Mycology Flashcards
Characteristics of Fungi
- Eukaryote
- Cell wall made of chitin
- Heterotrophy
- Unicellular
- Asexual and Sexual reproduction
Main groups of fungi
1.Zoosporic fungi
2. Zygomycetous fungi
3. Dikarya
What’s a zoosporic fungi
It’s a primitive aquatic fungi who can be a saprotroph, a symbiont and a parasite. It is a rhizoid structure which can make it Anchored and it spreads via zoospores
What is a Zygomycetous fungi ?
It’s a fungi that was able to adapt to life on land. This fungi is aseptated filamentous fungi and spread via zygospores and sporangiospores
Dikarya Kingdom? Composed of which groups and what are their characteristics?
- Ascomycota
- They live as septated filamentous fungi OR yeast and spread via ascospores and conidia
- Basidiomycota
- They live as septated filamentous fungi OR yeast and spread via basidiospores (sexually produced fungal spore carried by a basidium)
The role of Fungi
Biodegradation
Meaning of being Eukaryote
Fungi have a true nucleus, a protein secretion pathway, a vacuole, a mitochondrion and a cytoplasmic membrane
Characteristics of Chitin
- it is the exoskeleton of fungal cells
- Roles: Structure, Protection, exchanges (interaction with environment)
- Made of polysaccharides
Definition of heterotrophy and the steps of fungi
Heterotrophy means that the fungi cannot make its own nutrient.
Steps:
1. The fungi will secrete an enzyme that will degrade everything around them
2. Once this step done, the fungi will absorb everything to get nutrients
It has a direct impact on their lifestyle
Different lifestyle of fungi and their characteristics
Saprothroph: Organism that feeds on non-living matter
Symbiont: It lives in harmony with another organism
Parasite: will invade another living organisms to survive
Predators: will actively trap or kill other living organisms to survive
Note: Fungi can switch from one lifestyle to another for their survival
Unicellular characteristics
Yeast
- Will reproduce through Budding or fission and grow as independant cells
Molds
- grow as multinucleated tubes (with or without septae)
- Hyphae can contain septa
- Mycelium : ensemble of hyphae
- Fruiting body Top part of the mushroom and can be use to grow spores in lab
Asexual and Sexual reproduction
Sexuality is fluid in fungi
Asexual- Anomorph: Forms conidia, no partner, mitosis
Sexual: use meiosis- reproduction with mating type
two groups: Heterothallic and Homothallic
Forms Ascopores and can change sex
Parasexual
Dispersal techniques of fungi using animal
Attracting animals
- Attract animals by producing sticky spores which stick to the animals and spread it elsewhere
Controlling animals
Dispersal techniques using the wind and the fungi associated
Mastering the wind (basidiomycetes)
Going with the wind (ascomycetes)
Shooting (Zygomycete)
Type of ascocarp
- Apothecium
- Perithecium
- Cleistothecium
formation of basidiospores
- Germination
- formation of Mycelia. Two mating types (+ and -)
- Plasmogamy
- Fusion between + and - mating types= Formation of dikaryotic mycelium
- Mitosis
- Under right conditions, Basidiocarp is formed
- Gills of basidiocarp contain cells called basidia
- Karyogamy
- Basidia form diploid nuclei (zygote (2n) formation)
- Meiosis
- Four haploid nuclei are formed in the basidium (1n)
- Cell division
- Four basidiospores (n) are formed
- Dispersal
Formation of ascospores
- Plasmogamy and mitosis
- Ascogonium and Antheridium fuse
- Mitosis+cell division= formation of dikaryotic hyphae
- Dikaryotic hyphae = Formation of fruiting body named Ascocarp
- Karyogamy
- Nuclei in asci fuse to form diploid zygote (2n)
- Meiosis
- Ascus with four nuclei is formed
- Mitosis and cell division
- Eight haploid ascospores are formed
- Dispersal and germination
Life cycle of Zygomycete
- Germination
- Formation of Mycelia
- Two mating types (+ and -) are in close proximity
- Formation of extensions called Gametangia forms between them
- Formation of Mycelia
- Plasmogamy
- Fusion of the mating types= Zygosporangium with multiple haploid nuclei
- Zygosporangium forms a thick protective coat
- Karyogamy
- The nuclei fuse to form multiple diploid nuclei
- Meiosis and germination
