Organisms Causing
Systemic Mycoses
Objectives – List two properties that the systemic dimorphics share.
Discuss conversion of the dimorphic yeasts
Identify from cases using colonial, morphological and geographic information, and diseases, the dimorphic fungi.
Differentiate the systemic dimorphic fungi from similar organisms previously discussed.
Describve the diseases, transmission, causative agents, of blastomycosis, paracocciodes, histoplamosis, and cocciomycosis.
Lab objectives
Describe any additional safety precautions needed when working with the systemic dimorphic fungi.
Using lactophenol cotton blue or tissue stains – identify Blastomyces dermatitidis, Paracocciodes barasilienses, Histoplasma capsulatum, and Cocciodes immitis.
Explain the method from converting these molds to yeast.
Describe exoantigen testing
Organisms
Histoplasma capsulatum
Blastomyces dermatitidis
Coccidioides immitis
Paracoccidioides brasiliensis
Pneumocytis carinii
Safety considerations
ALL handling of specimens and cultures MUST be performed in a biological safety cabinet
Do not open plates on benchtop
Plates should be sealed
If C. immitis is suspected, use tubed media instead of plates
Transmission and pathogenesis
Transmission is by inhalation of airborne conidia which are normally present in soil
Organisms are located in distinct geographical areas
Disease severity is dependent upon infective dose and patient’s immune status
Competent hosts: asymptomatic to mild respiratory disease
Compromised hosts: dissemination is common
Cultural characteristics
Very slow growing
Up to 6 weeks for growth (except C. immitis)
Must do direct examinations
Experimental: PCR testing of direct specimens
Colonial morphology varies with isolation media
Use both enriched (BHIA) and selective media
Classic morphology is described on SAB
Historically, definitive identification has been made by demonstrating both a yeast or tissue phase (at 370C) and a mold phase (at room temperature)
Methods of identification of
organism grown in culture
Exoantigen testing
DNA probe
Microscopic morphology
Conversion to yeast or tissue phase
Serological testing
Four-fold rise in antibody titer between acute and convalescent paired sera
Histoplasma capsulatum
Causes histoplasmosis (Darling’s or spelunker’s disease)
Distribution
Ohio and Mississippi River valleys, Appalachian mountains
Organism is spread by inhalation of airborne conidia
Organism multiplies in bird droppings and bat guano
Primary disease
90-95% are asymptomatic or sub-clinical, with a self-limiting mild respiratory infection
High percent of population in endemic areas are skin test positive for organism
Acute pulmonary disease
Night sweats, cough, fever and weight loss
Some develop pulmonary cavitary lesions resembling TB
Organism is able to multiply in macrophages (observed as pseudoencapsulated yeasts)
Dissemination is rare in the immuno-competent
Disseminated disease
Immune competent patients
Chronic disease of the adrenals, liver, kidneys, skin, oral mucosa, eye and CNS
Treatment: amphotericin B (>90% successful)
Immunocompromised patients
Rapidly fatal disease
Organism can be found throughout body, even in peripheral blood monocytes
Direct specimen examination
Specimens
Sputum, blood, bone marrow, lymph nodes, biopsy of infected tissue
Wright Giemsa stain of blood/bone marrow
Intracellular clusters of round to oval yeasts with narrow necked budding
Seen in macrophages and histiocytes
Culture characteristics
370C
Rough, mucoid cream to tan colonies
May need several transfers to convert from mold to yeast phase
Room temperature
Slow growing
Starts moist white to brown aerial mycelium glabrous, velvety or wooly colonies
Original isolates on BHIA should be transferred to SAB to observe characteristic morphologies
04Histoplasm
*
mold
Microscopic morphology at 370C
Small, single budding yeast
Occasional abortive hyphae may be seen
Microscopic morphology at
room temperature
Smooth-walled or tuberculate macro-conidia formed at 900 to hyphae
Round or tear drop microconidia may be seen
Macroconidia may be confused with contaminants:
Sepedonium sp.
Chrysosporium sp.
