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STEP 1 Microbiology > General- Fungi and antifungals > Flashcards

General- Fungi and antifungals Flashcards

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Biology 101 flashcards
1
Q

How do yeasts divide?

A

Budding

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2
Q

Describe yeast colonies on solid agar

A

Bacteria-like

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3
Q

How do molds grow?

A

Thread-like strands called hyphae

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4
Q

How do mold colonies appear on agar?

A

Filamentous or mycelial

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5
Q

Components of fungal cell wall

A

Manno-proteins, beta-glucan, and chitin

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6
Q

Which type of hyphae are more durable to grinding and mechanical stress?

A

Septate

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7
Q

What are conidia?

A

“Spores” in laymens terms (incorrect). Asexual reproducive structures. Found on structures called conidiophores.

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8
Q

What is the Sabourad agar used for?

A

Fungal culture

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9
Q

At what temperature are fungi cultured?

A

30 degrees C (close to ambient temperature; compare to bacteria cultured at 37 degrees C)

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10
Q

What can India ink be used for?

A

Cryptococcus but NO LONGER RECOMMENDED

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11
Q

How is a KOH prep performed?

A

10-20% KOH degrades host material (no cell wall). This exposes hyphae. Calcfluor white (binds chitin) is a fluorescent stain that may be used.

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12
Q

What are pseudohyphae? How do they compare to true hyphae?

A

When yeast is budding, it elongates out; true hyphae is formed by apical extension with ‘pinching-off’ and formation of a cell wall

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13
Q

What species can classically have hyphae and pseudohyphae?

A

Candida albicans

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14
Q

What is silver stain used for?

A

Silver nitrate outlines fungi in black. May also stain some bacteria (e.g. Nocardia)

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15
Q

What is mucicarmine generally used for?

A

Cryptococcus; stains mucin

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16
Q

What is the best test to order for cryptococcus?

A

Cryptococcal antigen test (CSF or serum); should be backed up with fungal culture!!

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17
Q

What fungi do not contain beta-D-glucan in their cell walls?

A

Cryptococcus, Mucorales, and the yeast phase of dermatitidis

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18
Q

For which fungus does the (1,3)-beta-D-glucan (Fungitell) antigen assay have the greatest sensitivity and specificity?

A

Pneumocystis pneumonia

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19
Q

For Aspergillus species, which test is superior: (1,3)-beta-D-glucan (Fungitell) antigen assay or serum galactomannan?

A

About the same

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20
Q

What can cause false positives with the (1,3)-beta-D-glucan (Fungitell) antigen essay?

A

IVIG, hemodialysis membranes, surgical sponges

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21
Q

What is galactomannan?

A

A cell wall polysaccharide produced by Aspergillus, Penicillium, Paecilomyces/Purpureocillium, and Histoplasma

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22
Q

When is the galactomannan test generally used?

A

Suspected Aspergillus infection

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23
Q

What is the antigen used in the Histoplasma antigen test?

A

Galactomannan, but optimized for Histoplasma rather than Aspergillus

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24
Q

What are the two methodologies used in fungi antibody detection?

A

1) Complement fixation

2) Immunodiffusion

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25
Q

What fungi can be detected by serological testing?

A

Histoplasma, Blastomyces, Coccioides (note- all endemic)

26
Q

Blastomyces dermatitidis- Labs

A
  • Antigen test (urine, serum)
  • Culture
  • Antibody testing
27
Q

Blastomyces dermatitidis- Pathological findings

A

Broad-based budding yeast

28
Q

Blastomyces dermatitidis- Endemic locations

A

Eastern and central US

29
Q

Blastomyces dermatitidis- Presentation

A

Pulmonary infection that can disseminate to skin and bone; forms granulomatous nodules

30
Q

Cryptococcus neoformans- Pathogenesis

A

Spread by exposure to soil or pigeon droppings; hematogenous spread to meninges following inhalation

31
Q

Cryptococcus neoformans- Presentation

A

CNS infection (subacute to chronic) in AIDS patients

32
Q

Histoplasma capsulatum- Labs

A
  • Antigen test
  • Culture
  • Antibody test
33
Q

Histoplasma capsulatum- Pathological findings

A

Yeast engulfed by macrophages

34
Q

Histoplasma capsulatum- Endemic locations

A

Mississippi and Ohio River valleys

35
Q

Histoplasma capsulatum- Presentation

A

Pulmonary or disseminated (or asymptomatic)

36
Q

Histoplasma capsulatum- Exposure history

A

Bird or bat droppings (i.e. caves)

37
Q

Cryptococcus neoformans- Labs

A
  • CSF analysis (opening pressure)
  • Antigen (CSF or serum)
  • Molecular panels
  • Culture
38
Q

Coccioides immitis- Labs

A
  • Antigen test
  • Culture
  • Antibody test
39
Q

Coccioides immitis- Pathological features

A

Spherule filled with endospores

40
Q

Coccioides immitis- Endemic locations

A

Southwestern US

41
Q

Coccioides immitis- Presentation

A

Pulmonary infection; usually self-limiting but can be fatal

42
Q

Sporothrix schenkii- Labs

A

Culture

43
Q

Sporothrix schenkii- Exposure history

A

Puncture by plant material (e.g. thorns)

44
Q

Sporothrix schenkii- Pathological features

A

Cigar-shaped yeast in the heat; characteristic ‘rosettes’ of conidia at ambient temperature

45
Q

Sporothrix schenkii- Presentation

A

Chronic infection, skin lesions, lymphangitis

46
Q

Candida- Labs

A
  • Culture (may appear on routine/non-fungal cultures)
  • Molecular tests
  • (1,3)-beta-D-glucan antigen test
47
Q

Candida- Presentation

A

Cutaneous, mucocutaneous, invasive, and disseminated infections

48
Q

Candida- Pathological features

A

Presence of both hyphae and pseudohyphae

49
Q

Trichophyton- Labs

A

Culture

50
Q

Trichophyton- Pathogenesis

A

Host reaction to enzymes released by the fungus

51
Q

Trichophyton- Presentation

A

Tinea capitis, Tinea corporis, Tinea cruris, Tinea pedis, Tinea unghium

52
Q

Aspergillus fumigatus- Labs

A
  • Galactomannan antigen test
  • (1,3)-beta-D-glucan antigen test
  • Culture
  • Molecular tests
53
Q

Where can Aspergillus fumigatus be found?

A

Environmental mold; decaying organic matter

54
Q

Who is at the greatest risk for infection with Aspergillus fumigatus?

A

Neutropenic patients

55
Q

Aspergillus fumigatus- Presentation

A

Pulmonary infection, including ‘air-crescent’ sign and nodules with ground-glass halo appearance. May lead to invasive infection, toxicosis, colonization, and allergy.

56
Q

Mucorales- Labs

A
  • Culture

- Pathology

57
Q

Mucorales- Pathological features

A

Rapid growth (“lid-lifters”) makes mucormycosis a medical emergency

58
Q

Mucorales- Presentation

A

Acute (often fatal) infection caused by inhalation of environmental mold or direct inoculation. Causes rhinocerebral, pulmonary, cutaneous, and GI effects (localized or disseminated).

59
Q

Fusarium- Labs

A

Culture

60
Q

Fusarium- Presentation

A

Mycotic eye infection, sinusitis, septic arthritis, nail infection, disseminated systemic infection

STEP 1 Microbiology (22 decks)

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