Dimorphic Fungi Flashcards
What steps are taken for identifying lab cultures of dimorphic fungi
- Direct smear (Giemsa, GMS, H/E, Gram stain, etc.)
- Growth at 22°-225°C (most will grow in presence of Cycloheximide) for mold usually on SAB, PDA, PFA, etc.
- Growth at 37°C for yeasts (enriched BHI)
- Several transfers often necessary to convert
List the organisms characterized as dimorphic fungi
- Sporothrix schenckii
- Histoplasma capsulatum
- Blastomyces dermatitidis
- Paracoccidioides brasiliensis
- Coccidioides immitis
- Penicillim marneffei
Growth temperature for molds
22°-25°C (room temperature)
Growth temperature for fungi
37°C (body temperature)
Which dimorphic form is infectious?
Mold
Sporothrix schenckii
- Microscopic morphology of yeast form
Cigar shaped
Sporothrix schenckii
- Microscopic morphology of mold form
Septate hyphae w/ flowerettes or rosettes of conidia
Histoplasma capsulatum
- Microscopic morphology of yeast form (direct examination)
- Small yeast inside monocytes or macrophages, usually clumps
- Seen sputum, lung washing or biopsies of LN, liver, etc.
- Gives a hint of a halo but there is NO CAPSULE
Histoplasma capsulatum
- Microscopic morphology of yeast form
Small
- Cannot use to diagnose!!
Histoplasma capsulatum
- Microscopic morphology of mold form
Spiked macroconidia
Blastomyces dermatitidis
- Microscopic morphology of yeast form
- Large
- Thick cell wall
- Single bud w/ a BROAD BASE
Blastomyces dermatitidis
- Microscopic morphology of mold form
Microconidia on short conidiophores
- Cannot use to diagnose!!
Paracoccidioidomycosis
- Microscopic morphology of yeast form
Large “mother” cell w/ multiple buds (“daughters”) = Mariner’s wheel
Paracoccidioidomycosis
- Microscopic morphology of mold form
Smaller version of Blastomyces dermatitidis
- Cannot use to diagnose!
This structure of Coccidioides immitiis contains endospores and is seen in sputum or tissue biopsies
Spherules
Coccidioides immitis
- Microscopic morphology of mold form
Arthroconidia w/ ragged ends
Penicillium marneffei
- Microscopic morphology of yeast form
Oval w/ crosswall; may resemble Histoplasma
- Cannot use to diagnose!
Penicillium marneffei
- Colony morphology
- Green to reddish-green aerial hyphae
- RED DIFFUSIBLE PIGMENT
Sporothrix schenckii
- Endemic areas
United States
Histoplasma capsulatum
- Endemic areas
Mississippi River Valley (OH river, MS river, Indianapolis)
Blastomyces dermtitidis
- Endemic areas
States adjacent to Mississippi and OH rivers
Paracoccidioides ibrasiliensis
- Endemic areas
Brazil and South America
Coccidioides immitis
- Endemic areas
Desert in Southwest US (Ca, AZ, NM, southwest TX)
Penicillium marneffei
- Endemic areas
SE Asia
Non-culture methods used for diagnosing Histoplasma capsulatum
- Skin test
- Serum Abs
- Urine Ag test
Why is the skin test not used in endemic areas of Histoplasma capsulatum and Coccioiodes immitis
80-85% of people would test positive and show anti-Histoplasma/Coccidioides Abs in their serum
Which non-culture method is the best for diagnosing for Histoplasma capsulatum and Coccidioides immitis?
Urine Ag test (disseminated Histoplasma disease)
Sporothrix schenckii
- At risk patient populations
Garderners, farmers, florists, horticulturists
Histoplasma capsulatum
- At risk patient populations
“Healthy” people
Blastomyces dermatitidis
- At risk patient populations
?
Paracoccidioides brasiliensis
- At risk patient populations
Farmers who come into contact w/ acidic soil
Coccidioides immitis
- At risk patient populations
Migrant workers, farmers, military, archeologists
Penicillium marneffei
- At risk patient populations
Immunocompromised patients
Sporothrix schenckii
- Clinical presentation
- Primary: non-healing ulcers at inoculation site (hand, finger, arm, leg)
- Secondary: linear series of nodules and draining ulcers along lymphatics
Histoplasma capsulatum
- Clinical presentation
- Calcification in lungs, liver, spleen
- Immune suppressed (disseminated disease)
Blastomyces dermatitidis
- Clinical presentation
- Asymptomatic → chronic pulmonary disease
- Cutaneous ulcers or pustules may mimic cancer (aids in diagnosis)
Paracoccidioides brasilensis
- Clinical presentation
- Respiratory infection
- Ulcerative lesions of mouth, nose, and GI
Coccidioides immitis
- Clinical presentation
“Valley Fever”
- BIOTERRORISM ALERT!!!
Penicillium marneffei
- Clinical presentation
Systemic disease
Why is Coccidioides often NOT classified as a true dimorphic fungus?
There is no yeast phase at 37°C
