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Foundations Exam 3 > Fungi > Flashcards

Fungi Flashcards

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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
piedra
superficial mycoses, fungal growth on hair shafts (eating keratin)
26
pityriasis versicolor vs piedra
both superficial mycoses, fungi eating keratin pityriasis versicolor - skin piedra - hair shafts
27
what kind of fungi cause cutaneous mycoses?
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
tinia
fungal infection of keratinized tissue distinguished by where they are found on body (ex: Tinea pedis = athlete’s foot)
29
what mycoses does *Sporothrix schenkii* cause?
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
mycetoma
subcutaneous mycoses, subcutaneous mass of fungi surrounded by granulomatous inflammation
31
how are systemic mycoses usually caused (acquired)?
spores inhaled from soil into lungs, can disseminate *usually asymptomatic, except for in immunocompromised, children, elderly
32
where (geographically) and from what is *Histoplasma capsulatum* usually acquired?
central US: Ohio and Mississippi River Valleys via spores in soil with bird droppings, conidia inhaled
33
how does *Histoplasma capsulatum* (causes systemic mycoses) proliferate in the body? what kind of immunity is required?
intracellular - multiply within macrophages requires cell mediated immune response - granulomas form
34
what kind of illness does *Histoplasma capsulatum* cause?
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
where (geographically) and from what is *Blastomyces dermatitidis* usually acquired?
Eastern US + north to Canada microconidia in soil inhaled, but rarely disseminates from lungs
36
what kind of illness does *Blastomyces dermatitidis* cause?
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
how does *Blastomyces dermatitidis* germinate in the body?
germinate into thick wall yeast cells with unipolar *broad based buds* - very important for identifying in microscopy *Blastomyces - Broad Bases Buds*
38
where (geographically) is *Coccidioides immitis* usually acquired, and how does it germinate in the body?
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
what kind of mycoses does *Coccidioides immitis* cause?
“Valley Fever”: fever with variable respiratory illness if spores spread to CNS —> meningitis usually self-limiting
40
what type of fungus forms yeast in infected tissue or exudates that resembles a ship steering wheel, made of multiple buds?
Paracoccidioides
41
Where (geographically) is paracoccidioides mycoses acquired, who is affected, and what illness does it cause?
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
what kind of mycoses do *Aspergillus fumigatus*, *Pneumocystis jirovecci*, *Candida albicans*, Cryptococcus neoformans, and Zygomyces cause?
opportunistic mycoses
43
where does *Candida albicans* come from and what kind of mycoses does it cause?
*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
describe the clinical features of Candidiasis, caused by nosocomial *Candida albicans*?
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
what is the function of the biofilm produced by *Candida albicans*?
*Candida albicans*: most common nosocomial pathogen biofilm protects yeast from immune system/anti-fungal drugs attaches to surfaces (human tissue, medical devices)
46
Germ Tube Test
screening test to differentiate *Candida albicans* grow specimen in serum and germ tube forms (filamentous growth from cells, looks like a worm)
47
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
Cryptococcus: found in soil containing bird droppings, *thick polysaccharide capsule*, can spread to *brain/meninges*
48
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
*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
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
*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
how do polyenes work?
anti-fungal drugs that form pores/channels in cell membrane ex: Amphotericin B (systemic, IV), Nystatin (topical, toxic)
51
what class of anti-fungal drugs form pores in the cell membrane?
Polyenes ex: Amphotericin B (systemic), Nystatin (topical)
52
how do azoles work?
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
why can’t azoles be administered long-term?
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
what kind of drugs are Amphotericin B and Nystatin, and what do they target?
polyenes: anti-fungal, form pores in cell membrane Amphotericin - systemic, IV Nystatin - topical
55
what kind of drugs are Fluconazole, Itraconazole, and Ketoconazole, and what do they target?
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
what does Caspofungin do?
anti-fungal drug, inhibits glucan synthesis (disrupts cell wall)
57
what does 5-Fluorocytosine do?
anti-fungal drug, inhibits DNA and RNA synthesis (not used alone)
58
colonies that grow hyphae branching at 45* angles belong to what genus?
*Aspergillus*
59
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?
*Candida albicans* (Germ Tube Test)
60
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?
*Histoplasma capsulatum* - tiny intracellular yeast forms in tissue, hyphae with macroconidia in culture
61
pt presents with pneumonia, and bronchoalveolar fluid recovered contains cysts with ring forms. What organism is likely the cause of pneumonia?
*Pneumocystis carinii (P. jirovecci)* - yeast, cyst in lungs *pneumonia in immunocompromised hosts*
62
what causes Valley Fever (fever with respiratory illness)?
*Coccidioides immitis* - found in desert soil of SW USA tissue morphology: large spherules with multiple endospores culture morphology: anthroconidia (tubes)
63
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?
*Cryptococcus neoformans*: heavily encapsulated, from soil/bird droppings, lung infection that spreads to brain/meninges
64
what fungus is found in soil of Central & South America and causes pulmonary infections that can disseminate to mucosal mouth and nose?
*Paracoccidoides braziliensis* tissue morphology: large yeast with multiple buds (“steering wheel”) no culture morphology

Foundations Exam 3 (28 decks)

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