This document provides an overview of mycology, focusing on yeasts, molds, specimen collection and transport, culture media, and key pathogenic fungi such as Histoplasma capsulatum. Yeasts are unicellular and produce budding daughter cells, while molds are filamentous with hyphae that produce spores. A variety of specimens can be used for fungal culture. Important media include Sabouraud's agar and mycosel/mycobiotic agars. Dimorphic fungi like H. capsulatum exist in both mold and yeast forms depending on temperature. H. capsulatum causes histoplasmosis and has a small oval yeast phase. Identification methods for fungi include culture, microscopy

1. Mycology
Just the basics – meant for
board review or brief study of
this fascinating area of
microbiology!
Mycology

2. Starting point
Yeast are:
 unicellular / produce budding daughter cells
 colony on solid media are usually white to
beige and appear much like bacterial
colonies
 some genera produce mucoid colonies

3. Starting point
Molds are:
 Filamentous with hyphae
 Produce conidia [spores]
 Colonies on solid agar are downy, fluffy,
cottony
 Most mold colonies are pigmented which aid
in identification
hyphae
spores

4. Appropriate Specimens and Transport
conditions for Fungal disease diagnosis
 Fungi are very hardy organisms
 Specimens do not require special transport media for culture
submission
 Sterile containers should be used to prevent bacterial
contamination and numerous sites are appropriate for culture
 Respiratory specimens – sputum, bronchial lavage, brushings,
nasal sinuses
 Tissue biopsies
 Cutaneous - Skin scrapings, material from lesions
 Ocular
 Sterile body fluids including CSF
 Blood, bone marrow

5. Fungal Culture Media
 Sabouraud’s glucose agar (SABS)

6. Common Fungal Media
 Mycosel/Mycobiotic agars
 Selective SABS with chloramphenicol and cycloheximide
 used for culture of dermatophytes – fungi that cause skin, hair and
nail infections
 Brain heart infusion agar
 Primary recovery of all fungal organisms
 Can make it more selective by adding chloramphenicol and
cycloheximide
 All fungal cultures must be incubated for 4 weeks at 30˚C
 Lower temperature than bacterial culture incubation [35˚C]
 If plates are used for fungal cultures the plates must be sealed with
air permeable tape for laboratory safety

7. What effect does Cycloheximide have
when added to media?
 Prevents rapidly growing molds from overgrowing
dimorphics and dermatophytes
 This is the good aspect of cycloheximide in media
 Beware: it is not all good, it can suppress important
fungi from growing. Inhibited fungi include:
 Trichosporon beigelii
 Candida tropicalis
 Cryptococcus neoformans
 Yeast phase of Blastomyces
 Yeast phase of Histoplasma

8. Inoculate fungal media
Seal plates with tape to prevent culture
contamination and escape of fungal spores
Incubate at 30˚C for 4 wk
If growth occurs - perform proper identification methods:
Yeast identification methods are very similar to
methods used to identify bacteria. There are manual
and automated biochemical reactions capable of
identifying most yeast species. There are newer
methods [Mass spectrometry – MALDI-TOF and 16
sRNA sequencing that can also be used in the more
sophisticated mycology laboratory.
Processing of Fungal Cultures - stepwise

9. Lactophenol cotton blue [LCB] adhesive tape preparations are
the standard method used for mold identification.
The LCB mounting medium consists of phenol
lactic acid, glycerol and aniline cotton blue dye.
Clear adhesive tape touches a mold colony, picking
up fungal hyphae and pressed into one drop of LCB
If LCB prep is not able to
identify a mold 16sRNA
sequencing can be used
to identify problematic
molds in reference
laboratories.
Mold Identification

10. Safety in the Mycology Laboratory
 If a culture is growing a mold, it cannot be
opened on the bench top
 All mold work must be performed in a BSL-2
biosafety cabinet with Hepa filtration
 Yeast identification can be
performed on the bench top

11. Direct Exams used to identify fungi
directly from patient specimens
 Gram stain – all specimen types can be Gram
stained. Can only reliably detect yeast by Gram stain.
 KOH preparation – Skin, Hair or Nails examined for
both yeast and/or hyphae
 Calcofluor white stain – all specimen types can be
stained and examined for yeast and/or hyphae
 India ink – Primarily used for CSF for the detection of
Cryptococcus neoformans and C. gattii

