Opportunistic mycoses

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Opportunistic mycoses
By
Dr. Emad AbdElhameed Morad
Lecturer of Medical Microbiology and Immunology
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Cryptococcus neoformans
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Morphology

• Yeast cells surrounded by gelatinous capsule.

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Virulence factors

• Capsule interferes with phagocytosis.
• Phenol oxidase enzyme
• It acts on diphenolic substrate producing
  melanin in the fungal cell wall.

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Pathogenesis

• It lives in soil contaminated with excreta of
  birds especially pigeons.
• Infection occurs by inhalation.
• It affects immunocompromised patients especially
  those with AIDS.

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Diseases

• Pneumonia
• It may spread systemically to meninges causing
  meningitis.
• Skin lesions

Cryptococcal Skin lesions
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Laboratory diagnosis

• Specimen sputum, CSF
• Direct examination of the specimen after
  staining using india ink large gelatinous
  capsule around budding yeast cells.

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• Culture on SDA or bird seed agar at 25 37
  degree.

Cryptococcus on bird seed agar
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• Identification of cryptococcus on the plate is
  done by
• Morphology mucoid colonies. It appears brown to
  black on bird seed agar.
• India ink staining
• Biochemical reactions urease positive phenol
  oxidase positive.
• DNA probes
• Direct detection of capsular antigen in CSF by
  latex agglutination test.

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Treatment

• Amphotericin B and flucytosine are given for 6
  months. Given for life with AIDS patients.

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Pneumocystis jiroveci
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Morphology

• It was thought to be a protozoan but molecular
  studies have proven that it is a fungus.
• Pneumocystis jiroveci is the human species and
  the more familiar Pneumocystis carinii is found
  only in rats.
• It has two distinct forms
• Thick walled cyst which contain 4 8 nuclei. The
  cyst wall is stained by silver.
• Thin walled trophozoites which are stained by
  Giemsa.

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Cyst stained by silver
Trophozoites stained by Giemsa
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Pathogenesis

• Infection occurs by inhalation.
• It affects malnourished infants and
  immunocompromised patients especially AIDS
  patients.
• Fungal growth is limited to above the alveolar
  epithelium causing frothy exudate that blocks
  oxygen exchange.

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Diseases

• Interstitial plasma cell pneumonia.
• Death is 100 in untreated cases.
• Extrapulmonary infections occur in late stages
  of AIDS.

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Laboratory diagnosis

• Specimen bronchoalveolar lavage, induced sputum
  or lung biopsy.
• Direct examination of the specimen after
  staining using
• Silver to stain cyst wall
• Giemsa to stain trophozoites
• Direct IF or PCR

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Treatment

• Trimethoprim-sulfamethoxazole is the drug of
  choice.
• Pentamidine and atovaquone are alternative
  drugs.

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Germ tube
Chlamydospores
CHROMagar
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GOOD LUCK