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Clinical Micro > Fungi > Flashcards

Fungi Flashcards

1
Q

What are 5 features of the fungi kingdom?

A
  1. Eukaryotic
  2. Larger and more complex than bacteria
  3. Cell wall (ergosterol present)
  4. lack chlorophyl
  5. reproduce asexually or sexually
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2
Q

How are fungi classified?

A

based on structures formed during sexual reproduction

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3
Q

What class of fungi do not form sexual structures?

A

The deuteromycetes

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4
Q

Are yeasts multi or single celled?

A

single celled

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5
Q

What are chains of yeast cells called?

A

pseudohyphae

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6
Q

How do yeast reproduce?

A

By budding to form daughter cells/blastopores

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7
Q

Are yeast commensal or pathogenic?

A

there are some of both

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8
Q

Are moulds multi or single celled?

A

multicellular

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9
Q

What structures do moulds form?

A

Tubular structures called hyphae which have either cross walls (called septate) or lack cross walls (aseptate)

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10
Q

What are asexual spores formed by moulds called? what do they give rise to?

A

conidiophores giving rise to conidia

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11
Q

What are arthrospores?

A

Fragmented hyphae that form spores

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12
Q

What are dimorphic fungi?

A

fungi that can behave as either yeast or mould depending on the temperature

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13
Q

What is the temperature differential for mould vs. yeast in dimorphic fungi?

A

grow as mould at RT

Yeast at elevated temps

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14
Q

What form of dimorphic fungi is typically found in the body vs the environment?

A

mould in the environment

yeast in the body

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15
Q

Can dimorphic fungi be passed person to person?

A

no because the form in the body is yeast which doesnt produce spores

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16
Q

What tends to limit the mould form of dimorphic fungi?

A

geographical distribution

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17
Q

Where can the yeast form of dimorphic fungi sometimes be seen ?

A

stained tissue samples

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18
Q

What are 4 ways in which fungi cause disease?

A
  1. growth on body surfaces
  2. Invasion of the body
  3. Allergic reactions by the body
  4. Toxins released after ingestion
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19
Q

What fungi is often a commensal of mucous membranes in the GI tract but can rapidly colonize damaged skin

A

Candida albicans

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20
Q

the sites of Candida infections by C. albicans tend to be?

A

mucocutaneous

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21
Q

What are two common forms of candidiasis?

A

oral and vaginal

22
Q

What are 3 possible presentations of oral candidiasis?

A
  1. thrush
  2. Stomatitis: denture sore mouth
  3. Chelitis: angular erosions with pustules
23
Q

What is the vaginal presentation of candidiasis like?

A

similar to thrush

24
Q

What are 3 presentations of skin infections by Candida albicans?

A

Interigo: between toes

Diaper rash: due to ammonia from urine irritating the skin and allowing the candida in

Nail

25
Q

What are 3 systemic infections that candida are often associated with?

A
  1. Urinary tract
    - due to use of foley catheters
  2. Endocarditis
    - especially with prosthetic heart valves or IV drug use
  3. Septicemia in immunosuppressed patients
26
Q

What are two lab methods of diagnosing candida infections

A
  1. Microscopy
    - KOH or gram stain
  2. Culture
27
Q

What is an encapsulated yeast endemic to BC and found in bird droppings?

A

Cryptococcus neoformans and C. gattii

28
Q

What 2 things does infection with C. neoformans/gattii cause ?

A
  1. Pneumonia
    - subclinical
  2. Meningitis
    - chronic
29
Q

What widely distributed yeast causes pneumonia in immunosuppressed patients?

A

Pneumocystis jirovecii

30
Q

What is the closely related group of keratolytic (attack skin, hair, nails) fungi

A

Dermatophytes

31
Q

What is the pathogenesis for an infection with a dermatophyte?

A
  1. minor trauma to skin = initial infection

2. Fungal penetration balances turnover of superficial skin squamous cells

32
Q

What 2 factors predispose someone to develop a dermatophyte infection?

A
  1. Minor trauma

2. Occlusion: no drying of skin. Moisture reduces harshness of skin environment

33
Q

What are some clinical features/presentations of a dermatophyte infection?

A
  1. Red, scaly, rash with pustules (maybe)

2. Central clearing and migrating margin

34
Q

How are dermatophyte infections passes?

A

Infected skin squames that contaminate fomites

- rarely by direct contact

35
Q

What is the name given to skin infections typically caused by dermatophytes?

A

Tinea (capitis, pedis…)

36
Q

How are dermatophyte infections identified?

A
  1. culture - looking for pigment of colonies

2. growth on plates - looking for macro and microconidia

37
Q

What fungi is the cause of tinea versicolor?

A

Malassezia furfur

38
Q

What is M. furfur?

A

A widepread skin commensal that flourishes by feeding on skin fatty acids

39
Q

What is the presentation of Tinea versicolor?

A

Infection is superficial, and manifests as hyper- or hypo- pigmented lesions with itching, and occasional pustules.

40
Q

How is an infection with M. furfur often identified?

A

through microscopy - looking for the characteristic spaghetti and meatballs pattern of yeast cells

41
Q

Invasive infection causing fungi can often be divided into two groups… give some examples

A
  1. Opportunistic fungi (widely occurring)
    - Aspergillus spp., Pneumocystis jirovecii, Candida spp.
  2. Geographically defined - dimorphic fungi
    - Histoplasma capsulatum
42
Q

Where can Aspergillus fumigatus be found?

A

pretty widespread on rotting vegetation

spores are commonly present in the air

43
Q

What is an important predisposing factor to disease being caused by A. fumigatus?

A

immunosuppression

44
Q

What are 3 clinical presentations of Aspergillus fumigatus?

A
  1. Allergic bronchiopulmonary
    - Asthma-like symptoms. - Fungus grows in bronchial secretions.
  2. Fungal ball in cavities of lungs and sinuses
  3. Invasive disease
    - tissue destruction and pneumonia
45
Q

What lab techniques are used to diagnose invasive fungal infections?

A

Microscopy

  • secretions/KOH
  • histology

Culture but multiple positives may occur due to contamination

46
Q

What kind of fungus is Histoplasma capsulatum? Morphology?

A

dimorphic fungus

doesn’t actually have a capsule!

47
Q

Where is Histoplasma capsulatum found

A

Central United States, especially the Mississippi river valley and Southern States, north to Ontario, Montreal.

48
Q

How does an infection with H. capsulatum occur?

A

Spores are inhaled and germinate in the lung

49
Q

What proportion of people infected with Histoplasma capsulatum develop disease? how is it detected?

A

only a small portion

identification by serology

50
Q

What is characteristic of Histoplama capsulatum in culture?

A

Growth of cells with extensions

Clinical Micro (28 decks)

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