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M1 > Mycology > Flashcards

Mycology Flashcards

1
Q

Fungal capsule

A

Only present in some yeasts

-Consists of polysaccharide structure
-Function as virulence factor -adhesion; and phagocytic evasion

Cryptococcus neoformans (encapsulated yeast)

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2
Q

Fungal cell wall (molecular composition)

A

Multilayered containing polysaccharides (~90%): polyhexoses, or polyhexosamines

Polysaccharides include different combinations of chitin, chitosan, cellulose, alpha-glucans, beta-glycans, and mannan

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3
Q

Fungal cell membrane

A

Has phospholipid bilayer that contains sterols (ergosterol, zymosterol)

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4
Q

Ergosterol

A

Major sterol in some fungi that is a target for drugs - the synthesis pathway makes a good target (not made in humans)

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5
Q

Fungal dimorphism

A

Some fungi can grow as either yeast-like or mold-like (depends on environmental conditions such as substrate, temperature, pH…etc.)

Dimorphic fungi are true, frank pathogens - immune system does not need to be supressed to become infected

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6
Q

Two modes of fungal sexual reproduction

A

Homothallic: haploid nuclei form adjoining parts of the same mycelium (thallus) resulting in an oospore

Heterothallic: thalli of different “mating strains” fuse, allowing haploid nuclei from two strains to fuse and form a zygospore

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7
Q

Fungal sexual reproduction

Plasmogamy

A

Cell fusion during sexual reproduction

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7
Q

Fungal sexual reproduction

Keryogamy

A

Nuclear fusion and subsequent meiosis

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7
Q

Dermatophytes

A

Cutaneous fungal infection in the living layer of the epidermis - may involve inflammation

Etiological agenst are called dermatophytes

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8
Q

Typical portal of entry for systemic fungal infection

A

Usually the respiratory tract (inhalation, usually spores) - initial lesions typically occurs in the lung - may progress slowly resulting in suppurative lesions or granuloma

Man-to-man transmission is rare

Metastatic lesions mayu occur in any organ or in the skin due to escape of organisms from primary lesion via the lymphatics or blood

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9
Q

Fungal spores

A
  1. Conidia
  2. Sporangiospores
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10
Q

Fungal asexual reproduction

A
  1. Fragmentation of hypae
  2. Budding
  3. Spores
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11
Q

Fragmentation of hypae

A

Asexual reproduction

Vegetative hyphae breaks up into individual cells

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12
Q

Polyenes

A

Target the fungal cell membrane - target ergosterol - creates holes in membrane

Fungicidal drugs

Nystatin and amphotericin B

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13
Q

Nystatin

A

Polyene

Primarily used for treating superficial fungal infections

i.e. thrush or skin infections

Applied topically

Only effective against Candida

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14
Q

Amphotericin B

A

Broad-spectrum

Used for systemic fungal infections and administered IV or intrathecally (spinal fluid)

Tx’s
Candida
Cryptococcus

and fungi responsible for:
blastomycosis
histoplasmosis
coccidoidomycosis
aspergillosis

Eliminated by liver and has a long half-life

Significant toxicity - liver disease, renal failure (in 80%), hypokalemia, phlebitis, cardiac arrest, seizures, dysrhythmias, intraslveolar hemorrhage, blood dyscrasias (agranulcytosis, leukopenia, thrombocytopenia)

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15
Q

Azoles

MOA

A

Inhibit 14-alpha-demethylase (fungal version of cytochrome P450’s)

The enzyme is necessary for converting lanosterol into ergosterol

All azoles are potent inhibitors of CYP450 enzymes - can lead to serious drug interactions (ketoconozole - known for causing fatal liver necrosis in rare cases)

16
Q

Ketoconazole

A

Inhibits human 11-beta-hydroxylase - decreasing steroid production (including testosterone)

17
Q

DOC to Tx and prevent cryptococcal meningitis

A

Fluconazole

Also used for Candida infections and prophylaxis in high-risk Pt’s

18
Q

Azole used to Tx life-threatening infections like aspergillosis and blastomycosis

