Intro to Mycology Flashcards
General characteristics of fungi
- aerobic
- non-photosynthetic (lack chlorophyll)
- grow well at room temperature
- prefer dark, moist environments
Do fungi have a true cell wall?
Yes, contains cellulose and chitin
- carb polymers (glucans, mannans) = 50-60% of cell wall
- 5-10% protein
Are antibiotics that attack the cell wall useful against fungi?
No!
- are eukaryotes with nuclei, membranes, and ribosomes resembling mammals
- chemotherapeutics against fungi may damage the host
What do fungi cell walls contain instead of cholesterol?
Ergosterol
- common in mammalian membranes or phosphoglycerides
- helps define apical and basal aspect of cells (helps with cell orientation)
Saprophytes
Associated with soil or parasites of plants
How do fungi infect animals?
Chance occurrence due to inhalation, ingestion, penetration of wounds
Are fungal infections contagious?
Rarely, other than ringworm
What is the important of sexual stages?
Only important in establishing taxonomy and classification of individual fungi
What is important in identifying fungal isolates?
Asexual structures (conidia)
Dimorphic
Exist as both yeasts and hyphae
Yeast
Single celled eukaryotic form
- multiply asexually via budding
Hyphae
Mutlicellular with a thick cell wall
- long branching filaments
- bear conidia
Mycelium
Mass of hyphae
- single multicellular life form (aka: colony, thallus)
Septate
If the hyphae contain crosswalls
Aseptate
If the hyphae do not contain crosswalls
- aka: coenocytic
Thermal dimorph
A yeast at 37 C or in animal tissues (aka: parasitic phase) and is a mycelium at room temperature (aka: environmental, or filamentous phase)
- conversion from one to the other is due to a change in temperature, NOT a change in host!
Tissue dimporhs
Fungi that convert from mycelial phase to yeast phase due to factors in animal tissue
- phase conversion is not related to temperature, is only accomplished in the lab with artificial media
Conidia
Cells that are the product of asexual multiplication
- functionally similar to seeds of higher plants
- are not as resistant as bacterial endospores
Sporangium
Sac like structure that some conidia are born in
Macro versus microconidia
- macro: large and multicellular
- micro: small and one celled
Conidia produced as buds from hyphal parent
Microconidia
Arthroconidia
When hyphal cells form conidia and fragment
What are the 4 major subdivisions of fungi?
- zygomycota
- ascomycota
- chytridiomycota
- basidiomycota
Deuteromycota
Fungi without a known perfect state
- may represent asexual stages (anamorphs) of either Basidiomycota or Ascomycota
Mycophycomycota
Mychorhyzial fungi that have mutualism with tree roots
- truffles
Which class is known as the bread or pin molds?
Zygomycetes
- fast growing, terrestrial, saprobic
- non motile cells
- identification based on sporangial morphology
Entomophthoromycosis
Entomophthorales subcutaneous zygomycosis
- Conidiobolus and Basidiobolus
- occurs in horses
Mucormycosis
Mucorales, subcutaneous and systemic zygomycosis
- Rhizopus, Mucor, Rhizomucor, Absidia, Cunninghamella, Mortierella, Saksenaea, Apophysomyces
= mycotic ruminitis/placentitis –> grows on mucosal surfaces, ends with abortion or ruminitis
Which classification is known as mushrooms and toadstools?
Basidiomycetes
- saprobes and parasites
- dolipores allow cytoplasmic migration
- main concern with toxicities
Filobasidiella
Teleomorphs of known pathogenicity
Basidiomycosis
Coprinus and Schizophyllium
Mushroom poisoning
Aminita, Lepiotia, Coprinus, Psilocybe
What is the common mold?
Ascomycetes
- saprobes, parasites, lichen forming
- no current classes, have been grouped on how asci were arranged
- most pathogens!
Medically important Ascomycetes
Teleomorphs of known pathogenic fungi:
- Arthroderma
- Nannizzia
- Ajellomyces
- Pseudallescheria
- Eurotium
Agents of mycetoma
Leptosphaeria and Neotestudina
Black piedra
Piedraia hortae
What are known as conidial molds?
Hyphomycetes
- class of mycelial moulds, mostly comprised of Ascomycetes
- no sexual state is present
Dermatiaceous hyphomycetes
Produce dark brown, green-black, or black colonies
- causative agents of phaeohyphomycosis
Hyaline hyphomycetes
Are not darkly pigmented, colonies may be colorless or brightly colored
- agents of hyalohyphomycosis, aspergillosis, dermatophytosis, and dimorphic pathogens (Histoplasma capsulatum)
What is the only motile fungi?
Chytridiomycetes
- only causes disease in amphibians!
Epidermal changes due to _____ have been found in sick/dying adult anurans during mass mortality events associated with significant population declines
Chytridiomycete fungus
- associated with morbidity and mortality in wild and captive anurans from around the world
Cutaneous chytridiomycosis
Fatal disease of anurans
- proximate cause of recent amphibian declines
Chytridiales general characteristics
- waterborne
- pathogenic to adult amphibians, does not kill tadpoles but they are carriers
- prefers cooler temperatures
Chytridiomycosis pathogenesis
- hyperkeratosis
- sloughing and erosion of epidermis
- occasional ulcerations
Fungi that cause disease differ from taxonomically similar species by:
- surviving and growing at higher (body) temperatures
- growing in reduced oxidation-reduction environments of tissue
- overcome host defenses
The best example of transient adaptation to invasion and growth within tissue is _____
Dimorphic fungi
What are common fungal diseases that are non beneficial to either the host or the fungus?
- histoplasmosis
- blastomycosis
- coccidiomycosis
- sporotrichosis
Cryptococcus neoformans
One of the few fungi that produce capsules, except as a yeast
- when inhaled, it colonizes in nasal mucosa or can become inoculated into a wound –> produces a huge capsule and becomes a space occupying mass
Which species produces keratin and can establish equilibrium with some hosts?
Dermatophytoses
- specialized saprophytes that do not invade living tissue (feed only on dead cornified appendages)
- clinical disease is a toxic/allergic response to the presence of the organism and its metabolic byproducts
Which species gain entry into the body by traumatic implantation?
Subcutaneous mycoses
- limited invasive ability
What are some predisposing factors that may contribute to opportunistic fungal infection?
- prolonged administration of antibiotics
- administration of immunosuppressive agents or cytotoxic drugs
- immune deficiencies, cancer, diabetes, or recent surgery
Most fungal infections are chronic _______
Granulomas
- easily mistaken for tumors, bacterial disease, or non-infectious processes
What is the most useful tool for the diagnosis of fungal disease?
Appearance of the organism in tissue, aspirates, or exudates!!!
What is the only efficacious resistance to fungal infection?
Cellular defenses
- humoral antibodies play no role in fungal infections
Common points of entry for fungi
- lung (most common)
- skin
- gastrointestinal tract
Most fungi will grow within
Phagocytic cells
- are facultative intracellular organisms
- disseminate to other body parts via lymphatics and blood
With primary infection _____ immunity prevails, while with progressive disease development, _______ immunity plays a large role
Cellular; delayed hypersensitivity
What is one fungus in which the host response is minimal or nonexistent?
Cryptococcosis
