Medical Mycology

Question 1

Name six characteristics of fungi.

Answer 1

1. Eukaryotic
2. Aerobic
3. Unicellular or filamentous
4. Heterotrophic
5. Rigid cell wall
6. Reproduce sexually &/or asexually

Question 2

What is contained in fungal cell walls?

Answer 2

Chitin and Cellulose

Question 3

What is contained in a fungal cell membrane?

Answer 3

Ergosterol

Question 4

Define saprobes.

Answer 4

Fungi that live upon dead and decaying organic matter.

Question 5

Define symbionts

Answer 5

Fungi that live upon another organism to the mutual advantage of both.

Question 6

Define commensal fungi.

Answer 6

Fungi that live upon another organism with no detriment to the host.

Question 7

Define parasitic fungi.

Answer 7

Fungi that live upon anthoer organism with clear detriment to the host

Question 8

What is an “imperfect” fungi?

Answer 8

One that does not reproduce sexually.

Question 9

What are the two basic growth forms of fungi?

Answer 9

Yeast and Molds

Question 10

In what two ways do yeast reproduce?

Answer 10

1. Budding (to produce blastoconidia)

2. Fission (dividing in half)

Question 11

Define molds.

Answer 11

Filamentous growth forms.

Question 12

How do molds reproduce?

Answer 12

Formation of spores or conidia.

Question 13

What is a hyphae? And how does it differ from mycelium?

Answer 13

Filamentous element. Mycelium is a mass of hyphae.

Question 14

What are septa?

Answer 14

Septa divide hyphae into compartments, but do NOT strictly divide the fungus into “cells”

Question 15

How are pseudohyphae different from true hyphae?

Answer 15

Pseudohyphaeare simply elongated yeast linked together. They DO NOT have cytoplasmic connections between compartments. Ex: Candida albicans

Question 16

Define dimorphic.

Answer 16

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.

Question 17

Name the five medically relevant thermally dimorphic organisms.

Answer 17

S- Some     Sporothrix schenckii
C- Can       Coccidioides immitis
H- Have     Histoplasmosa capsulatum
B- Both      Blastomyces dermatitidis
P- Phases  Paracoccidioides brasiliensis

Question 18

What are rhizoids?

Answer 18

Specialized form of hyphal elements that grow like roots

Question 19

Describe the hyphae of conidia.

Answer 19

Conidophore- specialized aerial hyphae. Some are large and multinucleated (macroconidia) and small and unicellular (microcondidia)

Question 20

Describe the hyphae of sporangia.

Answer 20

Asexual spores (endospores) are enclosed in a membranous sac entire structure called sporangiphore.

Question 21

Describe the hyphae of chlamydospores.

Answer 21

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).

Question 22

Describe the hyphae of arthrospores.

Answer 22

Hyphae develop along the hyphae and are more numerous and elongated. “Barrel-shaped”. Inhalation causes disease

Question 23

Describe the hyphae of spherules

Answer 23

Large spherules in tissues that are filled with endospores.

Question 24

Describe the hyphae of blastoconidia

Answer 24

Yeast that bud asymmetrically

Question 25

Describe the sclerotic bodies

Answer 25

Thick-walled, environmentally protective forms of yeast

Question 26

What is another name for a fungal colony growing on a culture dish?

Answer 26

Thallus

Question 27

What is the difference between an obverse and a converse.

Answer 27

An obverse is the top side of the growing thallus and the converse is the flip-side.

Question 28

Where can a geophilic fungus be found?

Answer 28

Soil

Question 29

Where can a anthrophilic fungus be found?

Answer 29

Humans

Question 30

Where can a zoophilic fungus be found?

Answer 30

Animals

Question 31

What can a demitiaceous fungus do?

Answer 31

Produce it's own pigment

Question 32

Name three of the most common superficial fungal infections.

Answer 32

1. Dermatophytes 2. Candida 3. Pityrosporum

Question 33

Which of the superficial fungal infections produces hyphae and utilizes keratin as a substrate for growth.?

Answer 33

Dermatophytes

Question 34

What important growth factor does candida prefer?

Answer 34

glucose of interstitial fluids

Question 35

What type of superficial fungus breakdown products of sebum for growth?

Answer 35

Pityrosporum

Question 36

Are deep mycoses characteristic of of systemic or superficial infections?

Answer 36

Systemic

Question 37

AIDS patients are at risk for developing what fungal infection?

Answer 37

Systemic cryptococcosis (a thick mucoid capsuled fungus).

Question 38

Autofluoresce under black light is characteristic of what fungal infection?

