Mycology

Question 1

Mycology

Answer 1

The study of fungi

Question 2

Candida species
# isolates:
% of nosocomial bloodstream pathogens:
Crude mortality:

Answer 2

isolates: 934
% of nosocomial bloodstream pathogens: 7.6
Crude mortality: 40%

Question 3

Features of Eukaryotes

Answer 3

Membrane bound nucleus
Endoplasmic reticulum
Mitochondria
Golgi
Lysosomes
Linear chromosomes

Question 4

Difference between Fungi and higher Eukaryotic Cells

Answer 4

Fungal membranes contain ergosterol rather than cholesterol

Fungal cells are usually surrounded by a rigid cell wall composed of carbohydrate polymers and protein

Question 5

What drug binds ergosterol

What drugs interfere with ergosterol biosynthesis

Answer 5

Amphotericin B (polyenes)
Azole and Allylamine drugs interfere with biosynthesis

Question 6

Features of Fungi

Answer 6

Majority are free living in that they do not require a specific interaction with other live organisms
- Exceptions are Candida albicans and Malassezia furfur
Heterotrophic-nutrients are absorbed from organic matter - most fungi only require carbon and nitrogen source
Most fungi are nonmotile

Question 7

Yeast morphology

Answer 7

• Unicellular, spherical to ellipsoid (3-15 microns)
• Reproduce by budding or fission
• Yeast species identified by physiological tests and key morphological differences
• Some yeast elongate and adhere to one another forming pseudomycelium/pseudohyphae
• Pathogenic yeast (Cryptococcus neoformans exist only as yeast; Histoplasma capsulatum is dimorphic)

Question 8

Hyphae/Mycelium

Answer 8

Also referred to as mold
Hyphae: Branching cylindric tubules varying in diameter from 2-10 microns
Mycelium: Mass of intertwined hyphae that accumulate during active growth; pathogenic mold

Question 9

Types of hypahe

Answer 9

Nonseptate (Coenocytic - multiple nuclear divisions)
Septate
- Uninucleate cells
- Multinucleate cells (coenocytic)

Question 10

Rhizoids

Answer 10

Rootlike structures

Question 11

Asexual Reproductive Elements

Answer 11

1. Blastoconidia (budding)
2. Chlamydoconidia - thick walled single cells that are resistant to adverse conditions
3. Arthroconidia are single celled conidia that are formed by the disjoining of hyphal cells
4. Conidiospores are medically important spores that are borne naked on specialized structures
   - Macroconidia - Large, multicelled conidia
   - Microconidia - Small single celled conidia
5. Sporangiospores - single celled spores that are formed within sacs called sporangia from the end of a special hyphae

Question 12

General Fungal Infections

Answer 12

1. Can cause superficial, cutaneous, subcutaneous, systemic and opportunistic infections
2. Hypersensitivity to airborne conidia and/or spores leading to strong allergic reactions
3. Mycotoxins are poisonous secondary metabolites produced by fungi

Question 13

Mycotoxins

Answer 13

• Ingestion of mushrooms of Amanita species results in severe or fatal liver and kidney damage by α-amantin inhibiting RNA polymerase
• Aflatoxin produced by Aspergillus flavus is mutagenic/carcinogenic and is often a contaminant of peanuts, corn, grains and other food
• Ergot alkaloids are a family of related compounds that can lead to gangrene, nervous spasms, psychotic dillusions… (Discovery of LSD)

Question 14

Diagnostic Laboratory Procedures

Answer 14

• Direct microscopic examination of clinical specimen
• Cultivation on blood agar at 37°C, Sabrouraud’s agar and on other special culture media
• Microscopic examination of structural charactersitics of fungi grown in culture
• Serological methods
• PCR
• FISH
• Mass spec

Question 15

Targets of antifungal drugs

Answer 15

Ergosterol
Cell wall synthesis
Nucleic Acid synthesis
Disruption of microtubules

Question 16

Possible effective strategies for combination therapy

Answer 16

1. Inhibition of different stages of the same biochemical pathway
2. Increased penetration of one agent into the cell through a permeabilizing activity of another agent
3. Inhibition of the transport of one agent out of the cell by another agent
4. Stimulation inhibition of different fungal cell targets

Question 17

Possible Drawbacks to combination therapy

Answer 17

1. The action of one agent reduces the concentration of the target for the second agent
2. The action of one agent modifies the target for the second drug
3. The action of one agent blocks accessibility of the second agent for its target

Question 18

Most of our understanding of resistance to antifungal agents comes from observations of ________ and other species of ________

Answer 18

C. albicans; Candida

Question 19

Resistance to antifungal drugs can occur thorugh _____ _______, _______ _________ and ________________

Answer 19

Efflux Pumps; Target Alterations; Reduced Access to Drug Targets

Question 20

Primary resistance

Answer 20

An organism that is resistant to a particular drug without exposure to the drug

Question 21

Secondary Resistance

Answer 21

An organism that develops resistance to a particular drug only after exposure to the drug

Question 22

Eagle Effect

Answer 22

An organism that is resistant to high concentrations of the drug but susceptible to low concentrations