Dimorphic Fungi

Question 1

What steps are taken for identifying lab cultures of dimorphic fungi

Answer 1

• 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

Question 2

List the organisms characterized as dimorphic fungi

Answer 2

• Sporothrix schenckii
• Histoplasma capsulatum
• Blastomyces dermatitidis
• Paracoccidioides brasiliensis
• Coccidioides immitis
• Penicillim marneffei

Question 3

Growth temperature for molds

Answer 3

22°-25°C (room temperature)

Question 4

Growth temperature for fungi

Answer 4

37°C (body temperature)

Question 5

Which dimorphic form is infectious?

Answer 5

Mold

Question 6

Sporothrix schenckii

- Microscopic morphology of yeast form

Answer 6

Cigar shaped

Question 7

Sporothrix schenckii

- Microscopic morphology of mold form

Answer 7

Septate hyphae w/ flowerettes or rosettes of conidia

Question 8

Histoplasma capsulatum

- Microscopic morphology of yeast form (direct examination)

Answer 8

• 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

Question 9

Histoplasma capsulatum

- Microscopic morphology of yeast form

Answer 9

Small

- Cannot use to diagnose!!

Question 10

Histoplasma capsulatum

- Microscopic morphology of mold form

Answer 10

Spiked macroconidia

Question 11

Blastomyces dermatitidis

- Microscopic morphology of yeast form

Answer 11

• Large
• Thick cell wall
• Single bud w/ a BROAD BASE

Question 12

Blastomyces dermatitidis

- Microscopic morphology of mold form

Answer 12

Microconidia on short conidiophores

- Cannot use to diagnose!!

Question 13

Paracoccidioidomycosis

- Microscopic morphology of yeast form

Answer 13

Large “mother” cell w/ multiple buds (“daughters”) = Mariner’s wheel

Question 14

Paracoccidioidomycosis

- Microscopic morphology of mold form

Answer 14

Smaller version of Blastomyces dermatitidis

- Cannot use to diagnose!

Question 15

This structure of Coccidioides immitiis contains endospores and is seen in sputum or tissue biopsies

Answer 15

Spherules

Question 16

Coccidioides immitis

- Microscopic morphology of mold form

Answer 16

Arthroconidia w/ ragged ends

Question 17

Penicillium marneffei

- Microscopic morphology of yeast form

Answer 17

Oval w/ crosswall; may resemble Histoplasma

- Cannot use to diagnose!

Question 18

Penicillium marneffei

- Colony morphology

Answer 18

• Green to reddish-green aerial hyphae

- RED DIFFUSIBLE PIGMENT

Question 19

Sporothrix schenckii

- Endemic areas

Answer 19

United States

Question 20

Histoplasma capsulatum

- Endemic areas

Answer 20

Mississippi River Valley (OH river, MS river, Indianapolis)

Question 21

Blastomyces dermtitidis

- Endemic areas

Answer 21

States adjacent to Mississippi and OH rivers

Question 22

Paracoccidioides ibrasiliensis

- Endemic areas

Answer 22

Brazil and South America

Question 23

Coccidioides immitis

- Endemic areas

Answer 23

Desert in Southwest US (Ca, AZ, NM, southwest TX)

Question 24

Penicillium marneffei

- Endemic areas

Answer 24

SE Asia

Question 25

Non-culture methods used for diagnosing Histoplasma capsulatum

Answer 25

• Skin test
• Serum Abs
• Urine Ag test

Question 26

Why is the skin test not used in endemic areas of Histoplasma capsulatum and Coccioiodes immitis

Answer 26

80-85% of people would test positive and show anti-Histoplasma/Coccidioides Abs in their serum

Question 27

Which non-culture method is the best for diagnosing for Histoplasma capsulatum and Coccidioides immitis?

Answer 27

Urine Ag test (disseminated Histoplasma disease)

Question 28

Sporothrix schenckii

- At risk patient populations

Answer 28

Garderners, farmers, florists, horticulturists

Question 29

Histoplasma capsulatum

- At risk patient populations

Answer 29

“Healthy” people

Question 30

Blastomyces dermatitidis

- At risk patient populations

Answer 30

?

Question 31

Paracoccidioides brasiliensis

- At risk patient populations

Answer 31

Farmers who come into contact w/ acidic soil

Question 32

Coccidioides immitis

- At risk patient populations

Answer 32

Migrant workers, farmers, military, archeologists

Question 33

Penicillium marneffei

- At risk patient populations

Answer 33

Immunocompromised patients

Question 34

Sporothrix schenckii

- Clinical presentation

Answer 34

• Primary: non-healing ulcers at inoculation site (hand, finger, arm, leg)
• Secondary: linear series of nodules and draining ulcers along lymphatics

Question 35

Histoplasma capsulatum

- Clinical presentation

Answer 35

• Calcification in lungs, liver, spleen

- Immune suppressed (disseminated disease)

Question 36

Blastomyces dermatitidis

- Clinical presentation

Answer 36

• Asymptomatic → chronic pulmonary disease

- Cutaneous ulcers or pustules may mimic cancer (aids in diagnosis)

Question 37

Paracoccidioides brasilensis

- Clinical presentation

Answer 37

• Respiratory infection

- Ulcerative lesions of mouth, nose, and GI

Question 38

Coccidioides immitis

- Clinical presentation

Answer 38

“Valley Fever”

- BIOTERRORISM ALERT!!!

Question 39

Penicillium marneffei

- Clinical presentation

Answer 39

Systemic disease

Question 40

Why is Coccidioides often NOT classified as a true dimorphic fungus?

Answer 40

There is no yeast phase at 37°C