Answer 38

Tinea capitis (dermatophyte infection of the scalp)

Question 39

What type of stain leaves the chitinous walls of fungi more visible to direct microscopic examination?

Answer 39

KOH or the surfactant DMSO

Question 40

What structure does the addition of chlorazol E black stain to KOH or DMSO stain? What color?

Answer 40

It stains the chitinous fungal cell walls a grey-green color

Question 41

In what situation would you use India ink?

Answer 41

India ink stains everything but thick mucoid capsules. Use it if you suspect something like cryptococcosis.

Question 42

What is the chief advantage of culturing fungi?

Answer 42

It allows for direct speciation.

Question 43

Name three types of media used for culturing fungi.

Answer 43

1. Sabouraud's agar 2. Mycosel/mycobiotic agar 3. Dermatophyte Test Medium

Question 44

Name one advantage and one disadvantage to the use of Sabouraud's agar.

Answer 44

Advantage- Most sensitive | Disadvantage- unrelated contaminants also grow well

Question 45

What agar is impregnated with chloramphenicol and chlorheximide? And what do these additions do?

Answer 45

They are found in Mycosel agar. And the additions inhibit the growth of bacteria and saprobes.

Question 46

Which agar has a pH indicator that turns red in the presence of a dermatophyte?

Answer 46

Dermatophyte Test Medium

Question 47

Cornmeal agar induces what fungi to produce chlamydospores?

Answer 47

Candida albicans

Question 48

Which of the following tests is more sensitive to the presence of fungi: Culture or KOH?

Answer 48

KOH

Question 49

What is used to stain fungal specimens taken from colonies grown via culture?

Answer 49

Lactophenol cotten blue

Question 50

What are some advantages and disadvantages of histology.

Answer 50

Advantages- rapid, high degree of sensitivity | Disadvantages- higher cost, invasive nature, and sporotrichosis is not well demonstrated by histologyT

Question 51

True or False: PAS/D stains human tissue.

Answer 51

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.

Question 52

Which special fungal stain utilizes silver to highlight fungus a jet black color?

Answer 52

Gomori methenamine silver (GMS)

Question 53

Would you use mucicarmine stain to visualize Cryptococcus?

Answer 53

Yes it is a mucin stain and is highlights the mucoid capsule characteristic of Cryptococcus.

Question 54

Which stain uses fluroescent microscopy to visualize fungi?

Answer 54

Calcoflour white. The stain binds the cell wall and fluoresces blue/white or apple-green

Question 55

Can you do a skin test to test for fungal infections?

Answer 55

Yes! Using histoplasmin derived from Histoplasmosa capsulatum

Question 56

True or False: Can you test the blood for fungi? PCR?

Answer 56

Yup. Also Yup.

Question 57

What is the action of polyenes?

Answer 57

Amphoteric molecules that bind to ergosterols and have fungicidal actions.

Question 58

What are two types of polyenes? And what are their actions

Answer 58

1. Amphotericin B- binds ergosterols, creates a pore and causes ions and molecules to leave cell. Bad side affects 2. Nystatin- polyene used topically for Candida infections

Question 59

What is the function of 14alpha-demethylase?

Answer 59

It is a fungal enzyme that converts lanosterol to ergosterol.

Question 60

What antifungal inhibits 14alpha-demethylase and is considered fungistatic?

Answer 60

Imidazoles/Triazoles

Question 61

What is one drawback of Imidazoles/Triazoles?

Answer 61

Interfere with cytochrome P450 enzymes.

Question 62

What are triazoles?

Answer 62

A type of imidazole that is newer and better tolerated

Question 63

What is the function of squalene epoxidase?

Answer 63

A fungal enzyme required for ergosterol synthesis.

Question 64

What is the role of the antifungal, Allylamines/Benzylamines?

Answer 64

They inhibit the enzyme squalene epoxidase. Leads to an accumulation of squalene which is fungicidal.

Question 65

Terbinafine is a allylamine that has a prominent side effect of...

Answer 65

unmasking lupus-like condition

Question 66

What antifungal agent inhibits the synthesis of glucan int he cell wall?

Answer 66

Echinocandins. Fungicidal against Candida and fungistatic against Aspergillus

Question 67

What does griseofulvin target?

Answer 67

It disrupts mitotic spindle formation and is used in children with tinea capitis. Fungistatic

Question 68

What does flucytosine target?

Answer 68

Interrupts DNA synthesis and is fungistatic

Question 69

What does ciclopirox olamine target?

Answer 69

Inhibition of many different fungal enzymes through chelation of polyvalent metal cations.