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CMBM Exam 4 > Mycology > Flashcards

Mycology Flashcards

1
Q

Structural components of fungi

A
  • Chitin; cell wall- polymer of N-acetyl glucosamine mannans, glucans and other complex carbohydrates
  • Ergosterol; cell membrane
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2
Q

Types of fungi

A
  • Mold: filamentous form of fungi
  • Yeast: oval-shaped, single-celled form of fungi
  • Dimorphic fungi: fungi that can grow both as a mold and as a yeast
  • Dematiaceous fungi: black or brown pigmented fungi

*phaeohyphomycosis- infections caused by dematiaceous fungi

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3
Q

Hyphae

A
  • Filaments or tubular structures of molds
  • Hyphae w/cross walls (septa) are septate; Aspergillus
  • Hyphae w/o septa are coenocytic (aseptate; nonseptate; Mucormycetes
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4
Q

Pseudohyphae

A
  • Hyphae-like structure formed by incomplete budding of yeast cells
  • Candida albicans
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5
Q

Mycelium

A
  • Mass of intertwined hyphae
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6
Q

Telemorph

A
  • Fungal form producing sexual spores
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7
Q

Anamorph

A
  • Fungal form producing asexual spores
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8
Q

Common mycoses in the US

A
  • Superficial mycoses

*Tinea versicolor; malassezia furfur- normal skin flora

  • Cutaneous mycoses

*Dermatophytes; cause ringworm, also known as tinea

*Cutaenous/ mucocutaneous candidiasis

  • Subcutaneous mycoses

*Sporotrichosis- Sporothrix schenkii

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9
Q

Gomori’s methenamine silver

A
  • Stain for clinical specimens of fungi
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10
Q

Detection of fungal infections chart

A
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11
Q

Echinocandins

A
  • Inhibotor of fungal cell wall synthesis
  • Inhibits beta-glucan synthase; cell wall beta-(1,3)-glucans are not made; forms glucan polymers in the cell wall
  • Disrupts the osmotic environment of the cell, as well as cell division and growth
  • Active against fungi where beta-(1,3)-glucans are a dominant component of the cell wall

*Candida

*Aspergillus

*Invasive candidiasis and invasive aspergillosis when amphotericin B is not effective

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12
Q

Allyamines

A
  • Inhibitor of ergosterol synthesis

*inhibits squalene epoxidase (Squalene epox. transforms squalene into lanosterol which gets transformed through a few more reactions to Ergosterol)

  • Decrease Ergosterol = Increase Squalene in the cell membrane

*squalene is toxic to the cell

  • Accumulates in skin and nails
  • Terbinafine

*oral form of terbinafine => nail infections

*topical forms => skin infection

  • Side effects- GI upset, headache
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13
Q

Azoles

A
  • Imidazoles and triazoles
  • Inhibitor of ergosterol synthesis

*inhibits lanosterol 14-alpha-demethylase

+cytochrome P-450-dependent enzyme, which converts lanosterol to ergosterol

+binds to the heme moiety of cytochrome P-450

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14
Q

Imidazole

A
  • Non-ketoconazole imidazoles- topical medications

*cutaneous and mucocutaneous candida infections and dermatophyte infections

  • Ketoconazole

*tablets, creams and shampoos

*cutaneous infections, dimorphic mycoses and cryptococcus neoformans

*side effects- nausea, vomiting, anorexia and occasionally hepatotoxicity

*interferes w/steroid hormone synthesis and some drug metabolism

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15
Q

Triazoles

A
  • Greater specificity for the fungal cytochrome P-450 enzyme than imidazoles = few side effects than ketoconazole
  • Broad spectrum of activity

*candidiasis (cutaneous and invasive), dermatophytes, endemic mycoses, Cryptococcus neoformans and Aspergillus infections

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16
Q

Fluconazole

A
  • Azole
  • Cryptococcal meningitis

*good CNS penetration

*also mucocutaneous candidiasis; coccidioidal meningitis

*used as prophylaxis in bone marrow transplants

17
Q

Itranconazole

A
  • Azole
  • Prophylaxis in neutropenic patients
  • Dermatophyte infections; onychomycosis
18
Q

Voriconazole

A
  • Azole
  • Invasive asperigillosis
  • Also candida and dimorphic fungi
19
Q

Posaconazole

A
  • Azole
  • Mucormycosis
  • Also Candida and Aspergillus
20
Q

Amphotericin B

A
  • Polyene
  • Antifungal that bind ergosterol producing ion channels; membrane becomes leaky; cell death
  • Oxidation of drug generates toxic free radicals
  • Binds cholesterol, but w/a lower affinity
  • Toxicity

*renal impairment

*loss of K+ and Mg+

*infusion reaction (fever, chills, tachypnea)

*abnormal liver function tests (occasionally)

  • Lipid formulations are less toxic

*higher doses can be used

  • Broad spectrum antifungal; used for systemic infections
21
Q

Nystatin

A
  • Same mechanism as amphotericin B
  • Not absorbed so it is not present in tissues
  • Not used for systemic infections
  • Used for cutaneous or mucocutaneous candidiasis
22
Q

Flucytosine

A
  • Inhibitor of intracellular processes
  • Enters cells via cytosine permease
  • Competes w/ uracil for RNA synthesis
  • Inhibits both RNA and DNA synthesis
  • Used for cryptococcal meningits, some Candida
  • Not used as monotherapy b/c of the pssibility of developing resistant organisms
23
Q

Candida clinical infections

A
  • Responsible for ~95% of blood stream infections
  • Hospital-acquire candidemia
  • Can infect any organ system

*especially kidney, brain, liver, skin, eye

  • Serious complication in compromised patient; often fatal
  • AIDS patients

*oral thrush or esophagitis

*recurrent vaginal candidiasis

  • Complication following:

*transplants (liver, kidney, bone marrow)

*abdominal surgery (peritonitis)

*cardiac surgery (endocarditis)

24
Q

Patient population/risk factors for Candida infections

A
  • Cellular immunodeficiency

*AIDS, chronic granulomatous disease

*neutropenic patients often given fluconazole prophylaxis

*C. glabrata seen often in ICUs b/c of widespread fluconazole use

  • Immunosuppresive treatments

*bone marrow transplate patients, leukemis patients

  • Patients w/indwelling catheters, intravenous lines or prosthetic devices
  • Patients receiving corticosteroid treatment
  • Most important risk factor for invasive candidiasis is a prolonged stay in the ICU
25
Q

Candida Infection Diagnosis

A
  • Specimens:

*tissue biopsies, sputum, CSF, blood, urine

*budding yeat cells and pseudohyphae seen microscopically

  • Positive culture from normally sterile site is significant

*blood cultures are positive in only ~40-60% of cases of candidemia

*selective chromogenic medium differentiate species by color and morphology; CHROMagar

  • Circulating candidal antigens are indicative of systemic infection

*antibody titers arent diagnostic

  • Germ tube test is used to identify C. albicans
  • Commercial test now available that looks for Beta-D-glucan

*fungitell assay- modified Limulus lysate assay

*highly sensitive, rapid diagnostic test that detects (1 => 3)- Beta-D-glucan in serum

CMBM Exam 4 (14 decks)

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