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Foundations Exam 3 > Fungi > Flashcards

Fungi Flashcards

1
Q

what does it mean that fungi are saprophytic?

A

secrete digestive enzymes which break down dead organic matter for nourishment (cellulase, protease, nuclease)

habitat is soil or water

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2
Q

what kind of pathogen does this describe?
- thick, rigid wall
- potent immunogenic
- main immunity is via neutrophils (phagocytosis)
- some considered normal flora

A

fungi

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3
Q

what are 3 unique things about the fungi cell wall that are possible drug therapies?

A
  1. chitin (fibrous)
  2. mannoproteins
  3. glucans (glucose polymers)

TLR bind fungal cell wall components

*antibiotics against peptidoglycan will be useless

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4
Q

what do fungi have in their cell membrane that is different than mammalian cell membranes, and can be targeted by drug therapy?

A

ergosterol (instead of cholesterol)

*note ergosterol is similar to cholesterol, so drugs targeting this will have toxic side effects

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5
Q

what are the 2 types of fungi morphology?

A

molds (filamentous fungi): cells elongate to form hyphae

yeast: unicellular, reproduce by budding

most fungi are dimorphic (typically mold culture at lower temp, yeast in tissues at higher temp)

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6
Q

what is a mass of fungi hyphae?

A

mycelium (pleural is mycelia)

grow by cytoplasmic extension and branching, mitotic division without cell division/separation

large fuzzy colonies in culture, usually pigmented

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7
Q

dimorphic fungi usually cause what level of infection?

A

usually systemic mycoses

filamentous mold at lower temp (culture), unicellular yeast at higher/body temp (tissue)

can also change forms based on environmental conditions

ex: Blastomyces dermatiditis, Histoplasma capsulatum

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8
Q

explain the basic principles of the fungi life cycle (what are the two forms of reproduction)

A

fungi can live as haploids or diploids, spores can reproduce and spread in environment:

fusion of haploid spores (mitotic) —> results in diploid asexual spores

sporulation of diploid spores (meiosis) —> haploid sexual spores

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9
Q

[sexual/asexual] fungi spores are rarely seen in clinical samples (rare among human pathogens)

A

sexual fungi spores are rarely seen in clinical samples (rare among human pathogens)

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10
Q

characteristic shape and pattern of _____, where sexual fungi spore meiosis occurs, serves as primary means of species classification

A

ascus (spore sac, where meiotic spores are formed)

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11
Q

clinical identification of fungi is by [sexual/asexual] reproduction

A

clinical identification of fungi is by asexual reproduction

remember that asexual spores are produced by mitosis

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12
Q

conidia are what kind of fungal spore?

A

conidia: asexual spores made outside specialized cells

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13
Q

sporangiosphores

A

sporangioshpores: asexual fungal spores made within specialized sac (sporangium)

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14
Q

what is the typical agar that fungi are cultured on?

A

Saboraud agar: broth + glucose, low pH inhibits bacteria (also antibiotics)

*note that fungi are NOT fastidious and grow best at 30C

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15
Q

when growing fungi on Saboraud agar, what are dematiaceous vs hyaline colonies?

A

dematiaceous = pigmented
hyaline = colorless

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16
Q

what is typically added to fungal stains, and what are 2 stains that can be used?

A

KOH added (kills mammalian cells, but fungi walls are resistant)

  1. Calcofluor white staining: fluorescent dye bind polysaccharide in fungal walls
  2. Methenamine silver (Grocott’s) stain: shows fungi in tissue sections
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17
Q

What kind of mycoses is caused by Aspergillus fumigatus?
a. superficial
b. cutaneous
c. subcutaneous
d. systemic
e. opportunistic

A

opportunistic

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18
Q

What kind of mycoses is caused by Histoplasma?
a. superficial
b. cutaneous
c. subcutaneous
d. systemic
e. opportunistic

A

systemic

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19
Q

What kind of mycoses is caused by Blastomyces?
a. superficial
b. cutaneous
c. subcutaneous
d. systemic
e. opportunistic

A

systemic

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20
Q

What kind of mycoses is caused by Coccidiodes?
a. superficial
b. cutaneous
c. subcutaneous
d. systemic
e. opportunistic

A

systemic

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21
Q

What kind of mycoses is caused by Pneumocystis jirovecci?
a. superficial
b. cutaneous
c. subcutaneous
d. systemic
e. opportunistic

A

opportunistic

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22
Q

What kind of mycoses is caused by Candida albicans?
a. superficial
b. cutaneous
c. subcutaneous
d. systemic
e. opportunistic

A

opportunistic

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23
Q

What kind of mycoses is caused by Sporothrix schenkii?
a. superficial
b. cutaneous
c. subcutaneous
d. systemic
e. opportunistic

A

subcutaneous

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24
Q

pityriasis versicolor

A

superficial mycoses, scaly patches of discolored skin (torso, upper arms)

yeast eating keratin in skin

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25
Q

piedra

A

superficial mycoses, fungal growth on hair shafts (eating keratin)

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26
Q

pityriasis versicolor vs piedra

A

both superficial mycoses, fungi eating keratin

pityriasis versicolor - skin
piedra - hair shafts

27
Q

what kind of fungi cause cutaneous mycoses?