A

Itraconazole - requires acidic environment for absorption

Sometimes used to Tx onychomycosis

19
Q

First-line Tx for invasive aspergillosis

A

Voriconazole

Can cause visual disturbances

20
Q

Echinocandins

A

Work by inhibiting the synthesis of beta-1,3-D-glucan (essential component of fungal cell wall)

Given IV and only used to Tx infections caused by Candida and Aspergillus

  1. Caspofungin
  2. Micafungin
  3. Anidulafungin

Not processed by liver or kidneys-no drug interactions/toxicity

21
Q

Micafungin

A

Can cause serious allergic reactions and also lead to hemolysis and elevated bilirubin

Echinocandin

22
Q

Anidulafungin

A

Effective against azole-resistant Candida (i.e.Candida albicans, Candida krusei, and Candida glabrata)

Echinocandin

23
Q

Flucytosine

A

MOA: converted to fluorouracil by cytosine deaminase (humans don’t have) and interferes with RNA and protein synthesis by competing w/ uracil

Only combined w/ other drugs (amphotericin B or itraconazole) to Tx serious fungal infections caused by Candida or Cryptococcus

Fungal infections of CNS

Fungistatic

Side-effects: bone marrow supression and liver toxicity (fluorouracil is used as a chemotherapy drug)

24
Q

Griseofulvin

A

MOA: blocks microtubule assembly - preventing fungi from undergoing mitosis

Used to Tx dermatophyte infections such as ringworm

Reduces effectiveness of warfarin and oral contraceptives by inducing some CYP450 enzymes

Fungistatic

Side-effects: angioneurotic edema, GI bleed, and liver toxicity

25
Q

Terbinafine

A

MOA: blocks squalene epoxidase (involved in early step - coversion of squalene to lanesterol - of ergosterol synthesis)

Taken orally fo 12 wks. to Tx nail fungus (dermatophyte infections)

Is hepatotoxic

26
Q

Cyclopirox

A

MOA: chelates metal ions (inhibting enzymes that help break down peroxides)

Applied topically for nail fungus (typically lasting 12 months)

Fungostatic or -cidal depending on the organism

27
Q
A

D. It inhibits demethylation of lanosterol

Azole drugs demethylate lanosterol

27
Q
A

C. Nystatin

28
Q
A

B. Terbinafine

29
Q
A

D. Any or all

30
Q

Some fungi that cause human disease can exist in two different forms. At ambient temperature, they exist as mold-like elements with spores that can become airborne. At body temperature, they transform into yeast-like elements, which can disseminate throughout the body. Fungi with this ability are called:

A

Dimorphic fungi

Dimorphic fungi are frank pathogens

31
Q

During asexual replication, hyphal elements form “spores” from which a new fungal hyphae can be derived. Which type of spore is formed within the line of hyphal elements and is “barrel-shaped”?

A

Arthrospores

32
Q

Approximately 1.4 billion people worldwide are current infected with intestinal roundworms. Roundworms are classified as which type of human parasite?

A

Nematode

33
Q

The spectrum of which of the following drugs is limited to Candida and Aspergillus infections?

A. Amphoteracin B
B. Caspofungin
C. Fluconazole
D. Itraconazole

A

B. Caspofungin

34
Q

What is the target enzyme of terbinafine?

A

Squalene epoxidase

35
Q
A

D. Amphotericin B and fluconazole

36
Q
A

D. Fluconazole

Nystatin is only available as a powder or cream

37
Q
A

D. Changes in a gene encoding for a fungal cytochrome P-450 enzyme

14-alpha-demethylase is a fungal P450 enzyme

All azoles are fungistatic not fungicidal

38
Q
A

B. Caspofungin

Griseofulvin is only for dermatophyte infections (i.e. tinea)

39
Q
A

B. Voriconazole

Terbinafine - squalene oxidase inhibitor only used to Tx dermatophyte infections

M1 (46 decks)

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