Mycology Systemic Dimorphic Fungi Division of Medical Technology Carol Larson MSEd, MT(ASCP) Please...

MycologySystemic Dimorphic Fungi

Division of Medical Technology

Carol Larson MSEd, MT(ASCP)

Please click audio iconto hear Carol’s narration

General Characteristics

• Growth rate: 2-4 weeks

• Identification– Direct specimen examination– Colony morphology– Microscopic morphology– Definitive diagnosis is prove dimorphism

• Mycelial stage at 25-30ºC• Yeast / spherule stage in host at 35-37ºC

Click icon for audioSystemic Dimorphic Fungi

Epidemiology

• Primarily in North America or South America

• Found in:– Soil– Decaying vegetation– Bird droppings– Bat droppings


Clinical Significance

• Pathogens

• Man incidental host

• Acquire by inhalation

• Develop respiratory infection

• Can disseminate and become systemic infection


Clinical Significance

• Histoplasmosis– Histoplasma capsulatum

• Blastomycosis– Blastomyces dermatitidis

• Coccidioidomycosis– Coccidioides immitis

• Paracoccidioimycosis– Paracoccidioides brasiliensis


For the systemic dimorphic fungi, what must be demonstrated in the lab to definitively identify them?

The systemic dimorphic fungi have two forms (mold and yeast/spherule) and both must be seen in the laboratory either in culture or in direct examination of a specimen.

How are the systemic dimorphic fungal infections acquired?

By inhalation of the conidia and fungal elements. The infection begins in the lungs for all of the systemic dimorphic fungi.

Histoplasmosis

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• Histoplasma capsulatum

• Pathogenesis– 95% of cases are asymptomatic– Infection begins in lung– Invades reticuloendothelial system– Can disseminate (especially in

immunocompromised patients)

Laboratory Diagnosis

• Specimen– Sputum– Blood– Bone marrow– Urine– Oral lesion scraping– Lymph node biopsy– Liver

Click icon for audioHistoplasmosis


• Direct detection methods– Giemsa or Wright’s stains– Calcofluor white stain, histological stains– Look for small intracellular yeast cells


Mold - Histoplasma capsulatum


• Media– Sab’s and Inhibitory Mold agars

• Good growth at 2-4 weeks

– Mycosel agar – no growth

• Incubate– 25-30ºC– Ambient air– Up to 4-6 weeks


• Colony morphology



• Microscopic morphology


Yeast - Histoplasma capsulatum

• Media– Blood enriched media– Incubate at 35ºC in ambient air for 2-4 weeks


• Microscopicmorphology


Serological Testing

• Exoantigen test– Immunodiffusion


What is the diagnostic form for Histoplasma capsulatum and what does it look like?

The mold phase – its macroconidia are large, round, unicellular, thick-walled and tuberculated.

In patient specimens, where is a common place that you would find Histoplasma capsulatum yeast?

Histoplasma capsulatum yeast cells are often found intracellular in mono-nucleated cells.

Blastomycosis


• Blastomyces dermatitidis

• Pathogenesis– Acute or chronic suppurative and

granulomatous infection– Infection begins in lung– Can disseminate to lungs, bone, soft

tissue and skin


• Specimen– Cutaneous lesions– Sputum– Biopsy of affected organ

Click icon for audioBlastomycosis


• Direct detection methods– KOH prep– Histological stains– Look for large

spherical budding yeast with single bud connected to parent cell by a broad base


Mold - Blastomyces dermatitidis






Mold - Blastomyces dermatitidis




Yeast - Blastomyces dermatitidis

• Media– Cottonseed conversion agar– Incubate at 35ºC in ambient air for 1 week



Yeast - Blastomyces dermatitidis


Broad-Based Budding yeast


Other Test Methods


• Nucleic acid amplification assay


What is the diagnostic form for Blastomyces dermatitidis and what does it look like?

The yeast phase – it has a broad based single bud and is large in size.

Describe the appearance of the mold form of Blastomyces dermatitidis?

The mold form of Blastomyces is very nondescript. It has hyaline, septate hyphae. The conidiophores are short and unbranched and the conidia are hyaline, pyriform, unicellular, terminal, and solitary.

Coccidioidomycosis


• Coccidioides immitis

• Pathogenesis– 60% of infections are asymptomatic– Infection begins in lung– Can disseminate (1%)– Southwest U.S. desert area (endemic to

San Joaquin Valley)


• Specimen– Sputum– Biopsy of affected organ

Click icon for audioCoccidioidomycosis


• Direct detection methods– KOH prep, Calcofluor white stain– Histological stains– Look for spherule– No yeast form


Mold - Coccidioides immitis


• BIOHAZARD to lab personnel

• Media– BAP, Sab’s, Inhibitory Mold, and Mycosel

• Good growth at 3 days to 3 weeks

• Incubate– 25-30ºC– Ambient air– Up to 4 weeks







Spherule - Coccidioides immitis

• Not recommended

• Media– Special media incubated at 42ºC

• Can infect lab animals and do tissue biopsy (experimental)


Other Test Methods


• Nucleic acid amplification assay


What form for Coccidioides immitis is found in patient specimens?

The spherule. There is no yeast phase for this fungus.

What does Coccidioides immitis look like when cultured on SAB agar that has been incubated at 30°C?

Barrel-shaped alternating arthroconidia.

Paracoccidioidomycosis


• Paracoccidioides brasiliensis

• Pathogenesis– Infection begins in lung– Can be asymptomatic and then

disseminate to nasal and oral mucosa, gingivae, or conjunctivae

– South America (South American Blastomycosis)


• Specimen– Sputum– Biopsy of affected organ

Click icon for audioParacoccidioimycosis


• Direct detection methods– KOH prep, Calcofluor white stain, and

Histological stains– Look for large

round or oval, multiple budding yeast cells (“mariner’s wheel”)


Mold - Paracoccidioides brasiliensis









Mold - Paracoccidioides brasiliensis

• Media– Blood enriched media– Incubate at 35ºC in ambient air for 4 weeks




Yeast - Paracoccidioides brasiliensis

Other Test Methods



What is the diagnostic form for Paracoccidioides brasiliensis and what does it look like?

The yeast form appears as a large multiple budding yeast that looks like a mariner’s wheel.

In Summary …

• Diseases– All begin infection in lungs– Disseminate

• Identification– Demonstrate dimorphism– Direct specimen exam– Culture (mold and yeast forms)– Other testing

Systemic Dimorphic FungiClick icon for audio

Who am I?

Coccidioides immitis

Growth at 25ºC Sputum – silver stain

Who am I?

Blastomyces dermatitidis

Growth at 25ºC Growth at 35ºC

Who am I?

Histoplasma capsulatum

Growth at 25ºC Wright’s stain of blood

Date post:	21-Dec-2015
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Mycology Systemic Dimorphic Fungi Division of Medical Technology Carol Larson MSEd, MT(ASCP) Please...

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