Mycology

Question 1

Fungal structure

Answer 1

• Fungi are eukaryotic
• Cell membrane differs from animals (Ergosterol instead of cholesterol)
• Have a cell wall, but cannot make their own energy
• Chitin difficult for immune cells to digest

Question 2

yeast

Answer 2

Unicellular form of a fungus

Question 3

hyphae vs pseudohyphae

Answer 3

hyphae: filamentous form of a fungus
Pseudohyphae: chains of yeast that have the appearance of hyphae

Question 4

mold

Answer 4

a fungus that grows as a mass of hyphae (mycelium)

Question 5

endospores

Answer 5

spores contained within a sac

Question 6

dimorphic fungus

Answer 6

fungi that exist as yeast forms in animal tissues and as hyphae in the environment

Question 7

budding yeast

Answer 7

Fungi reproduce both sexually and asexually
Yeast reproduce asexually by budding
The type of budding allows us to differentiate between different organisms on cytology (can be either):
* Broad-based
* Narrow-based

Question 8

Germinating Spore/Conidia

Answer 8

fungal growth/reproduction
Forms germ tube that can grow into a new organism

Question 9

fruiting body

Answer 9

Produces many conidia (spores) that are each very tiny and light and can be dispersed through the environment

Question 10

arthroconidia

Answer 10

Observed in PATIENTS
Spores release during hyphal fragmentation
dermatophyte spore

Question 11

macroconidia

Answer 11

observed in lab
dermatophyte reproduction

Question 12

septate vs non septate hyphae

Answer 12

Question 13

mycosis

Answer 13

Invasion and destruction of animal tissues by a fungus

Question 14

Diagnosis of fungal infections

Answer 14

Presumptive: Clinical signs, History
Direct Exam/Observation: Cytology, Impression smear, Histopathology
Culture: Can be dangerous for some organisms!
Antibody detection: Serum
Antigen detection: Serum or urine
PCR (not widely used)

Question 15

Wet mount cytology

Answer 15

Best for: Superficial skin samples
Mounting Fluid Options:
* 10% Potassium hydroxide: Clears cellular debris, Candida, dermatophytes, Demodex
* New methylene blue
* Lactophenol cotton blue

Question 16

fungal cultures

Answer 16

send out:
* Fresh tissue/fluid =Always best!
* Swab: Only use when you cannot get a better sample
* Overnight shipping to lab
* Transport Conditions:
Dermatophytes: hair/nails/scales/skin in a sterile container at room temperature
Fungal disease the primary differential: room temperature
Bacterial contamination or differential diagnoses: Send chilled on ice

In house:
Dermatophyte culture media
* DTM – dermatophyte test media
* RSM – Rapid sporulation media

Question 17

Dermatophyte test media

Answer 17

DTM has pH indicator in media
Starts as yellow (A), but when a dermatophyte grows (B), it changes the media pH, which then changes the color of the agar
pH change occurs when organism eats protein in agar > ammonia byproduct > increases pH > agar turns red
False positives can occur if you wait too long to read to results

Question 18

Dermatophyte

Answer 18

Fungal organism that causes ringworm (superficial infections of the skin, hair, and nails)
Infectious agents
* Microsporum spp
* Trichophyton spp

Affected species: Animals, birds, humans
Keratinized structures
* Zoophilic: prefer animals
* Geophilic: prefer environment
* Anthropophilic: prefer humans

Question 19

Dermatophytosis: Immunity, predisposing factors, clinical signs

Answer 19

Protective innate immunity
* Intact & dry epidermis
* Normal skin flora
* Adequate sebum
* Normal grooming
* Cell-mediated immunity

Predisposing factors:
* Skin abrasions, bites
* Moisture
* Excessive grooming
* Immune suppression

Clinical signs:
* Hair loss (alopecia)
* Scales
* Crusts
* Red skin (erythema)
* Pruritis (variable)
* Papules/pustules/kerion

Question 20

Dermatophytosis: Diagnosis

Answer 20

Wood’s lamp: flouresce (not specific or sensitive)
Cytology
* Wet mount
* Dried and stained

Fungal culture
Histopathology

Question 21

Dermatophytosis: Sticky Tape Preparation

Answer 21

add stain and cultured fungus to slide then cover with tape
look for macroconidia

Question 22

Which macroconidia is which species?

Answer 22

Question 23

Sporothrix schenckii

Answer 23

Dimorphic fungus (different form in animal vs environment)
Habitat: soil, dead vegetation, roses, Cats
Sporotrichosis
* Cats, dog, horse, human
* Abrasion/puncture
* Cutaneous, lymphocutaneous, disseminated

Diagnosis: macrophage filled with oval yeast

Question 24

Respiratory/systemic fungi

Answer 24

Blastomyces dermatitidis
Histoplasma capsulatum
Cryptococcus spp.
Coccidioides immitis

dimorphic

Question 25

blastomyces cytology

Answer 25

big blue broad budding on cytology

Question 26

Histoplasma cytology

Answer 26

in histocytes (inc macrophages)

Question 27

cryptococcus cytology

Answer 27

narrow based budding, with capsule (mucopolysaccharide layer, hides organism from immune system, doesn’t stain).

Question 28

Coccidioides cytology

Answer 28

endospores

Question 29

Geographic distribution of respiratory fungi

Crypto
Cocci
Blasto
Histo

Answer 29

Blasto – bodies of water
Histo – likes nitrogen rich soil, bat/pigeon guano
Crypto – gattti is distribution shown, neoformans – worldwide
Cocci – arid environments

Question 30

pathogenesis of respiratory fungi (Histo, Crypto, Cocci, Blasto)

Answer 30

Inhale spores > change forms in the airways (to yeast or endospore).
May stay in lung or disseminate throughout the body via lymphatics or by blood

Question 31

Sites for dissemination of respiratory fungi (Histo, Crypto, Cocci, Blasto)

Answer 31

B: Bones and Brain (CNS)= osteomyelitis, neurologic
E: eyes = enlarged eyes, granuloma
L: lymph nodes = enlarged
L: lungs= generalized nodules
S: skin = lesions

Question 32

Respiratory fungi diagnosis

Answer 32

Direct visualization
* Blood smear
* Cytology
* Histopathology

Antigen/Antibody detection
* Serum, Urine, CSF
* Titers

Culture
Specialized labs