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Disease and Defense > Medical Mycology > Flashcards

Medical Mycology Flashcards

1
Q

Name six characteristics of fungi.

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

What is contained in fungal cell walls?

A

Chitin and Cellulose

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3
Q

What is contained in a fungal cell membrane?

A

Ergosterol

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4
Q

Define saprobes.

A

Fungi that live upon dead and decaying organic matter.

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5
Q

Define symbionts

A

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

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6
Q

Define commensal fungi.

A

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

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7
Q

Define parasitic fungi.

A

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

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8
Q

What is an “imperfect” fungi?

A

One that does not reproduce sexually.

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9
Q

What are the two basic growth forms of fungi?

A

Yeast and Molds

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10
Q

In what two ways do yeast reproduce?

A
  1. Budding (to produce blastoconidia)

2. Fission (dividing in half)

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11
Q

Define molds.

A

Filamentous growth forms.

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12
Q

How do molds reproduce?

A

Formation of spores or conidia.

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13
Q

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

A

Filamentous element. Mycelium is a mass of hyphae.

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14
Q

What are septa?

A

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

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15
Q

How are pseudohyphae different from true hyphae?

A

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

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16
Q

Define dimorphic.

A

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.

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17
Q

Name the five medically relevant thermally dimorphic organisms.

A 
S- Some     Sporothrix schenckii
C- Can       Coccidioides immitis
H- Have     Histoplasmosa capsulatum
B- Both      Blastomyces dermatitidis
P- Phases  Paracoccidioides brasiliensis
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18
Q

What are rhizoids?

A

Specialized form of hyphal elements that grow like roots

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19
Q

Describe the hyphae of conidia.

A

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

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20
Q

Describe the hyphae of sporangia.

A

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

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21
Q

Describe the hyphae of chlamydospores.

A

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).

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22
Q

Describe the hyphae of arthrospores.

A

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

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23
Q

Describe the hyphae of spherules

A

Large spherules in tissues that are filled with endospores.

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24
Q

Describe the hyphae of blastoconidia

A

Yeast that bud asymmetrically

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25
Q

Describe the sclerotic bodies

A

Thick-walled, environmentally protective forms of yeast

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26
Q

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

A

Thallus

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27
Q

What is the difference between an obverse and a converse.

A

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

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28
Q

Where can a geophilic fungus be found?

A

Soil

29
Q

Where can a anthrophilic fungus be found?

A

Humans

30
Q

Where can a zoophilic fungus be found?

A

Animals

31
Q

What can a demitiaceous fungus do?

A

Produce it’s own pigment

32
Q

Name three of the most common superficial fungal infections.

A
  1. Dermatophytes
  2. Candida
  3. Pityrosporum
33
Q

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

A

Dermatophytes

34
Q

What important growth factor does candida prefer?

A

glucose of interstitial fluids

35
Q

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

A

Pityrosporum

36
Q

Are deep mycoses characteristic of of systemic or superficial infections?

A

Systemic

37
Q

AIDS patients are at risk for developing what fungal infection?

A

Systemic cryptococcosis (a thick mucoid capsuled fungus).

38
Q

Autofluoresce under black light is characteristic of what fungal infection?

A

Tinea capitis (dermatophyte infection of the scalp)

39
Q

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

A

KOH or the surfactant DMSO

40
Q

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

A

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

41
Q

In what situation would you use India ink?

A

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

42
Q

What is the chief advantage of culturing fungi?

A

It allows for direct speciation.

43
Q

Name three types of media used for culturing fungi.

A
  1. Sabouraud’s agar
  2. Mycosel/mycobiotic agar
  3. Dermatophyte Test Medium
44
Q

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

A

Advantage- Most sensitive

Disadvantage- unrelated contaminants also grow well

45
Q

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

A

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

46
Q

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

A

Dermatophyte Test Medium

47
Q

Cornmeal agar induces what fungi to produce chlamydospores?

A

Candida albicans

48
Q

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

A

KOH

49
Q

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

A

Lactophenol cotten blue

50
Q

What are some advantages and disadvantages of histology.

A

Advantages- rapid, high degree of sensitivity

Disadvantages- higher cost, invasive nature, and sporotrichosis is not well demonstrated by histologyT

51
Q

True or False: PAS/D stains human tissue.

A

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.

52
Q

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

A

Gomori methenamine silver (GMS)

53
Q

Would you use mucicarmine stain to visualize Cryptococcus?

A

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

54
Q

Which stain uses fluroescent microscopy to visualize fungi?

A

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

55
Q

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

A

Yes! Using histoplasmin derived from Histoplasmosa capsulatum

56
Q

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

A

Yup. Also Yup.

57
Q

What is the action of polyenes?

A

Amphoteric molecules that bind to ergosterols and have fungicidal actions.

58
Q

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

A
  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
59
Q

What is the function of 14alpha-demethylase?

A

It is a fungal enzyme that converts lanosterol to ergosterol.

60
Q

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

A

Imidazoles/Triazoles

61
Q

What is one drawback of Imidazoles/Triazoles?

A

Interfere with cytochrome P450 enzymes.

62
Q

What are triazoles?

A

A type of imidazole that is newer and better tolerated

63
Q

What is the function of squalene epoxidase?

A

A fungal enzyme required for ergosterol synthesis.

64
Q

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

A

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

65
Q

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

A

unmasking lupus-like condition

66
Q

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

A

Echinocandins. Fungicidal against Candida and fungistatic against Aspergillus

67
Q

What does griseofulvin target?

A

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

68
Q

What does flucytosine target?

A

Interrupts DNA synthesis and is fungistatic

69
Q

What does ciclopirox olamine target?

A

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

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