Mycology 7

Question 1

Describe the fungal cell

Answer 1

• Typically eukaryotic cell
• Two important differences
  1) Cell Wall (not the same as bacteria)
  2) Membrane sterol composition

Question 2

define the fungal cell wall

Answer 2

Function: provide shape, rigidity, strength, protection from osmotic shock
Contains: carbohydrates and proteins (may be antigenic/immunogenic)
- type and amount of the polysaccharides vary from one fungal species to other.

Question 3

Define the fungal cell membrane

Answer 3

Function: contain cytoplasm, regulate nutrient flow, etc
Structure: Typically phospholipid bilayer
- unique sterol composition (humans = primarily cholesterol; fungi = primarily ergosterol)

Question 4

define Yeast

Answer 4

• UNICELLULAR - spherical or ellipsoid shape
• REPRODUCE by a process known as budding
• Under proper conditions some yeast form structures known as pseudohyphae (buds never separate and become elongated)

Question 5

Define Molds

Answer 5

• Hyphae (individual strands of molds)
• Mycelium (clusters of molds) can grow into vegetative or aerial
• Reproduction = asexual produce conidia; Sexual produce spores

Question 6

Describe the types of fungal infections:

Superficial, Cutaneous, subcutaneous, Systemic, Opportunistic

Answer 6

SUPERFICIAL MYCOSES = infection of the outermost layers of the skin and hair
CUTANEOUS MYCOSES = infection which extends deep into the epidermis as well as invasive hair and nail infection
SUBCUTANEOUS MYCOSES = Infections involving the dermis, subcutaneous tissues, muscle, and fascia
SYSTEMIC MYCOSES = infections that originate primarily in the lung but may spread to any organ in the body
OPPORTUNISTIC MYCOSES = infection associated primarily with immunosupressed individuals

Question 7

Describe the host response/immunity to fungi

Answer 7

• *Innate immune system of a healthy individual is generally sufficient to prevent fungal infection
• intact skin, pH, competition with the normal bacterial flora, epithelial turnover rate, desiccated nature of the stratum corneum, mucous membranes
• • When these protective barriers are breached fungi gain access to, colonize and multiply in host tissues
• • Fungi can gain access to host tissues by traumatic implantation or inhalation
• *LITTLE ROLE FOR HUMORAL IMMUNITY (ANTIBODIES)
• • Cell mediated immunity is essential for controlling and eliminating infection.

Question 8

Describe antifungal drugs

Answer 8

Topical therapy - superficial and most cutaneous infection

Systemic therapy - subcutaneous and systemic infections, some cutaneous

Question 9

Describe the antifungal drugs that target cell membrane

Answer 9

Cell membrane = Ergosterol synthesis
Drugs:
Azoles
Allylamines
Thiocarbamates
Morpholines

Question 10

Define Amphotericin B

Answer 10

Polyene that binds to ergosterol to inhibit cell membrane synthesis (forms a pore/channel that causes osmotic lysis)

Question 11

Describe Echinocandins

Answer 11

Cell wall synthesis inhibitors via inhibition of Beta-glucan synthesis

• Highly selective, but limited to a handful of diseases causing fungi
• Used primarily to treat candida and aspergillus

Question 12

Describe KOH Preparation

Answer 12

• Potassium hydroxide may be used to examine hair, nails, skin scrapings, fluids, exudates, or biopsies
• Fungal structures such as hyphae, large yeast, spherules, and sporangia may be observed
• Specimens placed in a drop of 15% KOH will dissolve at a greater rate than fungi because fungi have chitinous cell walls.
• Visualization of fungi can be further enhanced by the addition of several dyes

Question 13

ALL FUNGI STAIN ________

Answer 13

GRAM POSITIVE

Question 14

What does the Germ Tube test for?

Answer 14

CANDIDA ALBICANS

Question 15

What does india ink stain for?

Answer 15

Cryptococcus neoformans