A

dermatophytes - cause lesions with inflamed rim of active infection and central clearing of healing

found everywhere, can be infectious, distinguished by micro- and macro-conidia morphology

28
Q

tinia

A

fungal infection of keratinized tissue

distinguished by where they are found on body (ex: Tinea pedis = athlete’s foot)

29
Q

what mycoses does Sporothrix schenkii cause?

A

Sporotrichosis (“Rose Gardener’s Disease”): subcutaneous mycoses, puncture becomes granulomatous, usually self-limiting (systemic in immunocompromised)

secondary lesions along draining lymphatics

*note Sporothrix schenckii is dimorphic - yeast form in tissue

30
Q

mycetoma

A

subcutaneous mycoses, subcutaneous mass of fungi surrounded by granulomatous inflammation

31
Q

how are systemic mycoses usually caused (acquired)?

A

spores inhaled from soil into lungs, can disseminate

*usually asymptomatic, except for in immunocompromised, children, elderly

32
Q

where (geographically) and from what is Histoplasma capsulatum usually acquired?

A

central US: Ohio and Mississippi River Valleys

via spores in soil with bird droppings, conidia inhaled

33
Q

how does Histoplasma capsulatum (causes systemic mycoses) proliferate in the body? what kind of immunity is required?

A

intracellular - multiply within macrophages

requires cell mediated immune response - granulomas form

34
Q

what kind of illness does Histoplasma capsulatum cause?

A

systemic mycoses, usually asymptotic

otherwise acute/self-limited pulmonary illness, can present like TB

(recall Histoplasma acquired from spores in soil with bird droppings)

35
Q

where (geographically) and from what is Blastomyces dermatitidis usually acquired?

A

Eastern US + north to Canada

microconidia in soil inhaled, but rarely disseminates from lungs

36
Q

what kind of illness does Blastomyces dermatitidis cause?

A

about half have symptoms - fever/cough/muscle aches/chest pain/fatigue

rarely disseminates from lungs, but if so, forms ulcerated granulomas (skin, bone, GU)

37
Q

how does Blastomyces dermatitidis germinate in the body?

A

germinate into thick wall yeast cells with unipolar broad based buds - very important for identifying in microscopy

Blastomyces - Broad Bases Buds

38
Q

where (geographically) is Coccidioides immitis usually acquired, and how does it germinate in the body?

A

SouthWest US, Central and South America

germinate into large spherules filled with many spores, which rupture to release endospores

endospores disseminate and form new spherules

39
Q

what kind of mycoses does Coccidioides immitis cause?

A

“Valley Fever”: fever with variable respiratory illness

if spores spread to CNS —> meningitis

usually self-limiting

40
Q

what type of fungus forms yeast in infected tissue or exudates that resembles a ship steering wheel, made of multiple buds?

A

Paracoccidioides

41
Q

Where (geographically) is paracoccidioides mycoses acquired, who is affected, and what illness does it cause?

A

Central and South America - mature males only (inhibited by estrogen)

causes respiratory illness, with most common secondary site being mucosa of mouth and nose —> painful/destructive lesions

42
Q

what kind of mycoses do Aspergillus fumigatus, Pneumocystis jirovecci, Candida albicans, Cryptococcus neoformans, and Zygomyces cause?

A

opportunistic mycoses

43
Q

where does Candida albicans come from and what kind of mycoses does it cause?

A

Candida albicans: normal flora of mucous membranes (respiratory, GI, female genital)

causes opportunistic mycoses (Candidiasis) when normal bacterial flora is diminished

*most common nosocomial pathogen

44
Q

describe the clinical features of Candidiasis, caused by nosocomial Candida albicans?

A

invasive candidiasis enters bloodstream and disseminates, forms budding yeast and pseudohyphae in tissue and culture

—> oral thrush (raised white plaque, ulcer spreads to throat), vaginal candidiasis (white discharge, itch/burn), forms biofilm

*often sign of compromised cell mediated immunity, such as in AIDS

45
Q

what is the function of the biofilm produced by Candida albicans?

