Fungi Flashcards
Are fungi eukaryotic or prokaryotic? What is 1 main difference between fungi and plants?
Eukaryotic
Do not have chlorophyll
What is S. cerevisiae?
Brewer’s/baker’s yeast
What are the 3 classifications of fungi?
Unicellular (yeasts)
Filamentous (moulds)
Dimorphic
What is the metabolic classification of unicellular fungi?
Facultative anaerobes
How do unicellular fungi reproduce?
Asexually by budding
How do unicellular fungi appear on agar?
Produce colonies
What is the metabolic classification of filamentous fungi?
Aerobes
How do filamentous fungi reproduce?
By conidia (asexual spores)
How do filamentous fungi appear on agar?
Produce mycelia
What are dimorphic fungi?
Can switch between unicellular and filamentous forms
How big is the average yeast?
2-3um
Are fungi saprophytes?
Mostly
Give an example of a filamentous fungi
Penicillium
How does filamentous fungi appear under the microscope?
Hyphae and conidia
List the different types of fungi in order from most to least virulent
Dimorphic fungi Dermatophytes Agents of subcutaneous mycoses Opportunists Toxic fungi
Give an example of a dimorphic fungus and the disease it causes
Histoplasma capsulatum
Causes “cave’s disease”
Which of the fungis are primary pathogens?
Dimorphic fungi
Dermatophytes
What makes dimorphic fungi good pathogens?
Can grow as filamentous fungi in environment, yeasts in body
List 3 genera of dermatophytes
Microsporum
Trichophyton
Epidermophyton
What type of fungi cause ringworm?
Dermatophytes
Where do dermatophytes grow?
In keratin tissues (e.g. skin, hair, nails)
How do dermatophytes cause symptoms? Which dermatophytes are more likely to cause symptoms than others?
Release metabolic by-products which can cause symptoms Zoophilic dermatophytes (e.g. Microsporum canis) more likely to cause symptoms than anthropophilic (e.g. Trichophyton rubrum) dermatophytes
What type of fungus causes tinea?
Dermatophytes
Are agents of subcutaneous mycoses generally pathogenic? How are humans innoculated with these organisms?
Low grade pathogens
Innoculated directly onto the skin
What is tinea corporis?
Tinea of the body
Give 3 examples of subcutaneous mycoses
Mycetoma
Chromoblastomycosis
Phaeohyphomycosis
What are bacterial mycetomas called?
Acintomycetoma
What is tinea cruris?
Tinea of the groin
What are fungal mycetomas called?
Eumycetoma
What is the proper name of mycetoma?
Maduromycosis
Give an example of an opportunistic mycoses
Candidiasis (caused by Candida albicans)
What is the most common acintomycetoma?
Nocardia spp.
What is the most common eumycetoma?
Madurella spp.
What are the 3 different types of candidiasis?
Mucocutaneous
Chronic mucocutaneous (in those who can’t clear pathogen)
Systemic
Give 2 examples of agents responsible for cryptococcosis. Which of these are opportunistic?
C. neoformans
C. gattii (not necessarily opportunistic)
What are 1 of the defining features of a mycetoma?
Sulphur granules
What diseases are caused by cryptococcosis?
Pulmonary infection (usually mild) Meningitis (in immunocompromised, unless C. gattii)
Give an example of a toxic fungi
Aspergillus
List 3 presentations of aspergillosis
Saprophytic (fungus ball)
Allergic
Systemic
When does systemic candidiasis usually occur? What happens with a systemic infection?
With immunodeficiency (e.g. in neonates or HIV patients) Causes sepsis, can be fatal
What is pseudohyphae?
Hyphae without septa
Give an example of an organism that produce pseudohyphae
C. albicans
Give an example of a fungal AIDS-defining illness
Cryptococcal (fungal) meningitis
Does cryptococcus have a capsule?
Yes
What type of fungi is aspergillus?
Filamentous
What type of fungi is cryptococcus?
Yeast
What type of fungi is candida?
Yeast
How are fungal infections diagnosed?
Microscopy Culture Ag detection PCR (pan-fungal if not sure if fungal infection) Other (e.g. mass spectrometry)
List 4 systemic drugs used in anti-fungal chemotherapy. Give an example of each
Polyenes (e.g. amphotericin B)
Triazoles (e.g. fluconazole, voriconazole)
Echinocandins (e.g. capsofungin)
5-fluorocytosine
How can fungi be distinguished?
By conidia (have to grow under special conditions)
What is an India ink stain?
Negative stain
How can skin be viewed with microscopy?
Normally opaque under microscope; keratin must be dissolved
What is the characteristic microscopic feature of epidermophyton?
Distinctive appearance of macroconidia
What is the “quick and dirty” test for C. albicans?
Germ tubes; make pseudohyphae in the lab (usually in horse serum)
What diagnostic method is often used for cryptococcus?
Ag detection (detect capsular Ag in CSF, can be used to monitor treatment)
What is the drawback of amphotericin B?
Very toxic
List 2 classes of topical anti-fungal chemotherapeutic agents and give examples of each
Polyenes (e.g. nystatin)
Imidazoles (e.g. clotrimazole)
What are the 2 main targets of anti-fungals?
Ergosterol
Nucleic acids
What is ergosterol?
Sterol found specifically in fungal cytoplasmic membranes
What do polyenes act on?
Bind to ergosterol to disrupt integrity of fungal cell membrane
What is the mechanism of action of allylamines, triazoles and morpholines?
Affect synthesis of ergosterol
Why are polyenes so toxic?
Also bind to cholesterol and disrupt host cell membranes
How are polyenes usually administered?
IV
What is the mechanism of action of 5-flurocytosine?
Prodrug that is metabolised to 5-flurouracil in the body
Affects DNA and RNA synthesis
How is 5-flurocytosine selectively for fungi?
Only fungi have cytosine deaminase to activate the drug
What is the drawback of 5-flurocytosine?
Resistance occurs readily
What drug is usually used to treat Candida spp.?
Fluconazole
What drugs are usually used to treat cryptococcus?
Amphotericin B + 5-flurocytosine
What drug is usually used to treat Aspergillus?
Voriconazole
What drug is usually used to treat dimorphic fungi?
Amphotericin B
What topical agents are usually used to treat dermatophytes?
Terbinafine (“Lamisil)
Clotrimazole (“Canesten”)
Amorolfine (“Loceryl”
What orally administered agents are usually used to treat dermatophytes?
Terbinafine
Fluconazole
Griseofulvin (most toxic)
When are orally administered agents used to treat dermatophytes?
When infection is difficult to treat topically or is widely disseminated on the skin
Also if in nails (grows slowly, have to treat topically for a long time - oral treatment may be preferred to somewhat reduce treatment time)