12. Yeast cells stain blue [Gram positive]. Examine for
budding cells to confirm that it is a yeast cell and not
an artifact. Examination on oil immersion lens.
You can also detect pseudohyphae on Gram stain.
Mold can be difficult to identify on a Gram stain.
pseudohyphae
mold
pseudohyphae
Gram Stain

13. Used to detect yeast and/or hyphae in skin, hair
and nail specimens using 40X light microscope.
KOH dissolves keratin found in cell material
and frees hyphae from the cell
KOH exams can be difficult to interpret!
KOH – potassium hydroxide prep

14. Yeast, pseudohyphae, and mycelial fungi will bind
with the Calcofluor white stain.
Prep is interpreted using a fluorescence microscope.
Sensitivity and specificity is improved over the KOH
preparation.
Calcofluor white stain

15. One drop of black ink is placed
into one drop of CSF and it is
examined using a 40X lens on
light microscope
It is a “negative” stain because
it stains the background not the
yeast
The clearing is the
polysaccharide capsule of
Cryptococcus neoformans or
C. gattii. Specificity is improved
if you look for budding yeast
cells.
India Ink

16. Methenamine Silver Stain [GMS] –
yeast and hyphae stain grey to black.
Examine the hyphae for presence of septations in the
hyphae, broad or more narrow width and angle of branching.
Examine the size and budding pattern of observed yeast.
We will observe on later slides these criteria can assist in
identification.
Examination of fungi in fixed tissue

17. PAS-positive staining red against a
green or blue background
Periodic Acid Schiff [PAS]

18. Stain-Cryptococcus neoformans polysaccharide capsule
stains pink
Mucicarmine [Mucin] stain

19. great for cellularity, it is
the beginning but GMS, or
PAS show features of the
fungi better.
Hematoxylin and Eosin Stain

20. The Dimorphic Fungi
Important pathogens with some
unique characteristics

21. What does Dimorphic mean?
 Two forms exist for one fungus species depending on
temperature and conditions of environment
 Mycelial form
free living form found in nature and at laboratory temperature <=30˚C
 Yeast or yeast like form
parasitic phase found in human tissue or in the lab >= 35˚
Histoplasma capsulatum – mold
from 30˚C culture
Histoplasma capsulatum – yeast
from tissue and <=30˚C culture

22. Dimorphic Fungi capable of causing
systemic infection
 Histoplasma capsulatum
 Blastomyces dermatitidis
 Coccidioides immitis
 Paracoccidioides brasiliensis
 Sporothrix schenckii

23. Histoplasma capsulatum
 World wide distribution / In USA in Ohio,
Missouri, and Mississippi River valleys
 Associate with Bat guano (Spelunker) and bird
droppings

24. Histoplasmosis Disease
 95% of infections are subclinical
 5% infections:
 Progressive pulmonary
 Chronic systemic infection with dissemination to the RES
system including bone marrow
 Acute fulminating systemic disease (fatal)
 Reactivation disease can occur in elderly and
immunosuppressed (AIDS is a good example)
 Bone marrow exam is useful in diagnosing disseminated
infections
 Mucocutaneous lesions are common
and a site of dissemination

25. The yeast of Histoplasma capsulatum prefer to
be intracellular and inhabit Macrophages.
Yeast are small 2 – 4 um, regular in size, and
oval to round. Yeast do not have a capsule,
this is just a staining artifact.

26. H & E PAS
Gram Wright’s
Histoplasma will stain with a variety of stains

27. Histoplasmosis rapid diagnosis
 Antigen detection in urine
 Quantitative Enzyme immunoassay
 Random urine specimen
 Most useful for disseminated infection and chronic
pulmonary disease
 Antigen is detectable in >=85% of these infections
 Good for immune suppressed patients that do not
produce a detectable antibody response

28. Histoplasma capsulatum
 Fungal Culture incubated at 30˚ C
 Very SLOW growing taking 2 – 8 weeks to form colonies
 Colony is white to brown and cottony
 Microscopic appearance – tuberculated macroconidia that
are large and round (8 – 16 µM) plus small microconidia (2 -
4µM) [see picture]
 Microconidia are the infectious particle growing in nature and
capable of penetrating deep into the lung
 DNA probe must be used to confirm identification so there is
definitive identification
 Sepedonium species looks somewhat like Histoplasma and
is considered a look a like fungus

