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mycology Flashcards

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1
Q

Discuss the characteristics of molds

A
  • multicellular ,filamentous
  • basic structural unit is a chain of multinucleate tubular cells called hypha
  • reproduce through production of spores (conidia )
  • hyphae stain gram negative
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2
Q

Discuss the dermatophyte epidemiology

A
  • infections of the skin
  • use communal bathing facilities - tinea pedis
  • in young children manifests as tinea capitis(ring worm)
  • caused by groups closely related moulds
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3
Q

Discuss the

pathogenesis of dermatophyte

A

*Source may be animals , human or soil
*Spread by direct or indirect contact
*Typical lesions
-annular scaling patch with raised inflamed margin
due to direct tissue damage by fungus and immune response

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4
Q

Discuss the epidemiology of mucormycosis

A
  • Most cases caused by rhizopus ,mucor ,lichtheimia or rhizomucor species
  • These saprophytic moulds are ubiquitous ( they are found in soil and decaying matter)
  • Opportunistic infection occurring in specific patient populations
  • poorly controlled diabetes mellitus ( ketoacidosis )
  • Prolonged neutropenia

*Cutaneous disease may occur in normal host following traumatic inoculation

*

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5
Q

Discuss the mucormycosis pathogenesis

A
  • Infection may follow inhalation or cutaneous inoculation
  • Angioinvasive moulds
  • innate immunity (phagocytosis to prevent spore or conidia germination and killing of hyphal forms) is important
  • Invasion of blood vessels with thrombosis and infarction of tissue
  • Aggressive infection
  • acute onset and rapid relentless progression

*Hallmark of mucormycosis

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6
Q

Discuss the epidemiology of aspergillus

A

*ubiquitous
found in air ,soil ,decaying organic matter

*Cause both invasive and non-invasive infections
*invasive infections occur in immuno suppressed patients
-hematological malignancy ,transplant
patients on corticosteroids or other immune suppression

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7
Q

Discuss the pathology of aspergillus

A
  • Infection may follow inhalation of fungal spores / conidia
  • Hall mark of invasive infection is vascular invasion and infarction
  • -In the absence of effective defense ( polymorpholic neutrophiles and macrophages connidia germinates and hyphae invade vasculature

*Infection in immunocompromised host ( due to prolonged neutropaenia)
it is often invasive in pulmonary , sinusitis and cerebral

*Infection associated with tissue damage and foreign body

  • Infection in otherwise healthy host
  • allergic
  • toxin-mediated
  • superficial or non-invasive
  • invasive
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8
Q

Discuss the characteristics of dimorphic fungi

A
  • Capable of changing growth to either mycelial (mould) or yeast phase ,depending on growth conditions
  • Mould in natural environment (25 degrees Celsius ) and yeast in tissue ( 37 degrees celsius)
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9
Q

Medically important medical fungi

A
  1. Histoplasma capsulatum
    * sporothrix schenckii
    * blastmyces dermatitidis
    * emergomyces africanus
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10
Q

Discuss the epidemiology of histoplasmosis

A
  • Histoplasma capsulatum is dimorphic and is a soil based fungus ( from birds and bats droppings)
  • Found in many regions of the word
  • Immunosuppressed persons and may develop disseminated disease
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11
Q

Discuss the histoplasma pathogenesis

A

1Histoplasma capsulated spores are inhaled
2.spores enter the lungs and travel to alveolar spaces where the immune cells trap them

3.Immune cells transport spores through the lymph system to mediastinal lymph nodes where they multiply and if not eliminated ,enter blood stream and spread through the body

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12
Q

Discuss the epidemiology of sporotrichosis

A

*sporotrichosis schenkii
is isolated from soil and plants
*Scratches on exposed skin give rise to initial lesion
-can spread along proximal lymphatics

  • extracutaneous spread may occur
  • in advanced HIV disseminated often occur
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13
Q

How can sporotrichosis be treated

A

foe lyphocutaneous form can be treated with itraconazole and in desseminated disease,IV apmhotericin B

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14
Q

How can Histoplasmosis be treated

A
  • IV amphotericin B for disseminated forms

* itraconazole in non immunocompromised patients

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15
Q

Discuss the general characteristics of fungi

A
  • They are eukaryotic
  • Rigid cell wall
  • require preformed organic compounds for their nutrients
  • some are pathogenic ,others are environmental saprobes (live of dead organic matter )
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16
Q

Fungi are divided into 2 to groups based on morphology .

A
  1. Yeasts
    * unicellular and round in shape
    * multiply by budding
    * strain gram pos
  2. Moulds
    * multicellular filamentous
    * reproduce through spore production
    * hyphae stain gram eg
  3. Dimorphic fungi
    * Capable of changing their growth to either mycelial moulds or yeast
17
Q

Discuss the epidemiology of fungi

A
  1. Most infections caused by fungi that grow as saprophytes in the enviroment
    - infections result from
    * Inhalation
    * ingestion
    * traumatic inoculation
  • Some yeast are commensals that may cause endogenous infection when there is disruption of normal host defenses
    3. Dermaphytes that cause skin , hair, nails infections are transmissible from person to person
18
Q

Describe the candida morphology

A

oval to round yeasts

  • colonies have a creamy texture
  • white and cream coloured colonies
19
Q

Discuss the candida pathogen

A

*Some virulence factors but only modest capacity to invade

  • Infection is associated with diruption of normal flora (microbiota) or normal host defence
  • natural
  • diabetes mellitus
  • low birth weight neonates

*iatrogenic (complications resulting from medical care)
*broad spectrum antimicrobial
-central venous lines
-immunosuppressive
-prolonged stay at ICU
-abdominal surgery
-

20
Q

Discuss the morphology of cryptococcus

A

*round yeasts
*polysaccharide capsule
(capsule appears as clear halo around organism when stained by india ink stain
*Mucoid colonies

21
Q

Discuss the cryptococcus epidemiology

A
  • cryptococcus neoformans are found in pigeon dropping
  • common cause of meningitis in aids patients
  • In SA, Cryptococcus neoformans is the most commonly detected pathogen
22
Q

Discuss the cryptococcus pathogenesis

A
  • Virulence factors include :
  • anti- phagocytic capsule ,melanin, lytic enzymes
  • Infection is aquired by inhalation
  • alveolar macrophage elicit Th1 response
  • In immunosuppressed host ,yeast continues to proliferate and disseminate
  • Cryptococcu neoformans is associated with infections in persons with T cell abnormalities and o corticosteriod therapy
  • It is a aids defining illness

Microbiology (13 decks)

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