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Mycology reading > Mycology reading > Flashcards

Mycology reading Flashcards

1
Q

What are the basic forms of fungi? Are they eukaryotic?

A

Fungi are eukaryotic organisms that exist in two basic forms: yeasts and molds.

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2
Q

What are the differences between yeasts and molds?

A 
Yeasts = single cells
Molds = long filaments of cells called hyphae. 
Yeasts = reproduce by budding(daughter cells are unequal in size)
Molds = reproduce by cell division (daughter cells are equal in size)
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3
Q

What does dimorphic mean?

A
  • Fungi can exist either as yeasts or molds, depending on the temperature.
  • Room temperature = molds
  • Body temperature = yeasts (or some other form such as a spherule).
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4
Q

What is the main difference between the cell walls of fungi vs bacteria? What are the implications of using antibacterials?

A
  • Fungal cell wall = chitin
  • Bacterial cell wall = peptidoglycan

-Antibiotics that inhibit peptidoglycan synthesis such as penicillins, cephalosporins, and vancomycin are not effective

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5
Q

What is the main difference between the cell membranes of fungi vs bacteria? What are the implications of using antibacterials/fungals?

A
  • Fungal cell membrane = ergosterol
  • Bacterial cell membrane = NO ergosterol.
  • Antibiotics that inhibit ergosterol synthesis (e.g., the azole drugs) are not effective against bacteria.
  • Amphotericin B that binds to fungal cell membranes at the site of ergosterol is not effective against bacteria.
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6
Q

What are the fungi that elicit the two different responses?

A
  • Histoplasma and Coccidioides –> granulomatous host defense response (composed of macrophages and helper T cells).
  • Aspergillus, Mucor, and Sporothrix, elicits a pyogenic response (composed of neutrophils).
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7
Q

How can Histoplasma and Coccidioides be detected?

A
  • Skin tests
  • An antigen extracted (C. albicans) from the organism is injected intradermally to elicits a delayed hypersensitivity reaction, manifested as induration (thickening) of the skin.
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8
Q

What is the limitations of a skin test?

A
  • A positive skin test only indicates that infection has occurred, but it is not known whether that infection occurred in the past or at the present time.
  • A false-negative skin test can occur in patients with reduced cell-mediated immunity, such as those with a low CD4 count.
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9
Q

What predispositions cause symptoms?

A
  • Reduced cell-mediated immunity: predisposes to disseminated disease caused by the systemic fungi, such as Histoplasma and Coccidioides,
  • Reduced number of neutrophils predisposes to disseminated disease caused by fungi such as Aspergillus and Mucor.
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10
Q

What can happen if you ingest Amanita mushrooms?

A
  • Causes liver necrosis due to two fungal toxins…
  • Amanitin
  • Phalloidin
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11
Q

What does amanitin do and where is it found?

A
  • Inhibits the RNA polymerase that synthesizes cellular mRNA.
  • Toxin in Amanita mushrooms
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12
Q

What fungus can be found in peanuts and grains?

A

-A. flavus

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13
Q

What does A. flavus cause?

A

-Liver cancer due to the presence of aflatoxin.

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14
Q

What toxin is found in A. flavus and what does it do?

A

-Aflatoxin epoxide –> induces a mutation in the p53 gene that results in a loss of the p53 tumor suppressor protein.

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15
Q

What can be caused by inhalation of the spores of Aspergillus fumigatus?

A

-Can cause allergic bronchopulmonary aspergillosis. This is an IgE-mediated immediate hypersensitivity response.

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16
Q

What are the four approaches to the laboratory diagnosis of fungal diseases?

A

(1) direct microscopic examination, (2) culture of the organism, (3) DNA probe tests, and (4) serologic tests.

17
Q

Describe (1) direct microscopic examination.

A
  • A 10% potassium hydroxide (KOH) preparation can reveal the presence of fungal structures. |
  • The purpose of the KOH is to dissolve the human cells, allowing visualization of the fungi.
18
Q

Describe (2) culture of the organism.

A

Sabouraud’s agar is often used to grow fungi because its low pH inhibits the growth of bacteria, allowing the slower-growing fungi to emerge.

19
Q

Describe (3) DNA probe tests.

A

DNA probes can be used to identify fungi growing in culture at a much earlier stage (i.e., when the colony size is much smaller).

20
Q

Describe (4) serologic tests.

A

Tests for the presence of fungal antigens and for the presence of antibodies to fungal antigens are often used. Two commonly used tests are those for cryptococcal antigen in spinal fluid and for Coccidioides antibodies in the patient’s serum.

21
Q

What do amphotericin B and the azole group of drugs attack?

A

-Presence of ergosterol in fungal cell membranes

22
Q

Where does amphotericin B bind?

A

-Binds to fungal cell membranes at the site of ergosterol and disrupts the integrity of the membranes.

23
Q

What are some examples of azole drugs and what do they do?

A

-Itraconazole, fluconazole, and ketoconazole: Inhibit the synthesis of ergosterol.

24
Q

What do echinocandins group of drugs attack?

A

-Based on the presence of a cell wall in fungi, Echinocandins inhibit the synthesis of d-glucan, which is a component of the fungal cell wall. caspofungin

25
Q

What is an example of echinocandin drugs and what do they do?

A
  • Caspofungin

- Inhibit the synthesis of d-glucan, which is a component of the fungal cell wall.

26
Q

What are the four divisions of medical mycoses

A

(1) cutaneous, (2) subcutaneous, (3) systemic, and (4) opportunistic

27
Q

What is infected by (1) cutaneous mycoses?

A

Superficial keratinized structures

28
Q

What is infected by (2) subcutaneous mycoses?

A

In human tissue

29
Q

What causes (3) systemic mycoses infection?

A

Inhalation of the spores of dimorphic fungi (mold in soil). Within the lungs, the spores differentiate into yeasts or other specialized forms, such as spherules.

30
Q

Describe (3) systemic mycoses infections?

A

Most lung infections are asymptomatic and self-limited. However, in some persons, disseminated disease develops in which the organisms grow in other organs, cause destructive lesions, and may result in death. Infected persons DO NOT COMMUNICATE these diseases to others.

31
Q

What is another name for (3) systemic mycoses infections?

A

Endemic fungi because they are endemic (localized) to certain geographic areas.

32
Q

Describe (4) opportunistic mycoses infections?

A
  • They fail to induce disease in most immunocompetent persons but can do so in those with impaired host defenses.
  • There are five genera of medically important fungi: Candida, Cryptococcus, Aspergillus, Mucor, and Rhizopus.

Mycology reading (1 decks)

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