15 - Medical Mycology Flashcards
Define mycology? What are mycoses?
The study of fungi.
Mycoses are fungal infections.
What fungal species is on the list of top 8 hospital acquired infections? What is the numb er of isolates, percentage, and crude mortality %?
The candida species
934 isolates, 7.6%, and 40% crude mortality.
What are some general characteristics of fungi?
They are eukaryotic microbes:
- membrane bound
- ER
- mitochondria
- golgi
- lysosomes
- LINEAR chromosomes
What do fungal membranes contain instead of cholesterol? What drugs can target this?
Ergosterol.
Can be targeted with antifungal called Amphotericin B that binds ergosterol.
Azole and allylamine drugs interfere with ergosterol biosynthesis.
Other than ergosterol in their membranes, what other characteristic of fungi can be targeted by drugs because it differs from humans? What drug can target this?
Fungal cells have a rigid cell wall made of:
- chitin, alpha-glucan, B-glucan, and alpha-mannan
- mannoproteins
Echinocandins are a class of drugs that inhibits B-glucan synthesis.
The majority of fungi are ____ _____. What are the exceptions?
Free-living.
Candida albicans and malassezia furfur which are a natural component of the human flora.
Fungi are heterotrophic, what does this mean? What does saprobe/saprophyte mean?
Heterotrophic: they get their nutrients from organic matter.
Saprobe/saprophyte: organism living on dead organic matter
Most fungi are non-____?
Non-motile
And can really only move by changes in air current.
What are characteristics of yeast?
unicellular, spherical or ellipsoidal.
Reproduce by budding or fission.
Some elongate and adhere to one another to form pseudomycelium/pseudohyphae.
What are the types of pathogenic yeast?
Cryptococcus neoformans-exist only as yeast
Histoplasma capsulatum is dimorphic.
What does it mean if yeast is dimorphic?
That the yeast changes morphology based on the temperature of the room such as yeast to hyphae.
What is hyphae/mycelium?
Mold.
Hyphae are branching cylindrical tubules that can be:
- nonseptate: coenocytic (multiple nuclei)
- septate: uninucleate or multinucleate (coenocytic)
What is the general life cycle of fungi?
- Asexual spores are haploid (1N), and many but not all have a stable diploid form as well.
- When two opposite mating types come in contact and form a diploid organism, they can divide and reproduce through mitosis to make more diploid (2N) cells.
What happens with a diploid organism when there’s no carbon source present?
It goes through meiosis to make meiotic 1N haploid progency.
Those haploid organisms can produce new haploid organisms that can grow and be happy as haploid until they meet another haploid organism of the opposite mating type.
It is more advantageous for a fungal organism to be ____?
Diploid; this is because they can handle DNA damage due to having two copies whereas haploids can’t handle much DNA damage.
What are blastoconidia?
One cell budding off from another.
These are vegetative, not dormant, and will keep dividing.
What are chlamydoconidia?
Thick-walled single cell spores that are resistant to adverse conditions.
These are dormant until wind or something moves them to an environment that’s conducive to germination.
What are arthroconidia?
Single-celled conidia that form by the disjoining of hyphal cells.
They look like little rectangles coming off of a tube.
What are conidiospores? What are the two types?
Spores that are borne naked on specialized structures.
- Macroconidia are large multi-celled conidia that look almond shaped with horizontal lines across them.
- Microconidia are small single-celled conidia that look like pearl chains on a stalk
What are sporangiospores?
Single-celled haploid spores that are formed within sacs -that look like a gumball machine- called sporangia from the end of a special hyphae.
These sacs burst to release spores, and inhalation of these can lead to the production of a haploid organism.
What are mycotoxins (mycotoxicoses)? What is this usually a result of?
Poisonous secondary metabolites produced by fungi.
Usually a result of ingesting contaminated food.
What can result from ingestion of mushrooms of the Amanita species?
Severe or fatal liver and kidney damage by alpha-amantinin inhibiting RNA polymerase II.
What is aflatoxin?
A mycotoxin produced by Aspergillus flavus and is mutagenic/carcinogenic and is often a contaminant of peanuts, corn, grains, and other food.
What is the most potent natural carcinogen known?
Aflatoxin B1.
It’s thought to lead to liver cancer.
What are ergot alkaloids?
A mycotoxin.
Family of related compounds produced by the genus Claviceps that can lead to gangrene, nervous spasms, dilusions, muscle contractions, vessel constriction and convulsions.
What are some other mycotoxins?
Citrinin, fumonisins, ochratoxin, and trichothecenes.
How are mycological infections diagnosed?
KOH-technique for direct microscopic examination of structural characteristics of fungi grown in culture.
Cultivation on blood agar at 37 degrees, sabouraud’s agar, and on other special media.
Other than microscopy, how can fungal infections be diagnosed?
Serological method tests to detect antibodies against fungal antigens or fungal antigens in the patients serum.
PCR
Fleurescent in situ hybridization (FISH)
Mass Spectrometry (way of the future-amino acid sequence gives you a finger print of the organism causing the illness).
Most of our understanding about resistance to antifungal agents comes from observations of _____ as well as other species of _____.
C. albicans
Candida
For opportunistic fungal pathogens other than C. albicans, what do we know about antifungal resistance?
There’s virtually no info for the mechanism of antifungal resistance, and fungi apparently do not destroy or modify antifungal drugs.
Resistance to antifungal drugs can occur through what?
Efflux pumps that target alterations and reduced access to drug targets (ie organisms take the drug out of the cell through efflux).
Antifungal resistance genes are NOT transferred horizontally from cell-to-cell by the mechanism used by bacteria. They can however pass it to their progeny.
What are primary and secondary resistance to antifungal drugs?
primary: an organism thats resistant to a particular drug without prior exposure
secondary: an organism that develops resistance to a particular drug only after exposure to the drug
Resistance to antifungal drugs usually develops slowly from the emergence of what?
Intrinsically resistant organisms or through gradual changes in cellular structures or functions from previous exposure to the drug
What is the eagle effect?
Emerging with fungi.
An organism that is resistant to high concentrations of the drug (echinocandins) but susceptible to low concentrations.
