Mycology 1: Intro

Question 1

What is fungal cell wall made of?

Answer 1

Polysaccharides beta-glucan and chitin

Question 2

What stains in KOH prep?

Answer 2

Cell wall

Question 3

What are the only 2 fungi that make up normal microbiota?

Answer 3

Candida albicans and Malassezia furfur

Question 4

What parts of CMI aid in fungal host defense?

Answer 4

CD4 T cells and macrophages

Question 5

What are 2 examples of fungi that exist only as yeast?

Answer 5

Cryptococcus neoformans and Candida glabrata

Question 6

What 3 fungi exist purely as a mold?

Answer 6

Aspergillus, Dermatophytes, Zygomycetes

Question 7

2 transition states

Answer 7

Germ tubes - elongation of yeasts into hyphae

Pseudohyphae - budding of yeast w/o fully separating.

Question 8

Ascomycetes

Answer 8

2 compatible haploid nuclei fuse to form a diploid nucleus, followed by meiosis to form haploid progeny. Form spores w/in a sac called an ascus

Question 9

Basidiomycetes

Answer 9

Similar to ascomycetes but early part occurs w/in a sac called the basidium, and then haploid progeny mature on the outer surface of that basidium (mushrooms).

Question 10

Zygomycetes

Answer 10

Gametes fuse to form a zygote (similar to humans)

Question 11

Deuteromycetes

Answer 11

No sexual stage has been identified

Question 12

4 examples of mycotoxins

Answer 12

• Aflatoxins – Aspergillus often grows on corn or peanuts. Does not affect humans due to food inspection, but may cause cirrhosis in poultry.
• Ergot alkaloids from Claviceps purpurea in grains / breads cause vasoconstriction, peripheral necrosis, and gangrene
• Fumonisins may cause neural tube defects
• Trichothecenes from Stachybotrys or Fusarium

Question 13

Top 2 outdoor allergens

Answer 13

Pollens and fungi

Question 14

Top 2 indoor allergens

Answer 14

Dust mites and fungi

Question 15

What causes cheese-washer’s disease?

Answer 15

Penicillium

Question 16

What molecules are mycotoxins made of?

Answer 16

Low MW secondary metabolites

Question 17

General tx for superficial fungal infections

Answer 17

Topical / systemic antifungals for cosmetic reasons.

Question 18

Tinea / pityriasis versicolor
Causative fungus
Morphology
Requirement
Sxs
Mechanism
Tx

Answer 18

Malassezia furfur (normal microbiota)
Dimorphic. Mold is pathogenic. Yeast is commensal. Spaghetti and meatballs.
•Lipophilic – requires exogenous FA’s, from human sebaceous / oily skin
Causes flaking / scaling of skin w/ hyper / hypo pigmentation.
Mechanism - disordered host melanin production –> hyper pigmentation. Fungal metabolite azelaic acid –> hypopigmentation.
Tx w/ topical antifungals.

Question 19

3 other diseases caused by Malassezia

What type of pxs?

Answer 19

Often occurs in HIV pxs
•Seborrheic dermatitis – mainly affects face and axilla
•Dandruff / cradle cap – Scaling. Often affects newborns.
•Rare dissemination – mainly in premature infants receiving total parenteral nutrition (TPN). IV nutrition includes daily bolus of lipids, which is a good opportunity for Malassezia to enter blood stream

Question 20

What is the most common fungal infection?

Answer 20

Cutaneous mycoses (dermatophytes)

Question 21

What are the 3 genera of dermatophytes?

Answer 21

•Trichophyton, Microsporum, and Epidermophyton.

Question 22

3 characteristics of cutaneous mycoses

Answer 22

Keratinophilic w/ keratinases
Highly contagious (rare for fungus)
May be geophilic, zoophilic, or anthropomorphic.

Question 23

Tinea infections
Manuum
Fabis
Barbae

Answer 23

Manuum = hand (may be nodular)
Fabis = severe scalp infection w/ alopecia
Barbae = beared area

Question 24

Kerion

Answer 24

Superficial skin infection

Kerion = abscess that can be superinfected by skin bacteria such as staph or strep.

Question 25

What causes subcutaneous mycoses?

Which skin layers?

Answer 25

Trauma or mucus membranes (sinuses / eyes). Immunocompromise / diabetes may be present.
Involves epidermis, dermis, and subQ. Hydrolytic enzymes may cause destruction of fascia / bone.

Question 26

Sporothrix schenckii / Sporotrichosis
Morphology
Other names / associations
Diseases (3)

Answer 26

• Dimorphic – Mold in soil (infectious form; mycelia and conidia). Yeast in host (pathogenic). Yeast are fusiform / cigar-shaped.
• Asteroid body – central yeast cell surrounded by radiating red projections
• Gardener’s / Rose picker’s disease, associated w/ potting soil / sphagnum moss.
• Lymphocutaneous sporotrichosis – Most common manifestation. Small, hard, painless nodule develops, becomes fixed, and enlarged to form a fluctuant mass that eventually ulcerates. Nodules may “track” along lymphatics, but stays relatively regional.
• Inhalation can cause pulmonary or disseminated sporotrichosis, mainly in immunocompromised pxs. Not actually subcutaneous.
• Fixed cutaneous sporotrichosis – dry crusty surface lesion at site of infection w/o lymphatic progression. Often occurs in previously infected pxs who developed immune responses sufficient to contain the infection more quickly.

Question 27

Zygomycosis / mucormycosis
3 types of Mucorales
Morphology
General characteristics
Sites of infection
Mucor morphology
Risk factors for zygomycosis
Rhinocerebral zygomycosis

Answer 27

Rhizopus, Mucor, and Absidia
•Fast growing, saprobic, soil molds. Progressive tissue infection, often rapidly invasive / destructive
•Exist only as molds
•Enters via break in skin or inhalation. Lungs and sinuses are common spots of infection. Usually involves immunocompromise.
•Mucor - Broad, ribbon-like, aseptate hyphae. 90 degree branching
•Risk factors for zygomycosis – neutropenia, immunosuppressive therapy, iron chelation therapy, acidosis (low pH causes iron release from transferrin which is taken up by zygomycetes), diabetes (high glucose for nutrition and diminished phagocyte activity), DIABETIC KETOACIDOSIS
•Rhinocerebral zygomycosis – Sinus infection extending to brain. Rapidly progressive (hours / days), fulminant, and life threatening. Mainly seen in diabetic / acidotic pxs (diabetic ketoacidosis), neutropenic pxs, or those on immunosuppressive therapy.

Question 28

How are nail / hair dermatophyte infections treated differently than skin infections?

Answer 28

Nail / hair infections require oral azoles / terbinafine. Topical skin infections only require topical azoles / terbinafine.