15 - Medical Mycology

Question 1

Define mycology? What are mycoses?

Answer 1

The study of fungi.

Mycoses are fungal infections.

Question 2

What fungal species is on the list of top 8 hospital acquired infections? What is the numb er of isolates, percentage, and crude mortality %?

Answer 2

The candida species

934 isolates, 7.6%, and 40% crude mortality.

Question 3

What are some general characteristics of fungi?

Answer 3

They are eukaryotic microbes:

• membrane bound
• ER
• mitochondria
• golgi
• lysosomes
• LINEAR chromosomes

Question 4

What do fungal membranes contain instead of cholesterol? What drugs can target this?

Answer 4

Ergosterol.

Can be targeted with antifungal called Amphotericin B that binds ergosterol.

Azole and allylamine drugs interfere with ergosterol biosynthesis.

Question 5

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?

Answer 5

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.

Question 6

The majority of fungi are ____ _____. What are the exceptions?

Answer 6

Free-living.

Candida albicans and malassezia furfur which are a natural component of the human flora.

Question 7

Fungi are heterotrophic, what does this mean? What does saprobe/saprophyte mean?

Answer 7

Heterotrophic: they get their nutrients from organic matter.

Saprobe/saprophyte: organism living on dead organic matter

Question 8

Most fungi are non-____?

Answer 8

Non-motile

And can really only move by changes in air current.

Question 9

What are characteristics of yeast?

Answer 9

unicellular, spherical or ellipsoidal.

Reproduce by budding or fission.

Some elongate and adhere to one another to form pseudomycelium/pseudohyphae.

Question 10

What are the types of pathogenic yeast?

Answer 10

Cryptococcus neoformans-exist only as yeast

Histoplasma capsulatum is dimorphic.

Question 11

What does it mean if yeast is dimorphic?

Answer 11

That the yeast changes morphology based on the temperature of the room such as yeast to hyphae.

Question 12

What is hyphae/mycelium?

Answer 12

Mold.

Hyphae are branching cylindrical tubules that can be:

• nonseptate: coenocytic (multiple nuclei)
• septate: uninucleate or multinucleate (coenocytic)

Question 13

What is the general life cycle of fungi?

Answer 13

1. Asexual spores are haploid (1N), and many but not all have a stable diploid form as well.
2. 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.

Question 14

What happens with a diploid organism when there’s no carbon source present?

Answer 14

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.

Question 15

It is more advantageous for a fungal organism to be ____?

Answer 15

Diploid; this is because they can handle DNA damage due to having two copies whereas haploids can’t handle much DNA damage.

Question 16

What are blastoconidia?

Answer 16

One cell budding off from another.

These are vegetative, not dormant, and will keep dividing.

Question 17

What are chlamydoconidia?

Answer 17

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.

Question 18

What are arthroconidia?

Answer 18

Single-celled conidia that form by the disjoining of hyphal cells.

They look like little rectangles coming off of a tube.

Question 19

What are conidiospores? What are the two types?

Answer 19

Spores that are borne naked on specialized structures.

1. Macroconidia are large multi-celled conidia that look almond shaped with horizontal lines across them.
2. Microconidia are small single-celled conidia that look like pearl chains on a stalk

Question 20

What are sporangiospores?

Answer 20

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.

Question 21

What are mycotoxins (mycotoxicoses)? What is this usually a result of?

Answer 21

Poisonous secondary metabolites produced by fungi.

Usually a result of ingesting contaminated food.

Question 22

What can result from ingestion of mushrooms of the Amanita species?

Answer 22

Severe or fatal liver and kidney damage by alpha-amantinin inhibiting RNA polymerase II.

Question 23

What is aflatoxin?

Answer 23

A mycotoxin produced by Aspergillus flavus and is mutagenic/carcinogenic and is often a contaminant of peanuts, corn, grains, and other food.

Question 24

What is the most potent natural carcinogen known?

Answer 24

Aflatoxin B1.

It’s thought to lead to liver cancer.

Question 25

What are ergot alkaloids?

Answer 25

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.

Question 26

What are some other mycotoxins?

Answer 26

Citrinin, fumonisins, ochratoxin, and trichothecenes.

Question 27

How are mycological infections diagnosed?

Answer 27

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.

Question 28

Other than microscopy, how can fungal infections be diagnosed?

Answer 28

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).

Question 29

Most of our understanding about resistance to antifungal agents comes from observations of _____ as well as other species of _____.

Answer 29

C. albicans

Candida

Question 30

For opportunistic fungal pathogens other than C. albicans, what do we know about antifungal resistance?

Answer 30

There’s virtually no info for the mechanism of antifungal resistance, and fungi apparently do not destroy or modify antifungal drugs.

Question 31

Resistance to antifungal drugs can occur through what?

Answer 31

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.

Question 32

What are primary and secondary resistance to antifungal drugs?

Answer 32

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

Question 33

Resistance to antifungal drugs usually develops slowly from the emergence of what?

Answer 33

Intrinsically resistant organisms or through gradual changes in cellular structures or functions from previous exposure to the drug

Question 34

What is the eagle effect?

Answer 34

Emerging with fungi.

An organism that is resistant to high concentrations of the drug (echinocandins) but susceptible to low concentrations.