VIII. SYSTEMIC FUNGI

Most systemic fungi are ___, exhibiting a nonmold (e.g., yeast) parasitic phase at ____ and a mold (or mycelial) saprobic phase at _____

dimorphic ; 35–37°C ; 25–30°C.

This fungal group is often acquired via inhalation and can disseminate to any of the body’s organ systems.

Systemic Fungi

Identifying characteristics

• Identification is based on temperature and medium requirements and colony and microscopic morphology.

• Most are very slow growers and require 3–7 weeks to grow.

• Because the mold forms are highly infective, slants are used for culture.

Systemi Fungi 

Systemi Fungi 

• Colonies are membranous and develop _____.

• _____ identification is necessary in species identification.

• Conversion of dimorphic fungi from the mold to yeast phase is confirmation that the fungus in question is dimorphic.

• tan aerial mycelia

• Conidia

What are the systemic dimorphic fungi?

a. Blastomyces dermatitidis (blastomycosis)

b. Coccidioides immitis (cocccidioidomycosis)

c. Histoplasma capsulatum (histoplasmosis)

d. Paracoccidioides brasiliensis (paracoccidioidomycosis)

e. Talaromyces (Penicillium) marneffei (talaromycosis formerly penicilliosis)

B C H P T

• A respiratory infection that can affect the skin and bones.

• Infections are acquired by inhalation of conidia or hyphae and can be mild to chronic

Blastomycosis

• The precise environmental location of this fungus is unknown.

• Outbreaks have occurred following contact with moist environments such as streams and rivers and contact with decaying vegetation.

• More cases occur in males than in females.

Blastomyces dermatitidis

B. dermatitidis can be cultured from ___ or ___

tissue or body fluids.

Identifying characteristics

a. Microscopic appearance

• The mold phase is characterized by the presence of single smooth walled, round to oval conidia at the ends of short conidiophores.

• Can be confused with Scedosporium apiospermum or Chrysosporium spp.

b. Yeast phase: Large, round, thick-walled, budding yeasts with broad based blastoconidia

Blastomyces dermatitidis

B. dermatitidis can be confused with

Scedosporium apiospermum or Chrysosporium spp.

Identifying characteristics

Culture

• At room temperature, initially a yeastlike colony develops, and over time the colony will become fluffy white to tan.

• Conversion from the mold to yeast phase requires 4–6 days.

Blastomyces dermatitidis

Culture: Blastomyces dermatitidis

• At _____, initially a yeastlike colony develops, and over time the colony will become fluffy ____

• Conversion from the mold to yeast phase requires ___ days.

• room temperature ; white to tan

• 4–6

• An infection of the lungs, bones, joints, skin, lymph nodes, central nervous system, and adrenal glands.

• Infections can be acute or chronic and self-limiting or requiring medication

• Infections are often acquired through spore inhalation from the environment.

• Activities that increase airborne dust, such as plowing and construction, can facilitate transmission.

Coccidioidomycosis (valley fever)

Identifying characteristics

Microscopic appearance

• Branching thick-walled, rectangular (barrel-shaped) arthroconidia

• Tissue phase shows round, thick-walled spherule filled with small endospores.

• The tissue phase can only be grown under special conditions in vitro.

Coccidioides immitis (valley fever)

Identifying characteristics

Culture

• At 37°C on SABHI agar, colonies will appear moist and white and turn fluffy white in about a week.

• As with all mold phase fungi, always use a biological safety cabinet to prevent inhalation of spores.

Coccidioides immitis (valley fever)

• Can be a fatal pulmonary infection but can also affect the spleen, liver, kidneys, bone marrow, and heart.

• Infection is acquired by spore inhalation from barns, chicken houses, and bat caves.

• Has also been associated with guano, in particular from starlings and bats.

• Most infections occur in the southern and Midwestern United States and along the Appalachian Mountains.

• The major risk factor for infection is environmental exposure.

Histoplasmosis 

Identifying characteristics

Microscopic appearance

• The mold phase will show conidiophores at 90-degree angles to hyphae supporting smooth macroconidia (8–16 µm in diameter) with finlike edges (tuberculate).

• Microconidia are small (2–5 µm in diameter) and round to teardrop shaped.

• Yeasts appear as small single-budding cells that are unremarkable in morphology.

• In clinical specimens, yeasts are often found inside monocytes and macrophages.

Histoplasma capsulatum

• In clinical specimens, yeasts of Histoplasma capsulatum are often found inside _____

• monocytes and macrophages

Identifying characteristics

Culture

• On blood-containing media, the colonies are initially moist and develop tan aerial mycelia.

• Mature colonies are woolly and velvety and appear tan colored.

• Histoplasma capsulatum

•  A chronic granulomatous disease of the lungs and skin that can spread to the liver and spleen.

• Mostly found in South America

• Acquired by spore inhalation or ingestion

Paracoccidioidomycosis

Identifying characteristics

Microscopic appearance

• Yeast cells grown at 35–37°C are thick walled, with multiple budding yeast cells with very narrow necks.

• The mold phase exhibits mostly hyphae with intercalary and terminal chlamydoconidia.

Paracoccidioides brasiliensis

Identifying characteristics

Culture

• When grown on blood-containing media at 35–37°C, the colonies are waxy, wrinkled, and cream to tan colored.

• When grown on SDA or PDA at room temperature, colonies are initially smooth.

• Colonies become tan with aerial mycelia.

Paracoccidioides brasiliensis

• Typically spread by inhalation and affects the lungs.

• Infection can disseminate via the blood stream infecting other organs and producing a rash.

• Most cases occur in patients with acquired-immunodeficiency syndrome (AIDS) and other immunocompromised states.

• Located in southeast Asia, southern China, and eastern India

Talaromyces marneffei

Identifying characteristics

• The yeast cells are oval and small (3–8 µm) and resemble H. capsulatum.

• At 22–30°C, structures typical of the genus develop.

• Green aerial mycelium and reddish-brown hyphae are produced along with a red diffusible pigment.

Talaromyces marneffei

• Are nonfilamentous (do not produce hyphae) fungi found in the lower respiratory tract of humans and other animals

. Pneumocystis spp

Four species of Pneumocystis have been named; _____ is the name currently given to the species that infects humans.

Pneumocystis jirovecii

• P. jirovecii are found primarily in the____

lungs

P. jirovecii id diagnosed primarily with

nucleic acid probes and amplification assays

Microscopic examination

• Stains: Methanamine silver, periodic acid-Schiff, Giemsa, calcofluor white, etc.

• Microscopic appearance: Cysts (8 µm) contain several intracystic bodies, trophozoites (2–3 µm) with dark staining nuclei (depending on the stain).

Pneumocystis

Microscopic examination

• Microscopic appearance: Cysts (8 µm) contain several intracystic bodies, trophozoites (2–3 µm) with dark staining nuclei (depending on the stain).

Pneumocystis