Fungi Flashcards
The study of fungi is called ____?
Disease caused by fungi are called _____?
Study of fungi = mycology
Diseases caused by fungi = mycoses
Of more than 100,000 fungal species, only _____ have pathogenic potential for humans, only _____ account for clinically important infections
Only 100 have pathogenic potential for humans
Only a FEW account for clinically important infections
List 4 general features of fungi
- Prokaryotic or Eukaryotic?
- Cell wall, cell membrane, both?
- Autotrophs or heterotrophs?
- Anaerobic or aerobic respiration?
- Eukaryotic (have nucleus w/ nuclear membrane and membrane-bound organelles)
- Cell wall and Cell membrane
- Heterotrophs
- Respire aerobically
Fungi cell membrane contains ______
Fungi cell wall contains ______
Cell membrane: contains ergosterol (rather than cholesterol found in mammalian cells)
Cell wall: composed mainly of chitin (rather than peptidoglycans like bacteria…. so, unaffected by antibiotics)
Antifungal Agents = Antimycotic
Note: the fungal cell wall and plasma membrane are critical for cell viability and pathogenicity
-NO place for antibiotics (they will NOT work)
4 Examples of Antifungal Agents
- Echinocandins - inhibit enzyme that synthesizes B-glucans
- Polyenes - bind ergosterol, weaken membrane, lead to PORE formation
- Azoles - inhibit enzyme that synthesizes ergosterol
- Allylamines - inhibit enzyme that synthesizes ergosterol
Which antifungal(s) target the cell wall? Which target the cell membrane?
Cell wall - echinocandins
Cell membrane = polyenes, azoles, allylamines
Explain what is meant by fungi being “heterotrophs”
They acquire nutrients by absorption
They are extracellular digesters of food & nutrient absorbers
– They secrete hydrolytic enzymes and acids into the surroundings to decompose complex molecules into simpler ones that can be absorbed
Heterotrophic fungi are specialized into 3 main types:
- Saprobes
- Parasitic Fungi
- Mutalistic Fungi
- Saprobes: absorb nutrients from dead organic material
- Parasitic Fungi: absorb nutrients from cells of living hosts, some are pathogenic
- Mutalistic Fungi: absorb nutrients from a host but reciprocate to benefit the host
Types of Pathogenic Fungi: Morphological Classification
- Filamentous Molds
- Yeast
- Dimorphic
Filamentous Molds
Multicellular Branching filaments (hyphae) which may be septate or non-septate
Mycelium- mass of connected hyphae (complex of hyphae), grows through and digests its substrate
Reproduce via asexual spores
Most are dispersed by wind
Sporulation
Fungal spores are metabolically dormant, protected cells, released by the mycelium in enormous numbers
Spores can withstand drying out b/c of their waterproof outer layer
When a spore lands on an appropriate food source, it germinates (starts to grow) and establish new colonies
Borne by the air or water to new sites where they won’t have to compete for food
Spores contain identical genetic material to the original fungi
Yeasts
UNIcellular!
Oval or round cells
Asexual budding = reproduction
May form pseudohyphae as Candida and Cryotococcus neoformans
Dimorphic Fungi
Ability to SWITCH between two morphologies
- Fungi able to conver from hyphal to yeast
- Can be subdivided into thermal (morphologic switch induced by temperature) and non-thermal dimorphic fungi (included by example by oxygen carbon dioxide concentration)
How does the morphologic switch to fungi impact pathogenesis?
The morphologic switch is essential for the pathogenesis of dimorphic fungi
For mammalian fungi, the transition to a yeast or yeast-like growth results in altered cell wall composition, as well as production of proteins to evade immune defenses or toxins to alter host behaviour
Pathogenic Fungi – true pathogens vs. opportunistic pathogens
True Pathogens: have the ability to invade & cause disease
Opportunistic Pathogens: normal -> will not cause harm… other conditions -> decreased immunity, will cause injury & infection
Clinical Classification of Fungi
Superficial Mycoes
Cutaneous Mycoses
Subcutaneous Mycoses
Deep – Endemic Mycoses, Opportunistic Mycoses
- Superficial Mycoses
Confined to superficial layers of the skin
No tissue invasion
- Cutaneous Mycoses
Involve the skin, nail or hair with tissue destruction and immunological reaction
- Subcutaneous Mycoses
Sporotrichosis (“rose gardener’s disease”) , a rare infection caused by a fungus called Sporothrix
- Deep Systemic: Endemic Mycoses
Primary pulmonary lesions that may disseminate to any organ, mainly in immunocompromised patients
They are caused by dimorphic infections (inhalation of spores)
- Deep Systemic: Opportunistic Mycoses
RARE in normal individual, but affect the immunocompromised as with:
-Organ transplantation, post chemotherapy for cancer, immunodeficient due to AIDS
EX: systemic candidaisis, crytococcosis, apergillosis, pneumocystitis jirovecii
Endemic vs. Opportunistic Fungi
- Geographical
- Portal of Entry
- Host
- Recovery
Endemic
- Environmental
- Lungs
- Immunocompetent and immunocompromised
- GOOD prognosis
Opportunistic
- Normal flora/environmental
- Variable
- ImmunoCOMPROMISED
- POOR prognosis
Transmission of fungal infections
Depends on infectious agent (fungus) & type of infection
Ex: touch = skin & mucous membrane infections; inhalation = lung infections (deep seated mycoses)
Laboratory identification
Depends on infectious agent (fungus) and/or type of infection
Specimens: skin scrapings, swabs, nail clippings, blood, pus, CSF, sputum, tissue biopsies, bronchoscopy washings
1) Microscopy
2) Cultures
3) PCR
4) Serology Antigen Testing (blood)
Management of Fungal Infections
Depends on infectious agent (fungus) and/or type of infection
Some such as superficial skin infections require topical therapy, only with cream
Some require local therapy
Some require oral therapy for skin & nail infections, up to 1 year
In the immunocompromised – systemic therapy is required
