Medical Mycology Flashcards
Name six characteristics of fungi.
- Eukaryotic
- Aerobic
- Unicellular or filamentous
- Heterotrophic
- Rigid cell wall
- Reproduce sexually &/or asexually
What is contained in fungal cell walls?
Chitin and Cellulose
What is contained in a fungal cell membrane?
Ergosterol
Define saprobes.
Fungi that live upon dead and decaying organic matter.
Define symbionts
Fungi that live upon another organism to the mutual advantage of both.
Define commensal fungi.
Fungi that live upon another organism with no detriment to the host.
Define parasitic fungi.
Fungi that live upon anthoer organism with clear detriment to the host
What is an “imperfect” fungi?
One that does not reproduce sexually.
What are the two basic growth forms of fungi?
Yeast and Molds
In what two ways do yeast reproduce?
- Budding (to produce blastoconidia)
2. Fission (dividing in half)
Define molds.
Filamentous growth forms.
How do molds reproduce?
Formation of spores or conidia.
What is a hyphae? And how does it differ from mycelium?
Filamentous element. Mycelium is a mass of hyphae.
What are septa?
Septa divide hyphae into compartments, but do NOT strictly divide the fungus into “cells”
How are pseudohyphae different from true hyphae?
Pseudohyphaeare simply elongated yeast linked together. They DO NOT have cytoplasmic connections between compartments. Ex: Candida albicans
Define dimorphic.
A fungus that may exist in yeast or hyphal form. This is different from thermal dimophism because thermal dimophism is a result of a stimulus.
Name the five medically relevant thermally dimorphic organisms.
S- Some Sporothrix schenckii C- Can Coccidioides immitis H- Have Histoplasmosa capsulatum B- Both Blastomyces dermatitidis P- Phases Paracoccidioides brasiliensis
What are rhizoids?
Specialized form of hyphal elements that grow like roots
Describe the hyphae of conidia.
Conidophore- specialized aerial hyphae. Some are large and multinucleated (macroconidia) and small and unicellular (microcondidia)
Describe the hyphae of sporangia.
Asexual spores (endospores) are enclosed in a membranous sac entire structure called sporangiphore.
Describe the hyphae of chlamydospores.
Thick-walled, round spores that are highly resistant to adverse environmental conditions . They can either be terminal (form at the end of hyphae) or intercalary (along and within hyphae).
Describe the hyphae of arthrospores.
Hyphae develop along the hyphae and are more numerous and elongated. “Barrel-shaped”. Inhalation causes disease
Describe the hyphae of spherules
Large spherules in tissues that are filled with endospores.
Describe the hyphae of blastoconidia
Yeast that bud asymmetrically
Describe the sclerotic bodies
Thick-walled, environmentally protective forms of yeast
What is another name for a fungal colony growing on a culture dish?
Thallus
What is the difference between an obverse and a converse.
An obverse is the top side of the growing thallus and the converse is the flip-side.
Where can a geophilic fungus be found?
Soil
Where can a anthrophilic fungus be found?
Humans
Where can a zoophilic fungus be found?
Animals
What can a demitiaceous fungus do?
Produce it’s own pigment
Name three of the most common superficial fungal infections.
- Dermatophytes
- Candida
- Pityrosporum
Which of the superficial fungal infections produces hyphae and utilizes keratin as a substrate for growth.?
Dermatophytes
What important growth factor does candida prefer?
glucose of interstitial fluids
What type of superficial fungus breakdown products of sebum for growth?
Pityrosporum
Are deep mycoses characteristic of of systemic or superficial infections?
Systemic
AIDS patients are at risk for developing what fungal infection?
Systemic cryptococcosis (a thick mucoid capsuled fungus).
Autofluoresce under black light is characteristic of what fungal infection?
Tinea capitis (dermatophyte infection of the scalp)
What type of stain leaves the chitinous walls of fungi more visible to direct microscopic examination?
KOH or the surfactant DMSO
What structure does the addition of chlorazol E black stain to KOH or DMSO stain? What color?
It stains the chitinous fungal cell walls a grey-green color
In what situation would you use India ink?
India ink stains everything but thick mucoid capsules. Use it if you suspect something like cryptococcosis.
What is the chief advantage of culturing fungi?
It allows for direct speciation.
Name three types of media used for culturing fungi.
- Sabouraud’s agar
- Mycosel/mycobiotic agar
- Dermatophyte Test Medium
Name one advantage and one disadvantage to the use of Sabouraud’s agar.
Advantage- Most sensitive
Disadvantage- unrelated contaminants also grow well
What agar is impregnated with chloramphenicol and chlorheximide? And what do these additions do?
They are found in Mycosel agar. And the additions inhibit the growth of bacteria and saprobes.
Which agar has a pH indicator that turns red in the presence of a dermatophyte?
Dermatophyte Test Medium
Cornmeal agar induces what fungi to produce chlamydospores?
Candida albicans
Which of the following tests is more sensitive to the presence of fungi: Culture or KOH?
KOH
What is used to stain fungal specimens taken from colonies grown via culture?
Lactophenol cotten blue
What are some advantages and disadvantages of histology.
Advantages- rapid, high degree of sensitivity
Disadvantages- higher cost, invasive nature, and sporotrichosis is not well demonstrated by histologyT
True or False: PAS/D stains human tissue.
False. PAS/D highlights ehitinous cell wall of fungi. It does not stain human tissue, but it does stain glycogen rich material but stain is lost with diastase digestion.
Which special fungal stain utilizes silver to highlight fungus a jet black color?
Gomori methenamine silver (GMS)
Would you use mucicarmine stain to visualize Cryptococcus?
Yes it is a mucin stain and is highlights the mucoid capsule characteristic of Cryptococcus.
Which stain uses fluroescent microscopy to visualize fungi?
Calcoflour white. The stain binds the cell wall and fluoresces blue/white or apple-green
Can you do a skin test to test for fungal infections?
Yes! Using histoplasmin derived from Histoplasmosa capsulatum
True or False: Can you test the blood for fungi? PCR?
Yup. Also Yup.
What is the action of polyenes?
Amphoteric molecules that bind to ergosterols and have fungicidal actions.
What are two types of polyenes? And what are their actions
- Amphotericin B- binds ergosterols, creates a pore and causes ions and molecules to leave cell. Bad side affects
- Nystatin- polyene used topically for Candida infections
What is the function of 14alpha-demethylase?
It is a fungal enzyme that converts lanosterol to ergosterol.
What antifungal inhibits 14alpha-demethylase and is considered fungistatic?
Imidazoles/Triazoles
What is one drawback of Imidazoles/Triazoles?
Interfere with cytochrome P450 enzymes.
What are triazoles?
A type of imidazole that is newer and better tolerated
What is the function of squalene epoxidase?
A fungal enzyme required for ergosterol synthesis.
What is the role of the antifungal, Allylamines/Benzylamines?
They inhibit the enzyme squalene epoxidase. Leads to an accumulation of squalene which is fungicidal.
Terbinafine is a allylamine that has a prominent side effect of…
unmasking lupus-like condition
What antifungal agent inhibits the synthesis of glucan int he cell wall?
Echinocandins. Fungicidal against Candida and fungistatic against Aspergillus
What does griseofulvin target?
It disrupts mitotic spindle formation and is used in children with tinea capitis. Fungistatic
What does flucytosine target?
Interrupts DNA synthesis and is fungistatic
What does ciclopirox olamine target?
Inhibition of many different fungal enzymes through chelation of polyvalent metal cations.