29. Histoplasma capsulatum
culture at 30˚ C is white and
cottony.
Microscopic exam:
Tuberculate [projections]
macroconidia is the
structure used for ID.
Microconidia are the
infectious particle.
Appearance in culture at 30 degrees C

30. Appearance in culture at
35 degrees C
 Culture @ 35˚C is yeast
 Grows as small yeast, round to oval, always
consistent in size and shape (2 -4 uM) narrow
neck at the budding juncture

31. Histoplasma capsulatum in tissue
 Granulomas are usually produced and can be
either caseating or non caseating
 Infection usually begins in the Lung
 Infection disseminates to organs of the
Reticuloendothelial System (RES) – with high %
of dissemination to the Bone Marrow
 Intracellular budding yeast (2 – 4 µM) are seen in
all tissues

32. Leishmania species
Note small round
kinetoplast next to nucleus
Toxoplasma
Histoplasma capsulatum
Beware of look alike organisms
in tissue specimens!!

33. H capsulatum var duboisii yeast cells are
8 – 10 uM in size, which is 2X the size of
regular Histoplasma capsulatum yeast cells.
H. capsulatum var duboisii disease
is found in Central Africa
Causes infection in skin and bone
The 30˚C culture is identical to
H capsulatum.
Unusual variant of H. capsulatum

34. Blastomyces dermatitidis
 Epidemiology
 Ohio and Mississippi River valleys
 No association with specific animal or activity
 Forrest and river banks?
 Primarily a pulmonary infection which may
disseminate to the skin and bone
Well demarcated skin lesion is typical
Scraping of skin lesions are full of
yeast cells

35. Blastomyces dermatitidis
 Culture at 30˚C
 Grows in 2- 3 weeks
 Fluffy white – buff colored mold, prickly
 Pear shaped conidia at the end of supporting
hyphae – looks like lollipops
 Look alike fungus – Chrysosporium species
 Do DNA probe test to confirm identification
Blastomyces
Chrysosporium

36. Slow growing yeast colony taking @ 4
weeks to form a colony
Yeast cell is 8 – 20 um in size and is
unique for it’s Broad Based Budding
pattern and the double contoured wall.
Blastomyces culture at 37 degrees C

37. Blastomyces dermatitidis histopathology
Mixed pyogenic and granulomatous
inflammation is observed in tissue with
Broad based budding yeast cells

38. Coccidioides immitis
 Endemic in SW USA, Mexico,
South America, in areas known
as the Sonoran life zone with a warm climate
and desert sands
Infection is from inhalation of fungal particles
found in the sand
 Coccidioides posadasii is a genetically related
to C. immitis. The two species are located in
different endemic regions, but produce the
same disease process

39. Coccidioidomycosis
 95% of infections are asymptomatic or with limited
symptoms
 The remaining 5% are focal pulmonary, progressive
pulmonary or disseminated infections. Dissemination
to the central nervous system is difficult to cure and
has a high fatality rate.
 Higher incidence of dissemination occurs in patients
with:
 defects in cell mediated immunity (HIV),
 darker skinned ethnic groups,
 pregnancy

40. Coccidioides immitis [posadasii]
 Culture at 30˚C
 Requires only 2 – 3 days to grow, colony starts waxy and
becomes wooly in around 7 – 10 days
 Under the microscope one looks for foci of septated hyphae with
thick walled barrel shaped arthroconidia with clear spaces in
between. The clear spaces are dead arthroconidia.
 Arthroconidia infectious particle in nature
 Very infectious to laboratory personnel

41. Coccidioides
 Malbranchea species can look like C. immitis under the
microscope
 Because of look-a-like fungi one needs to confirm
identification of Coccidioides immitis with DNA probe or
similar method to be sure!
Coccidioides Malbranchea

42. Barrel shaped alternating arthroconidia are
produced in cultures grown at both 30 and 35 C.
There is no yeast phase for C. immitis [posadasii]
No yeast phase with Coccidioides!

