Fundamentals of Fungi Flashcards
What you expect to see in a PAS stained microscopic section from a lung biopsy of
disseminated infection with Blastomyces dermatitidis?
A. Tiny red rods with no nuclear membrane
B. Purple diplococci seen only well on oil immersion.
C. Budding ovals stained hot pink red.
D. Dark gray filaments with little branching
E. Flagellated cells with prominent nuclei staining blue.
C
First you needed to recognize Blastomyces as the name of a dimorphic fungus and then remember what form the fungus would take in the body (yeast) and then to remember that fungi on a PAS will show up as hot pink-red color so the answer is the third choice.
A new pathogen is found. Which of the following compounds would suggest that the agent is a fungus? A. Peptidoglycan B. Teichoic acid C. Endotoxin D. Chlorophyll E. Ergosterol
E
Ergosterol is the dominant sterol in the fungal membranes. Peptidoglycan and teichoic acids are
unique to bacteria. Gram negative bacteria have endotoxin. A few fungi or endotoxin-like compounds. Fungi are heterotrophic, deriving their nutrition from organic compounds so are not photosynthetic so do not have chlorophyll.
An auto mechanic in NJ develops Valley Fever caused by Coccidioides immitis even though he has never been to the endemic area in SE US. He does remember changing the oil on a car from California a few weeks ago. You have seen the slides of the organism from his lungs. If you are one of House, MD’s residents and you had to go out to the California car (with a fitted respirator mask on for safety) and get sand out of the bottom of the car and look for the fungus under the microscope back in the lab, what fungal forms would you be looking for in the ?
A. A form that look just like the forms in the lung.
B. A yeast or yeast like form
C. Spores and possibly hyphae
D. Hyphae
C
Coccidioides is a dimorphic fungus. This means it has filamentous forms and spores found in nature and the more yeast-like form (Although in this case it is not actually yeast like at all!) found in the lungs. So the Answer is C (remember mold is the name for hyphal forms.)
List the four major genera comprising the major US dimorphic pathogens.
Dimorphic fungi
• Fungi exist as mold/filamentous/hyphal form or as yeast
- Generally, in the environment (25-30°C) a dimorphic fungus will grow as a mold
- At 37°C, it will grow as a yeast
- In the cold, it’s the mold
The major US dimorphic pathogens are the genera:
• Histoplasma
• Blastomyces • Coccidioides • Sporothrix
What is Conidia?
- Produced by filamentous fungi on surfaces (nasal passages; leftovers; in lab cultures)
- Airborne-most 3 micron range
- Used in identification of fungal cultures
- Found in huge numbers in compost piles, moldy leftovers.
- Dangerous to transplant patients and other immunocompromised pts.
What is Blastoconidia?
- Formed by yeasts like Candida albicans or other dimorphic fungi in their yeast stage
- Blastoconidia = blastospores = buds (asexual spores)
What is Arthroconidia?
- These are spores formed by fragmentation of hyphae.
- This may occur in tissue (like skin) or environment
- They are released by a process of breakage at the “joints.”
Stain and result to test for fungi?
Periodic Acid Schiff (PAS) reaction: fungi pink (hot)
enzyme that causes Candida infections
proteinase
fungal pathogenesis
- Stimulate the immune system which leads to damage through cytokines and cell-mediated immune response
- Zymosan found in the fungal cell walls resembles endotoxin and triggers production of TNF
- Growth may invade blood vessels; vegetations may grow on heart
- Both may lead to infarcts
- Fungi may damage by producing enzymes
Test for Cryptococcal meningitis
CSF-India Ink (nigrosin) wet mount
common in AIDS patients
A “rule in” test only (misses 50% of cases. If positive, it provides a rapid diagnosis but other tests and cultures must also be done