- a sporangium grows on a short stalk, haploid spores are formed inside the sporangium
Two groups of fungal infections
- superficial infections
- invasive infections
Characteristics of superficial infections
- Most common infection and often benign
- Frequent in immunocompetent
- Provoked by dermatophytes (Tinea)- feed on keratin
- Tinea unguium
- 5-10% population
- Difficult to eradicate
- 3-6 months oral antifungals
- Tinea pedis
- Commonest fungal infection of humans
- Up to 70% of all Tinea
- Topical antifungal therapy for 10-14d
- Recurrence common
- Tinea unguium
- Environmental origin: Anthropophile, Zoophile or Geophile
- Can be cause by Candida albicans infections
- Human commensal organism
- Morphological switch is required for virulence, and not completely understood today
- Can cause the mouth, the skin and the reproductive areas
Characteristics of invasive infections
- Rare and lethal if untreated
- mostly in immunocompromising patients
- Clinical classification
Groups in invasive infections and their characteristics
- Yeasts
- Systemic disease, pulmonary absent or subclinical
- Candidemia
- C.albicans yeast reach the blood flow and access different organs
- Average mortality rate: 20-50%
- Average stay at the hospital; 2-8 weeks
- Cryptococcus
- Basidiomycota
- Encapsulated yeast
- Two common sp.: C. neoformans and C. gattii
- Environnement : Soil, Eucalyptus trees, Bird droppings
- Cryptococcosis
- acquired by breathing yeasts or spores
- Immunocompromised and immunocompetent at risk
- pulmonary infections (cryptococcomas):
- Often misdiagnosed
- Asymptomatic in 25 to 50% of cases
- All patients with this diagnosis needs to have a CSF puncture can lead to Cryptococcal meningitis
- Cryptococcal meningitis
- In HIV positive patients: 80% CSF culture are positive for Cryptococcus
- Treatment in 3 phases:
- Induction- 1 week under amphotericin
- Consolidation- high dose of fluconazole
- Maintenance - Low dose of fluconazole for a year
- cryptococcosis overall mortality rate is above 50%, with a death estimate of 625,000/year.
- Cryptococcus gatti
- Over 300 human and over 400 animal cases
- Appeared in 1999
- Pneumonia and meningitis in immunocompetent patients
- Infecting native trees and soil
- Molds
- primary pulmonary disease with dissemination less common
- Majority of them are opportunistic, very aggressive and destructive
- Aspergillus most common (>80%)
- Aspergillus most common species (Ascomycota)
- Disease: Invasive Pulmonary Aspergillosis
- Others
- Rhizopus, Absidia, Mucor (Zygomycetes)
- Penicillium
- Pseudallescheria
Why making antifungal is a challenge ?
- Fungi are eukaryote like us, humans
- But they have a CHITIN based wall which is the SOLUTION
- The wall is made of ergosterol (which is different from us)
Targets of antifungals and their characteristics
- Fungal cell wall
- Incredibly diverse polysaccharide structures all based on chitin
- But the amount on information on chitin is limited bc it is mostly present in plants and fishes
- So we target something else
- Echinocandins-Cell wall inhibitors
- Inhibition of B-glucans
- Newest family of molecules approved by the FDA (2001)
- First line of defense against yeast invasive infections → Fungicidal effect on most of them meaning they kill them
- Fungistatic in molds meaning that they stop the growth
- Echinocandins-Cell wall inhibitors
- Ergosterol
- Ergosterol insure fungal plasma membrane fluidity
- 2 main families of antifungals targets this molecule:
- Polyenes- Ergosterol binder
- Isolates in the 50’s and are still the antifungal gold standard- bread spectrum activity and low fungal resistance
- Use in severe cases of invasives infections since it has massive consequences on us
- Important toxicity- this is due to the structures of Cholesterol and Ergosterol being similar + the drug kill everything
- Azoles- Inhibitor of ergosterol synthesis
- Synthetic family of molecules developed since the 60’s containing:
- Imidazole group
- Triazole group
- First line of defense against invasive mold infections as generally fungicidal
- Generally fungistatic against yeast
- Synthetic family of molecules developed since the 60’s containing:
- Polyenes- Ergosterol binder