A

Candida albicans: most common nosocomial pathogen

biofilm protects yeast from immune system/anti-fungal drugs

attaches to surfaces (human tissue, medical devices)

46
Q

Germ Tube Test

A

screening test to differentiate Candida albicans

grow specimen in serum and germ tube forms (filamentous growth from cells, looks like a worm)

47
Q

what fungi does this describe?
- found in soil containing bird droppings
- THICK polysaccharide capsule surrounding budding yeast cell
- infections start in lung, spread to brain/meninges
- opportunistic but can affect both immunocompromised and healthy patients

A

Cryptococcus: found in soil containing bird droppings, thick polysaccharide capsule, can spread to brain/meninges

48
Q

what fungi does this describe?
- ubiquitous in environment
- only mold form
- 45* angle branching hyphae with septa
- pulmonary infection can produce fungus ball (mass of hyphae) in lung

A

Aspergillus: only mold form, form 45 degree branching hyphae with septa

aspergilloma: mass of hyphae in lung cavity

acute aspergillosis can be severe for immunocompromised (rarely infects healthy patients) - opportunistic

49
Q

what fungi does this describe?
- ubiquitous, most adults have Ab
- causes pneumonia, NOT self-limiting (fatal if untreated)
- opportunistic via activation of dormant cysts in lungs
- cannot culture in lab
- no ergosterol in membrane

A

Pneumocystis jiroveci/carinii: causes Pneumocystis pneumonia (PcP or PjP) via activation of dormant cysts in lungs

—> alveoli inflammation, body produces exudate that blocks gas exchange (damage via body’s mechanisms)

50
Q

how do polyenes work?

A

anti-fungal drugs that form pores/channels in cell membrane

ex: Amphotericin B (systemic, IV), Nystatin (topical, toxic)

51
Q

what class of anti-fungal drugs form pores in the cell membrane?

A

Polyenes

ex: Amphotericin B (systemic), Nystatin (topical)

52
Q

how do azoles work?

A

anti-fungal drugs that inhibit cytochrome P450-dependent enzymes involved in ergosterol biosynthesis

loss of ergosterol —> loss of membrane integrity

ex: Fluconazole, Itraconazole, Ketoconazole

*recall that ergosterol is similar to cholesterol, which is in human cell membranes, so long term use of azoles is toxic (liver toxicity)

53
Q

why can’t azoles be administered long-term?

A

azoles: inhibit cytochrome P450-dependent enzymes involved in ergosterol biosynthesis

ergosterol is similar to cholesterol, which is in human cell membranes, so long term use of azoles is toxic (liver toxicity)

54
Q

what kind of drugs are Amphotericin B and Nystatin, and what do they target?

A

polyenes: anti-fungal, form pores in cell membrane

Amphotericin - systemic, IV
Nystatin - topical

55
Q

what kind of drugs are Fluconazole, Itraconazole, and Ketoconazole, and what do they target?

A

Azoles: anti-fungal, inhibit ergosterol biosynthesis

(inhibit cytochrome P450-dependent enzymes involved in ergosterol biosynthesis)

*note liver toxicity with long-term use, because ergosterol is similar to cholesterol (in human cell membranes)

56
Q

what does Caspofungin do?

A

anti-fungal drug, inhibits glucan synthesis (disrupts cell wall)

57
Q

what does 5-Fluorocytosine do?

A

anti-fungal drug, inhibits DNA and RNA synthesis (not used alone)

58
Q

colonies that grow hyphae branching at 45* angles belong to what genus?

A

Aspergillus

59
Q

pt is 32yo F presenting with creamy white patches lining her oral cavity. Culture from a scraping reveals budding yeast and pseudohyphae, which when suspended in plasma appear as buds with thin streaks extending from them. What fungus is this?

A

Candida albicans (Germ Tube Test)

60
Q

pt presents with slowly-developing pneumonia and lung opacities revealed in x-ray. Stained smear of leukocytes show many tiny intracellular yeast form inclusions. What organism is this most likely to be?

A

Histoplasma capsulatum - tiny intracellular yeast forms in tissue, hyphae with macroconidia in culture

61
Q

pt presents with pneumonia, and bronchoalveolar fluid recovered contains cysts with ring forms. What organism is likely the cause of pneumonia?

A

Pneumocystis carinii (P. jirovecci) - yeast, cyst in lungs

pneumonia in immunocompromised hosts

62
Q

what causes Valley Fever (fever with respiratory illness)?

A

Coccidioides immitis - found in desert soil of SW USA

tissue morphology: large spherules with multiple endospores

culture morphology: anthroconidia (tubes)

63
Q

pt is 57yo M with history of chemotherapy presenting with headache and stiff neck. CSF is centrifuged and the pellet is stained with India Ink, which reveals encapsulated yeast. What is it?

A

Cryptococcus neoformans: heavily encapsulated, from soil/bird droppings, lung infection that spreads to brain/meninges

64
Q

what fungus is found in soil of Central & South America and causes pulmonary infections that can disseminate to mucosal mouth and nose?

A

Paracoccidoides braziliensis

tissue morphology: large yeast with multiple buds (“steering wheel”)

no culture morphology

Foundations Exam 3 (28 decks)

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