43. Coccidioides Histopathology
 Thick walled spherules (10 – 80 uM) with endospores
are seen in tissue. This is the second form of Cocci.
No yeast cells are produced in tissue for this fungus.
 Spherules are at all stages of development-
fragmented spherules to well formed with endospores
 Granulomatous inflammation with caseation is usually
observed

44. Development of Cocci spherules from the
inhalation of Arthroconidia from nature

45. Rhinosporidium seeberi forms spherules but much larger
than the Cocci spherules - they are usually > 80 uM in size.
Also R. seeberi almost always cause oral or nasal mass
lesions, unlike Cocci.
Oral or nasal mass lesions
of Rhinosporidium seeberi
Coccidioides
spherules
Cocci is not the only spherule forming
organism!

46. Paracoccidioides brasiliensis
 South American Blastomycosis –
endemic area Brazil, Venezuela, Columbia
 Inhale infectious particle from soil
 >95% of infections in males, possibly due to
estrogen inhibition of mycelial to yeast
transformation
 Disease presentation:
1. Pneumonia
2. Disseminated infection
3. Extrapulmonary lesions on the face and oral
mucosa

47. Paracoccidioides
 Cultures are usually not used in diagnosis
due to slow growth and nonspecific
sporulation
 Culture @ 37˚C
 Slow growing yeast
 Large yeast (10 – 30uM) with multiple daughter
buds (2 – 10 uM) in size
 Unique yeast cell known as the Mariner’s wheel or
Pilot’s wheel yeast

48. Mariner’s wheel yeast of
Paracoccidioides brasiliensis
If more than 2 buds off mother cell –
High likelihood it is Paracoccidioides

49. Sporotrichosis
 Sporothrix schenckii
 Cutaneous inoculation of fungus from penetrating
injury with a spore or thorn (rose bush)
 Initial skin lesion w/wo ulceration
 Lymph-cutaneous spread – bone – systemic
 Pulmonary and CNS infections are rare but
reported

50. Starts as one ulcerative lesion and then chains
Up the lymphatics – can involve lymph nodes
and bone

51. Sporothrix schenckii
 Dimorphic fungus
 MOLD PHASE
 30*˚C growth in 3 -5 days
 Turns brown to black over time
 Septate hyphae with conidia in daisy wheel
pattern
 YEAST PHASE
 At 37˚C small oval yeast cells,
elongated 2 – 5 µM, described as cigar bodies

52. Sporothrix schenckii
 Histology –
 Pyogenic – to – granulomatous inflammation
 Hard to find yeast in human tissue
 Asteroid body known as Splendore-Hoeppli
phenomenon can be seen – also seen in:
Zygomycetes (mucorales)
Aspergillus
Blastomycosis
Candida

53. Daisy like spore arrangement
Sporothrix
schenckii

54. Green colony with red diffusable pigment
Uncommon dimorphic fungus
The only species of Penicillium that is dimorphic
Causes skin lesions in tropics and
Pneumonia in immune suppressed
Penicillium marneffei

55. Penicillium marneffei yeast like cells in tissue

56. Subcutaneous Fungal
Infections
Very unique structures in tissue!

57. Subcutaneous Fungal Infections
Most common will be described
 Mycetoma [2 types]
 Actinomycotic – caused by higher bacteria
 Eumycotic – caused by dark pigmented molds
 Chromomycosis [Chromoblastomycosis]
 Phaeohyphomycosis
 Sporotrichosis

58. Mycetoma
 First observed in India and known
as Madura Foot or Maduromycosis
 Found in the hot temperate parts of
the world
 Three criteria describe Mycetoma:
1. Lesions lead to swollen extremities
2. Draining sinuses
3. Sulfur granules observed in tissue and found in the
weeping drainage
 Fungus grows on organic debris in soil
 Implanted into subcutaneous tissue from trauma

59. Swollen extremity and draining sinus with
sulfur granules
Sulfur Granule
Mycetoma

60. Mycetoma
 There are two types of Mycetoma:
1. Actinomycotic mycetoma – caused by higher bacteria
species
2. Eumycotic mycetoma – caused by the black molds
 Actinomycotic Mycetoma
 98% of cases of Mycetoma
 Nocardia species most common cause
 Sulfur granules formed in tissue and the granules vary in
color and contain a matrix of the filamentous bacteria

