Mycology Flashcards
What is the structure of the cell well of fungi?
Rigid cell wall r/t chitin
Matrix of polysaccharides, proteins, and lipids
Also contains ergosterol
This structure makes them resistant to hostile env
What are the 3 morphological classifications of fungi?
Yeast
Mold
Dimorphic fungi
What are the 3 most common medically important dimorphic fungi?
Histoplasma capsulatum
Blastomyces dermatitidis
Coccidioides immitis
Yeast are (uni/multi)cellular, reproduce by (spore/budding/binary fission) <- more than 1
Unicellular; budding or binary fission
What is the appearance of yeast on media?
Moist, creamy, opaques colonies
Mold are (uni/multi)cellular, reproduce by (spore/filament/budding)
Multicellular; spore
What is the appearance of mold on media?
Fluffy, cottony, woolly, or powdery colonies
What is unique about dimorphic fungi compared to the other 2 types of fungi?
Act differently depending on temperature
Yeast phase at warmer temp (35-37)
Filamentous molds form at 30-25
Which phase of dimorphic fungi is it infectious?
Yeast phase
What are the 4 steps in the lab dx of fungal infection?
specimen collection and timely transport to lab
Direct examination
Fungal culture
Rapid commercial identification tests
This substance is used to digest debris and clear keratinized tissue so the fungi present can be visualized
KOH
Once KOH is used to clear debris, this substance is used to stain the fungi. It binds to the chitin in the fungal cell wall and becomes fluorescent under fluoroscopy microscope.
Calcofluor white
What is the most used fungal stain for culture growth?
Lactophenol cotton blue (LPCB) wet mount
What steps are involved in preparing a LPCB wet mount?
Phenol: kills live organisms (lab biosafety)
Lactic acid: preserves fungal structures
Cotton blue stains chitin on fungal walls
What commercial methods can be used to identify yeast?
CHROM agar
Vitek yeast identification system
MALDI
Pseudohyphae are a characteristic associated with yeast cells. What are they?
Elongated yeast cells that remain attached to one another
Cells are separated by obvious constriction site
See slide 12
What is an IV anti fungal that can be used for yeast?
Caspofungin
What is C. Kruzei intrinsically resistant to?
Fluconazole
What is candidemia?
Infection of the blood with Candida (yeast)
A blood culture is obtained from a patient and grows candida spp. in 1/4 of the cultures grown. Is there a chance this is contamination?
No; candida in blood culture should never be viewed as a contaminant and should prompt evaluation and empiric treatment
What pts are at high risk for candidemia?
IC
Central line
TPN
Broad spec antibiotic
Abd sx
How often should blood cultures be repeated with a fungal infection to confirm it is cleared from the blood?
48-72hrs
A patient has received a negative culture for yeast after being on caspofungin for 1wk. How much longer should therapy be continued after a negative culture?
2 wks after the documented negative culture
In what regions of the world is histoplasma capsulatum most common?
Midwestern and Central USA along the Ohio and Mississippi River
Where is histoplasma capsulatum found in Canada?
St. Lawerence River
Alberta
Northwestern New Brunswick
what are some reservoirs of histoplasma capsulatum?
Soil contaminated with bird or bat droppings
This fungus mimics symptoms of TB making it important to ask pts about travel history
Histoplasma capsulatum
What kind of fungi (yeast/mold/dimorphic fungi) is histoplasma capsulatum?
Dimorphic fungi
What kind of fungi (yeast/mold/dimorphic fungi) is blastomyces dermatitidis?
Dimorphic fungi
Where is blastomyces dermatitidis found in the USA?
Ohio and Mississippi River valleys
Where is blastomyces dermatitidis found in Canada?
Ontario
Quebec
Manitoba
Saskatchewan
What is a morphological feature seen on staining that is key for identifying blastomyces dermatitidis?
Broad based budding
Coccidiodes immitis is endemic to what regions?
Desert regions of the USA
Central and South America
What is a key morphological feature that is strongly indicative of coccidioides immitis?
Barrel shaped arthroconidia that alternate with empty cells
