Mycology Flashcards
Lectures: -Week 1, day 2, lecture 7 - Fungal biology -Week 1, day 2, lecture 8 - Medical mycology
What is the ‘mycelium’?
Mass of branching hyphae which make up the vegetative growth of the fungus
What are hyphae?
Fungal filaments
Which types of hyphae are there? (2)
- Septate hyphae
- Coenocytic hyphae
True or false: nucleae cannot pass septae in the septate hyphae
False; nulcei can pass the septal pores
Fungal grwoth follows a growing tip. Which structure is located there, that allows fungal growth?
The spitzenkörper, a cluster of enzymes rquired for growth
There are more varieties of [yeasts/molds]
Molds (400.000 known species, whereas there are ~1.500 known yeast species)
What are the main differences between yeasts and molds? (3)
- Colony shape -> molds have fluffy colonies, whereas yeasts have round colonies
- Structural makeup -> molds are multicellular, yeasts are unicellular
- Reproduction -> molds can perform both sexual and asexual reproduction. Yeasts reproduce asexually by budding.
What are dimorphic fungi?
Fungi that can grow/act as both yeasts and molds, depending on the environment
What component is (almost) always present in fungal cell walls?
Chitin (and often also β-glucan)
In what way do fungal cell membranes differ from mammalian membranes? Which (therepeutic) advantage does this offer?
Contain ergesterol (instead of cholesterol), which can be used to targed fungal cell membranes without disrupting human cells
Fungi are heterotrophs. What does this mean?
Fungi cannot acquire energy from the sun -> they need to absorb nutrition from their surroundings
How do fungi absorb nutrients from their surroundings?
They secrete enzymes that digest a substrate in their surrounding, after which they absorb the nutrients
Fungi can produce both sexually and asexually. When do they choose sexual reproduction, and when asexual reproduction?
Asexual reproduction is performed in a nutrient-rich environment that does not require a different genetic makeup to survive
Sexual reproduction is performed under stress conditions -> different genetic makeup can increase survival
True or false: most of the fungal life cycle is diploid
False; most of the fungal life cycle is haploid, only after karyogamy there is a diploid stage
What are the steps in asexual reproduction of fungi? (3)
- Mycelium ->
- Spore-producing structures produce spores ->
- Germination
What are the steps in sexual reproduction of fungi? (6)
- Mycelium ->
- Plasmogamy = fusion of cytoplasm with another fungus ->
- Heterokaryotic stage ->
- Karyogamy = fusion of nuclei, producing a diploid zygote ->
- Meiosis, producting haploid spores ->
- Germination
Where do spore producing structures form in fungi?
At the end of hyphael tips
True or false: in fungal sexual reproduction, a ‘male’ and ‘female’ fungus can be distinguished
False, there is no clear distinction between the counterparts in fungal sexual reproduction. They are therefore referred to as ‘α and B)
How long kan the heterokaryotic stage, that occurs after the cytoplasm of the sexually reproducing fungi have fused, last?
Up to several years
Wat is the heterokaryon?
Union of two parent mycelia after nuclear fusion (diploid stage)
How do yeasts reproduce?
Yeasts reproduce via asexual reproduction by splitting their nucleus and budding
How many fungal phyla are there?
7
What are the 7 fungal phyla?
- Cryptomycetes
- Microsporidians
- Chytrids
- Zoopagomycetes
- Mucoromycetes
- Ascomycetes
- Basidomycetes
Into which three groups can fungal infections be subdivided, based on the loctation of infection?
- Cutaneous
- Subcutaneous
- Systemic
How are superficial cuteanous fungal infections defined? What are their characteristics? (3)
Cosmetic infections of the skin or hair shaft
- No living tissue invaded
- No cellular immune response
- No pathological changes ilicited
What are examples of superficial cutaneous fungal infections? (3)
- Piedra = asymptomatic infection of the hair shaft
- Malassezia yeats -> cause dandruff
- Tinea nigra = skin lesions with brown to black macules
How are cutaneous fungal infections defined? What are their characteristics? (3)
Non-living infections of skin, hair or nails
- No living tissues involved, restricted to keratinized layers
- May stimulate immune responses
- Pathological changes due to the presence of the fungi or their metabolic products
What are examples of cutaneous fungal infections? (3)
- Tinea = ringworm -> colonization of stratum corneum
- Onychomycosis (‘kalknagel’) -> depends on human host to complete life cycle
- Candidiasis (oral, vaginal, cutaneous, nails)
What are the three epidemiological groups of tinea/ringworm?
- Anthropophilic = live on human host
- Zoophilic = live on animal hosts, can incidentally infect humans
- Geophilic = live on keratin in soil
How are subcutaneous fungal infections defined?
Chronic, localized infections of the skin and subcutaneous tissue following the traumatic implantation of the aetiologic agent
What is implantation of a fungal infection by (minor) trauma called?
Implantation mycosis
What are examples of subcutaneous fungal infections? (3)
- Mycetoma
- Chromoblastomycosis
- Sporotrichosis
What is mycetoma?
Chronic, granulomatous infection of subcutaneous tissue, characterized by the formation of granules
True or false: mycetoma always has the same causative agent
False -> there are ~70 causative agens (some of which are bacterial)
What is chromoblastomycosis?
Chronic, granulomatous infection of subcutaneous tissue, characterized by the formation of sclerotic bodies
In which areas of the world is chromoblastomycosis most common?
Latin America and China
What is sporotrichosis?
Chronic infection of the cutaneous and subcutaneous tissue, characterized by nodular lesions. Caused by Sporothrix spp.
What are the main diagnostics of subcutaneous fungal infections?
- Fine-needle aspiration
- Deep-seeded biopsy
Into which groups can systemic fungal infections be divided?
- Dimorphic
- Systemic
What are dimorphic fungal infections?
Systemic fungal infections by fungal pathogens that can overcome the physiological and cellular defences of the human host by changing their morphological form (mycelium -> yeast)
What is the primary site of infection for dimporphic fungal infections?
Lung
What are the 5 diseases caused by dimorphic fungal infections?
- Blastomycosis
- Coccidiomycosis (BSL-3)
- Histoplasmosis (BSL-3)
- Paracoccidiomycosis
- Talaromyces mareffei infections
What is most often the clinical presentation of dimorphic fungal infections?
50-95% of patients has flu-like symptoms
(5% gets a disseminated infection)
Which types of diagnostics are used in the diagnosis of dimorphic fungal infections? (3)
- Rapid serology diagnostics
- Histology
- Culturing
What are opportunistic fungal infections?
Systemic fungal infections by cosmopolitan fungi with low inherent virulence, which occur in debilitated patiens whose normal immune defence mechanisms are impaired
What are examples of opportunistic fungal infections? (5)
- Candidiasis
- Cryptococcosis (pulmonary of meningeal)
- Aspergillosis
- Scedosporiosis
- Zygomycosis
What is special about aspergillosis that can lead to a very varied disease presentation?
The immune status determines the disease presentation -> a hyperactive immune system results in allergic/asthmatic reactions, whereas a weakened immune system allows for (necrotizing) aspergillomas and dissemination
What is scedosporiosis?
Spectrum of diseases caused by Scerosprium and Lomentospora species
What is zygomycosis?
Disease caused by infection by Mucormyctes
What are the diagnostics of opportunistic fungal infections? (3)
- Culturing
- Molecular diagnostics
- Galactomannan test
What is the problem with culturing opportunistic fungal infections?
Samples can be contaminated by cosmopolitan agents -> inability to determine whether these are causative agents or contamination
Result: culturing only possible from sterile areas
What is the galactomannan test?
Serological test for metabolic products of fungal infection