*
histo
*
Sepedonium
Identification
Exoantigen testing
Conversion of mold to yeast phase
DNA probes and other molecular techniques
Blastomyces dermatitidis
Causes North American blastomycosis or Gilchrist’s disease
Distribution
South of the Ohio and east of the Mississippi Rivers
Transmission is by inhalation of conidia or hyphal fragments
Organism proliferates near riverbanks surrounded by rotting wood
Disease
Men are more often affected than women
Associated with outdoor occupations/activities
Begins as a respiratory infection
40-50% remain asymptomatic
Progresses to chronic, suppurative and granulomatous infection
First disseminates to skin (ulcerated and crusted or weepy lesions) and bones (pain and loss of function)
Without therapy (amphotericin B or azoles), prognosis is poor
Direct specimen examination
Specimens
Sputum, skin biopsy, bone
Broad-based budding yeast with thick refractile walls
Organism does not survive well in clinical specimens
Culture immediately
Culture characteristics
370C
Waxy, wrinkled, cream to tan colonies
Room temperature
Initially: yeast-like colony
Develops into a white cottony colony that turns tan with
age
Conversion of mold to yeast phase takes 4-5 days
*
Mold phase
08BDermatit
Microscopic morphology at 370C
Thick walled, broad based budding yeast
Daughter cell separates from mother cell when both are the same size
Microscopic morphology at
room temperature
Single, smooth walled conidia at ends of short conid-iophores or directly on hyphae
“lollipops”
Resembles:
Scedosporium sp.
Chrysosporium sp.
Identification
Exoantigen testing
DNA probe
Mold to yeast phase conversion
Very difficult to perform
Coccidioides immitis
Causes coccidiomycosis (San Joachin Valley fever, desert fever)
Distribution
Southwestern deserts of US
Transmission
Inhalation of arthroconidia (organism is found in the soil)
Arthroconidia are resistant to heat, dryness and salinity
Disease
60% of infected patients remain asymptomatic
40% develop a mild to severe flu-like illness
Immune competent individuals fully recover life long immunity
? Reactivation of disease in the immunosuppressed
Good prognosis for primary disease; often fatal if disseminated
Treatment: amphotericin B or azoles
Disseminated disease
May be gradual or rapid
May form cavitary lung lesions
Seen in patients with underlying lung disease or diabetes
Spread via lymphatics to bone, skin, joints, lymph nodes, adrenals and CNS
Risk factors for chronic disease
Immunodeficiency
Pregnancy
Dark skin
Direct specimen examination
10-60 spherule is usually seen in pathology
Thick refractile wall
Loaded with endospores (2-4 each)
Cavitary lesions may also contain arthro-conidia
*
spherule
Culture characteristics
Grows at both room temperature and 370C in 4-5 days
Starts as a moist white colony
Later is covered by fluffy white mycellium
Grows on routine bacteriological media
No conversion to spherule phase in culture
Microscopic morphology at
room temperature
Septate hyphae
Thick-walled, barrel-shaped arthroconidia
Alternating empty disjunctor cells
Maybe confused with
Geotrichum sp.
Trichosporon sp.
Identification
Tissue spherules with releasing endospores
Exoantigen testing
Paracoccidioides brasiliensis
Endemic in South America (esp. Brazil)
Primary disease is often asymptomatic
50% of cases disseminate
Causes paracoccidiodomycosis
Organisms are inhaled pulmonary disease similar to TB
Trauma to oral mucosa
Ulcers of the mucous membranes, enlarged cervical lymph nodes
Death occurs within 2-3 years due to dissemination or malnourishment
Direct specimen examination
Specimens
Sputum, lymph node biopsies, mucosal biopsy
Multiple budding yeast
“ship’s wheel”
Culture characteristics
Room temperature
Slow growing
Starts smooth but later becomes covered with white to tan mycelium
370C
Waxy, wrinkled colonies
Cream to tan colored
Conversion to yeast phase requires 3-7 days
*
mold
*
yeast
Microscopic morphology
at room temperature
Branched septate hyphae
Intercalary and terminal chlamydo-spores
Microscopic morphology
at 370 C
Thick walled, multiple budding yeast
“mariner’s wheel”
“Mickey Mouse ears”
*
Direct smear
Homework
Read module 7 and answer review questions.
Do the final exam
Describe conversion of mold to yeast phase
Explain exo-antigen testing.
Make a table for the four systemic dimorphic fungi. Tell the specimen where they can be isolated from, geographically where they are found, what are the most identifying features.
What extra precautions should you take when working with systemic dimorphic fungi?
Identify the genus of this mold
Identify this mold and yeast phase from a landscaper clearing brush
Name this species of Actinomycetales group
What is this disease called it reminds you of cauliflower.
*
mold
*
histo
*
Sepedonium
*
Mold phase
*
spherule
*
mold
*
yeast
*
Direct smear
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