Mycology (fungi)

Question 1

3 key points about Fungi

Answer 1

• Nosocomial infections
• Opportunistic infections
• Few are primary pathogens

Question 2

Chitin

Answer 2

Used to create the cell wall in fungi

- “Calcofluor white” when stained with calcium

Question 3

Ergosterol

Answer 3

Sterol in fungi cell membrane (human equiv = cholesterol)

• Regulates passage of molecules through membrane
• Antifungal drugs (Amphotericin B) aim to affect ergosterol synthesis

Question 4

Describe the types of fungi

Answer 4

Mold, Yeast, Thermally dimorphic

Question 5

Mold

Answer 5

• Body of fungus/masses of hyphae = “thallus”

- ex. Aspergillus

Question 6

Yeast

Answer 6

1. Reproduces by budding
   - “Pseudohyphae” when it fails to detach
   - Ex. Candida albicans invades as pseudohyphae
2. Can be non-pathogenic
   - Ex. Saccharomycens (ethanol for wine, CO2 for bread)
3. Capable for facultative anaerobic growth
   * Important for invasiveness

Question 7

What is Cryptococcus neoformans and its virulence factor?

Answer 7

• A yeast

- VF: polysaccharide capsule

Question 8

Thermally dimorphic fungi

Answer 8

• Can grow as mold (20C) or yeast (37); temperature dependent
• Ex. Sporothrix (rose gardener’s disease)

Question 9

Sporothrix

Answer 9

Rose Gardener’s Disease

• Subcutaneous infection by a dimorphic fungi
• Fungal spores are introduced into wound after trauma
• Commonly results in lymphangitis on arms + legs
• Causes ulcer formations as it progresses

Question 10

How do bacteria reproduce?

Answer 10

Formation of spores called “conidas”

- Also important for identification

Question 11

Nutritional demands of fungi

Answer 11

• Less nutritionally demanding than bacteria
• Grow better than bacteria in extreme conditions
• Most are aerobic + grow best @25-30C

Question 12

Mycosis (pl. mycoses)

Answer 12

Fungal diseases

Question 13

Superficial mycoses

Answer 13

• Infects the surface of hair shafts + outer skin layer

- Mild infections: Black & White Piedra; Malassezia furfur

Question 14

Cutaneous mycoses

Answer 14

• Infects deeper layers of epidermis (ex. athletes foot, ringworm)
• Caused by dermatophytes (uses keratin as carbon source/food)
• 3 different moulds, same MOP
• Clinical diseases are called “tineas”

Question 15

Systemic mycoses

Answer 15

• Infections in the deep tissues
• Caused by primary + opportunistic pathogens
• Most severe

Question 16

Black and white piedra

Answer 16

A superficial mycosis

- Hair gets brittle and breaks off

Question 17

Malassezia furfur

Answer 17

Superficial mycosis

- Discolorization of skin (commonly due to yeast)

Question 18

Dermatophytes

Answer 18

• Causes cutaneous fungal infections

- Degrades + uses keratin as carbon source/food

Question 19

Tineas

Answer 19

Clinical cutaneous fungal infections

Question 20

Candidasis albicans

Answer 20

Opportunisitic fungus, yeast-like

• Causes vulvo-vaginal candidasis + thrush in mouth and throat
• Common cause of mouth + throat infections in neonates + immunocomp.
• Can be treated with broad-spectrum ABs
• Normal flora in the gut + mouth

Question 21

Antiseptic + example

Answer 21

Disinfectant used on the skin

- Hand sanitizer, mouthwash

Question 22

Disinfectant

Answer 22

Chemicals used to destroy many microorganisms + viruses

- SURFACES

Question 23

Pasteurization

Answer 23

Brief heat treatment used to reduce the # of organisms + kill pathogenic organisms

Question 24

Sanitization

Answer 24

Reduction of the # of organisms to a level that meets public health standards
- Ex. Washing clothes

Question 25

Sterilization

Answer 25

destruction of all forms of microorganisms + inactivation of spores

Question 26

Describe the types of isolation rooms

Answer 26

Negative pressure: room air can't go outside | Positive pressure: corridor air can't get inside the room

Question 27

HEPA

Answer 27

High efficiency particulate air ventilation used in OR

Question 28

Describe 4 ways in which sterilization can be achieved.

Answer 28

1. Heat (hot air for 1-2 days; Autoclaving to inactivate bacterial spores) 2. Irridation - Gamma or UV (expose food to ionizing radiation to destroy microorgs) 3. Filtration 4. Chemicals

Question 29

Autoclaving

Answer 29

Spore Test: sterilization of bacterial spores - Ampule of nutrient media + spores of non-pathogenic bacteria are autoclaved w/ object to be sterilized (instruments), then ampule is incubated - Growth is indicated by change in pH of ampule (=change in color)

Question 30

What determines the efficiency of sterilization?

Answer 30

If the object is free of organic matter (blood, fecal material, etc.) - If not, plaque formation

Question 31

What are halogens?

Answer 31

They are chemical agents that sterilize if appropriate amount is used + prolonged time of exposure CHLORINE - Strong oxidizing agent (ex. Chlorox) - Good for backpackers for decontaminating water (5-10 min) IODINE - Available as tincture (dissolved in alcohol) or as an iodaphor (combo w/ organix matter that slowly release iodine)

Question 32

Viruses with envelopes are more sensitive to disinfectants than naked viruses. True or False?

Answer 32

TRUE because it is a lipid envelope

Question 33

Why are alcohol-based sanitizers inappropriate for naked viruses + endospore-containing organisms?

Answer 33

They kill bacteria + fungi, but don't deactivate endospores + non-enveloped viruses.

Question 34

Alcohols

Answer 34

- Kill bacteria + fungi, but don't deactivate endospores + non-enveloped viruses - Protein denaturation + disruption of lipid membrane - Used for skin degerming - Not good for treating wounds b/w they cause coagulation of proteins (creates enviro where bacteria can grow inside scab) - Optimal [ethanol] = 70% - Isopropanol (rubbing alcohol) > ethanol because it doesn't evaporate as fast

Question 35

What is the least and most susceptible towards chemical agents?

Answer 35

Least: Prions Most: enveloped viruses