This document discusses four systemic dimorphic fungi - Histoplasma capsulatum, Blastomyces dermatitidis, Coccidioides immitis, and Paracoccidioides brasiliensis. It describes their geographic distribution, diseases caused, methods of transmission, clinical manifestations, diagnostic techniques including culture characteristics and microscopic morphology in both mold and yeast phases, and safety precautions for working with these organisms. Proper identification requires demonstrating both mold and yeast phases of growth as well as other tests such as exoantigen testing and molecular methods.

1. 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 objectivesDescribe 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

2. Organisms Histoplasma capsulatumBlastomyces
dermatitidisCoccidioides immitisParacoccidioides
brasiliensisPneumocytis carinii
Safety considerationsALL handling of specimens and cultures
MUST be performed in a biological safety cabinetDo not open
plates on benchtopPlates should be sealedIf C. immitis is
suspected, use tubed media instead of plates
Transmission and pathogenesisTransmission is by inhalation of
airborne conidia which are normally present in soilOrganisms
are located in distinct geographical areasDisease severity is
dependent upon infective dose and patient’s immune
statusCompetent hosts: asymptomatic to mild respiratory
diseaseCompromised hosts: dissemination is common
Cultural characteristicsVery slow growingUp to 6 weeks for
growth (except C. immitis)Must do direct
examinationsExperimental: PCR testing of direct
specimensColonial morphology varies with isolation mediaUse
both enriched (BHIA) and selective mediaClassic morphology is
described on SABHistorically, 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

3. organism grown in cultureExoantigen testingDNA
probeMicroscopic morphologyConversion to yeast or tissue
phaseSerological testingFour-fold rise in antibody titer between
acute and convalescent paired sera
Histoplasma capsulatumCauses histoplasmosis (Darling’s or
spelunker’s disease)DistributionOhio and Mississippi River
valleys, Appalachian mountainsOrganism is spread by
inhalation of airborne conidiaOrganism multiplies in bird
droppings and bat guano
Primary disease90-95% are asymptomatic or sub-clinical, with a
self-limiting mild respiratory infectionHigh percent of
population in endemic areas are skin test positive for
organismAcute pulmonary diseaseNight sweats, cough, fever
and weight lossSome develop pulmonary cavitary lesions
resembling TBOrganism is able to multiply in macrophages
(observed as pseudoencapsulated yeasts)Dissemination is rare in
the immuno-competent
Disseminated diseaseImmune competent patientsChronic disease
of the adrenals, liver, kidneys, skin, oral mucosa, eye and
CNSTreatment: amphotericin B (>90%
successful)Immunocompromised patientsRapidly fatal
diseaseOrganism can be found throughout body, even in
peripheral blood monocytes
Direct specimen examinationSpecimensSputum, blood, bone

4. marrow, lymph nodes, biopsy of infected tissueWright Giemsa
stain of blood/bone marrowIntracellular clusters of round to
oval yeasts with narrow necked buddingSeen in macrophages
and histiocytes
Culture characteristics370CRough, mucoid cream to tan
coloniesMay need several transfers to convert from mold to
yeast phase
colonies Original isolates on BHIA should be transferred to
SAB to observe characteristic morphologies
04Histoplasm
*
mold
Microscopic morphology at 370CSmall, single budding
yeastOccasional abortive hyphae may be seen

5. Microscopic morphology at
room temperatureSmooth-walled or tuberculate macro-conidia
formed at 900 to hyphaeRound or tear drop microconidia may
be seenMacroconidia may be confused with
contaminants:Sepedonium sp.Chrysosporium sp.
*
histo
*
Sepedonium
IdentificationExoantigen testingConversion of mold to yeast
phaseDNA probes and other molecular techniques

6. Blastomyces dermatitidisCauses North American blastomycosis
or Gilchrist’s diseaseDistributionSouth of the Ohio and east of
the Mississippi RiversTransmission is by inhalation of conidia
or hyphal fragmentsOrganism proliferates near riverbanks
surrounded by rotting wood
DiseaseMen are more often affected than womenAssociated with
outdoor occupations/activitiesBegins as a respiratory
infection40-50% remain asymptomaticProgresses to chronic,
suppurative and granulomatous infectionFirst 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 examinationSpecimensSputum, skin biopsy,
boneBroad-based budding yeast with thick refractile

7. wallsOrganism does not survive well in clinical
specimensCulture immediately
Culture characteristics370CWaxy, wrinkled, cream to tan
coloniesRoom temperatureInitially: yeast-like colonyDevelops
into a white cottony colony that turns tan with ageConversion of
mold to yeast phase takes 4-5 days
*
Mold phase
08BDermatit

8. Microscopic morphology at 370CThick walled, broad based
budding yeastDaughter cell separates from mother cell when
both are the same size
Microscopic morphology at
room temperatureSingle, smooth walled conidia at ends of short
conid-iophores or directly on
hyphae“lollipops”Resembles:Scedosporium sp.Chrysosporium
sp.
IdentificationExoantigen testingDNA probeMold to yeast phase
conversionVery difficult to perform
Coccidioides immitisCauses coccidiomycosis (San Joachin
Valley fever, desert fever)DistributionSouthwestern deserts of
USTransmissionInhalation of arthroconidia (organism is found
in the soil)Arthroconidia are resistant to heat, dryness and
salinity
Disease 60% of infected patients remain asymptomatic40%
develop a mild to severe flu-like illnessImmune competent
disease in the immunosuppressedGood prognosis for primary

9. disease; often fatal if disseminatedTreatment: amphotericin B
or azoles
Disseminated diseaseMay be gradual or rapidMay form cavitary
lung lesionsSeen in patients with underlying lung disease or
diabetesSpread via lymphatics to bone, skin, joints, lymph
nodes, adrenals and CNSRisk factors for chronic
diseaseImmunodeficiencyPregnancyDark skin
Direct specimen examination10-
pathologyThick refractile wallLoaded with endospores (2-
each)Cavitary lesions may also contain arthro-conidia
*
spherule
Culture characteristicsGrows at both room temperature and

10. 370C in 4-5 daysStarts as a moist white colonyLater is covered
by fluffy white mycelliumGrows on routine bacteriological
mediaNo conversion to spherule phase in culture
Microscopic morphology at
room temperatureSeptate hyphae Thick-walled, barrel-shaped
arthroconidiaAlternating empty disjunctor cellsMaybe confused
withGeotrichum sp.Trichosporon sp.
IdentificationTissue spherules with releasing
endosporesExoantigen testing
Paracoccidioides brasiliensisEndemic in South America (esp.
Brazil)Primary disease is often asymptomatic50% of cases
disseminateCauses paracoccidiodomycosisOrganisms are
mucosa Ulcers of the mucous membranes, enlarged cervical
lymph nodesDeath occurs within 2-3 years due to dissemination

11. or malnourishment
Direct specimen examinationSpecimensSputum, lymph node
biopsies, mucosal biopsyMultiple budding yeast “ship’s wheel”
Culture characteristicsRoom temperatureSlow growingStarts
smooth but later becomes covered with white to tan
mycelium370CWaxy, wrinkled coloniesCream to tan
coloredConversion to yeast phase requires 3-7 days
*
mold

12. *
yeast
Microscopic morphology
at room temperatureBranched septate hyphaeIntercalary and
terminal chlamydo-spores
Microscopic morphology
at 370 CThick walled, multiple budding yeast“mariner’s
wheel”“Mickey Mouse ears”
*
Direct smear

13. HomeworkRead module 7 and answer review questions.
Do the final exam
Describe conversion of mold to yeast phaseExplain 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.