Opportunistic mycoses
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Opportunistic mycoses. By. Dr. Emad AbdElhameed Morad. Lecturer of Medical Microbiology and Immunology. Cryptococcus neoformans. Morphology. Yeast cells surrounded by gelatinous capsule. Virulence factors. Capsule interferes with phagocytosis. Phenol oxidase enzyme

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Opportunistic mycoses

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Opportunistic mycoses


Dr. Emad AbdElhameed Morad

Lecturer of Medical Microbiology and Immunology

Cryptococcus neoformans


  • Yeast cells surrounded by gelatinous capsule.

Virulence factors

  • Capsule interferes with phagocytosis.

  • Phenol oxidase enzyme

    • It acts on diphenolic substrate producing melanin in the fungal cell wall.


  • It lives in soil contaminated with excreta of birds especially pigeons.

  • Infection occurs by inhalation.

  • It affects immunocompromised patients especially those with AIDS.


  • Pneumonia

  • It may spread systemically to meninges causing meningitis.

  • Skin lesions

Cryptococcal Skin lesions

Laboratory diagnosis

  • Specimen:sputum, CSF

  • Direct examination of the specimen after staining using india ink:large gelatinous capsule around budding yeast cells.

Cryptococcus on bird seed agar

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

  • 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.


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

Pneumocystis jiroveci


  • It was thought to be a protozoan but molecular studies have proven that it is a fungus.

  • Pneumocystis jiroveciis the human species and the more familiar Pneumocystis cariniiis 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.

Cyst stained by silver

Trophozoites stained by Giemsa


  • Infection occurs by inhalation.

  • It affects malnourished infants and immunocompromised patients especially AIDS patients.

  • Fungal growth is limited to above the alveolarepithelium causing frothy exudate that blocks oxygen exchange.


  • Interstitial plasma cell pneumonia.

  • Death is 100% in untreated cases.

  • Extrapulmonary infections occur in late stages of AIDS.

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


  • Trimethoprim-sulfamethoxazole is the drug of choice.

  • Pentamidine and atovaquone are alternative drugs.

Germ tube




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