Mycology Flashcards
Fungal structure
- 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
yeast
Unicellular form of a fungus
hyphae vs pseudohyphae
hyphae: filamentous form of a fungus
Pseudohyphae: chains of yeast that have the appearance of hyphae
mold
a fungus that grows as a mass of hyphae (mycelium)
endospores
spores contained within a sac
dimorphic fungus
fungi that exist as yeast forms in animal tissues and as hyphae in the environment
budding yeast
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
Germinating Spore/Conidia
fungal growth/reproduction
Forms germ tube that can grow into a new organism
fruiting body
Produces many conidia (spores) that are each very tiny and light and can be dispersed through the environment
arthroconidia
Observed in PATIENTS
Spores release during hyphal fragmentation
dermatophyte spore
macroconidia
observed in lab
dermatophyte reproduction
septate vs non septate hyphae
mycosis
Invasion and destruction of animal tissues by a fungus
Diagnosis of fungal infections
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)
Wet mount cytology
Best for: Superficial skin samples
Mounting Fluid Options:
* 10% Potassium hydroxide: Clears cellular debris, Candida, dermatophytes, Demodex
* New methylene blue
* Lactophenol cotton blue
fungal cultures
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
Dermatophyte test media
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
Dermatophyte
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
Dermatophytosis: Immunity, predisposing factors, clinical signs
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
Dermatophytosis: Diagnosis
Wood’s lamp: flouresce (not specific or sensitive)
Cytology
* Wet mount
* Dried and stained
Fungal culture
Histopathology
Dermatophytosis: Sticky Tape Preparation
add stain and cultured fungus to slide then cover with tape
look for macroconidia
Which macroconidia is which species?
Sporothrix schenckii
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
Respiratory/systemic fungi
Blastomyces dermatitidis
Histoplasma capsulatum
Cryptococcus spp.
Coccidioides immitis
dimorphic
blastomyces cytology
big blue broad budding on cytology
Histoplasma cytology
in histocytes (inc macrophages)
cryptococcus cytology
narrow based budding, with capsule (mucopolysaccharide layer, hides organism from immune system, doesn’t stain).
Coccidioides cytology
endospores
Geographic distribution of respiratory fungi
Crypto
Cocci
Blasto
Histo
Blasto – bodies of water
Histo – likes nitrogen rich soil, bat/pigeon guano
Crypto – gattti is distribution shown, neoformans – worldwide
Cocci – arid environments
pathogenesis of respiratory fungi (Histo, Crypto, Cocci, Blasto)
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
Sites for dissemination of respiratory fungi (Histo, Crypto, Cocci, Blasto)
B: Bones and Brain (CNS)= osteomyelitis, neurologic
E: eyes = enlarged eyes, granuloma
L: lymph nodes = enlarged
L: lungs= generalized nodules
S: skin = lesions
Respiratory fungi diagnosis
Direct visualization
* Blood smear
* Cytology
* Histopathology
Antigen/Antibody detection
* Serum, Urine, CSF
* Titers
Culture
Specialized labs
