospores?
four to eight meiospores form within a sac-shaped structure termed ascus.
What is the definition of basidiospores?
four meiospores usually form on the surface of a specialized club-shaped structure termed basidium.
What are zygospores?
a large thick-walled zygospore develops between two different hyphae.
What are oospores?
a large thick-walled zygospore develops within the same hyphae.
What are the harmful effects of fungi?
- Hypersensitivity reactions due to environmental exposure to fungal spores.
- Infection results from invasion Of tissue and organs.
- Toxicosis (With description)
What are types of fungal toxicoses?
a) Mycotoxicosis: result from accidental consumption of food products contaminated by toxin-producing fungi e.g • Ergot alkaloids toxicosis
• Aflatoxicosis
b) Mycetismus: result from ingestion of fungi containing preformed toxin e.g: • Mushroom poisoning
What is the classification of medically important fungi?
I. Primary pathogenic fungi:
Affect immunocompetent individuals e.g. dimorphic fungi
II. Opportunistic fungi:
Affect immunocompromised individuals e.g. candida (yeast-like)
What is mycosis?
Mycosis means diseases caused by fungi.
What are fungal infections classified according to?
Fungal infections are classified according to affected tissue or organ
What are the types of mycosis?
I) Superficial mycosis
II) Cutaneous mycosis
III) Subcutaneous mycosis
V) Opportunistic mycosis
What is superficial mycosis and what is an example for it?
Strictly surface infections are limited to the outermost layers of skin and hair.
Example:
- Pityriasis versicolor
Caused by Malassezia
Clinically appear as blotchy hypo or hyperpigmented itchy macular lesions usually on the chest, back, abdomen, upper arm.
What is cuteness mycosis and what is an example for it?
Fungal infections that extend deeper into the epidermis, hair, and nail.
Example:
* Dermatophytosis caused by dermatophytes
There are different clinical forms based on site of involvement:
- Tinea capites
- Tinea Barbae
- Tinea unguim
- Tinea pedis
- Tinea corporis
- Tinea cruris
What does Tinea capitis affect? And what are its symptoms?
Affecting the scalp & hair.
Dull gray circular patches of alopecia with itching broken hair.
What does Tinea barbae affect? And what are its symptoms?
Affecting the beard hair.
Edematous, erythematous lesion.
What does Tinea ungium affect? And what are its symptoms?
Affecting the nails.
Thickened, yellow discoloration, lusterless brittle nail.
What does Tinea pedis affect? And what are its symptoms?
Affecting between toes.
Itching, development of small vesicles, rupture, toe webs become macerated, and peels.
What does Tinea corporis affect? And what are its symptoms?
Affecting non-hairy smooth skin.
Advancing rings with scaly center and periphery are inflamed, vesiculated “site of active fungal growth”.
What does Tinea cruris affect?
Affecting the groin, moist areas.
What is subcutaneous mycosis and what is an example for it?
Infection involving the dermis, subcutaneous tissue, muscle, and fascia.
Example: *Mycetoma
What is the definition of myectoma and what is it caused by?
Caused by Madurell, Exophiala.
The chronic subcutaneous infection progresses slowly and burrows into deeper tissue producing abscess which bursts with the formation of chronic sinuses discharging fluid containing granules.
What is systemic mycosis? And what is it caused by?
- Infections involve many organ systems.
Caused by primary pathogenic dimorphic fungi.
What are examples of systemic mycosis?
Histoplasmosis, Blastomycosis,
Coccidioidomycosis, Paracoccidioidomycosis
What is opportunistic mycosis? And what are examples of it?
Group of mycoses caused by saprophytic immunocompromised individuals.
e.g. Candidiasis, Aspergillosis, and Cryptococcosis.
What are the targets of anti-fungal therapy?
There are drugs that act on:
- Cell wall synthesis:
Caspofungin: inhibit 1,3- β glucan synthetase enzyme———->Inhibit cell wall synthesis. - Ergosterol synthesis:
Polyenes: e.g. Amphotericin B, Nystatin: bind firmly to ergosterol in the fungal cell membrane forming pores—>disrupt membrane function—>cell death.
Azoles: interact with cytochrome P450 dependent 14-α demethylase to inhibit demethylation of lanosterol to ergosterol. - Cytoplasmic membrane function:
Polyenes
Azoles - Nuclear division:
Griseofulvin: interact with microtubules—>disrupt mitotic spindle function—>inhibit growth. - Nucleic acid synthesis:
5 fluorocytosine: converted by fungal enzyme cytosine deaminase into 5- fluorouracil which interferes with DNA synthesis. - Protein synthesis: Blasticidin
- Metabolic inhibitors
