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Flashcards in Mycology Deck (22):
1

Mycology

The study of fungi

2

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

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

3

Features of Eukaryotes

Membrane bound nucleus
Endoplasmic reticulum
Mitochondria
Golgi
Lysosomes
Linear chromosomes

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Difference between Fungi and higher Eukaryotic Cells

Fungal membranes contain ergosterol rather than cholesterol
Fungal cells are usually surrounded by a rigid cell wall composed of carbohydrate polymers and protein

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What drug binds ergosterol
What drugs interfere with ergosterol biosynthesis

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

6

Features of Fungi

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

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Yeast morphology

- 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)

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Hyphae/Mycelium

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

9

Types of hypahe

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

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Rhizoids

Rootlike structures

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Asexual Reproductive Elements

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

12

General Fungal Infections

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

13

Mycotoxins

- 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)

14

Diagnostic Laboratory Procedures

- 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

15

Targets of antifungal drugs

Ergosterol
Cell wall synthesis
Nucleic Acid synthesis
Disruption of microtubules

16

Possible effective strategies for combination therapy

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

17

Possible Drawbacks to combination therapy

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

18

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

C. albicans; Candida

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

Efflux Pumps; Target Alterations; Reduced Access to Drug Targets

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Primary resistance

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

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Secondary Resistance

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

22

Eagle Effect

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