61. Gram stain as filamentous Gram positive bacilli – can be
poorly staining and appear speckled.
Nocardia are positive [red] on the Modified Kinyoun stain.
Modified acid-fast stain
[modified Kinyoun stain]
Gram stain of sputum
containing Nocardia
Nocardia

62. Edge of granule has thin filamentous bacteria
for both bacteria – Nocardia is modified acid fast
[PAF] positive and is aerobic bacteria. Actinomyces
is PAF negative and grows anaerobically.
Beware! Sulfur granule
caused by Actinomyces
israelii looks identical.
Actinomycotic sulfur granule - Nocardia

63. Requires 3 – 5 days to
grow on agar media [Sabs,
5% Sheep’s blood agar
Colony is dry and crumbly
Musty smell
Total of 85 species
Nocardia asteroides is the
most common species
isolated from human
infection
Identification by HPLC
or molecular methods
Nocardia species cause mycetoma, and
can also cause Pulmonary and Brain infections

64. Eumycotic mycetoma – subcutaneous
infection caused by the black molds
Numerous species of pigmented/black fungi found
naturally in the soil can cause this type of infection
Cause @ 2% of cases of mycetoma
Traumatic implantation injects the mold into the
subcutaneous tissue
Most common species of black mold include:
Cladophialophora (Cladosporium) carrionii
Cladophialophora bantiana
Phialophora verrucosa
Fonsecaea pedrosoi
Exophiala species
Wangiella species

65. Eumycotic sulfur granule – the granule is
full of a matrix of thick fungal hyphae

66. Chromomycosis/Chromoblastomycosis
 Three characteristics describe Chromomycosis
 Wart like lesions in subcutaneous tissue
 Sclerotic bodies observed in tissue
 Growth of dark/pigmented fungi
 Black mold naturally found in the soil cause
infection through abrasion/ implantation
 Black molds that can cause Chromomycosis:
 Cladophialophora [Cladosporium] carrionii
 C. bantiana
 Phialophora verrucosa
 Fonsecaea pedrosoi
 Exophiala species
 Wangiella species

67. Chromomycosis/Chromoblastomycosis
Wart like/Verrucous lesions
In subcutaneous tissue
Sclerotic Body/Medlar Body/
Copper Penny is the unique
structure found in tissue

68. Prototheca wickerhamii – the cause of
Protothecosis
 Algae without chlorophyll
 Causes skin lesions & nodules
 Most common in patients with suppressed immune
system
 Compare morula of Protothecosis to sclerotic body of
Chromomycoses

69. Phaeohyphomycosis
This infection is caused by traumatic
implantation of dark fungi into subcutaneous
tissue
 Variety of infections but nodules/lesions most
common with/without dissemination
 Dark hyphae only observed in tissue

70. Black molds/Dark molds
also known as Dematiaceous
fungi
Black colored colonies and the
reverse [back of colony] is also
black
Naturally brown hyphae and
spores
One of the major causes of mold
growth due to water damage!

71. Black Molds – Dematiaceous fungi
 Black colonies
 Brown hyphae and spores
 Numerous species
 Difficult to identify
 All have one of four types of sporulation
 Rhinocladiella-like
 Cladosporium-like
 Phialophora-like
 Acrotheca-like

72. Rhinocladiella type
sporulation

73. Phialophora type sporulation

74. Cladophialophora
[Cladosporium type sporulation]

75. Acrotheca type sporulation

76. Exophiala species
Black Molds that can cause
Mycetoma/Chromomycosis/Phaeohyphomycosis
These are difficult to identify but viewing is
necessary!
Cladophialophora bantiana

77. Wangiella dermatitidis
Phialophora verrucosa

78. Alternaria
Other black molds of importance:

79. Bipolaris
australiensis
Very invasive
fungal infection:
Skin, nasal
sinuses, bone
brain

80. Curvularia lunata
Center cell is the
largest

81. Exserohilum rostrum
 Associated with compounded pharmaceutical
[steroid] products contaminated with dust/dirt
 Used for infections into lumbar spine and
knee joints for pain management
 Meningitis
 Spinal abscess
 Synovial infections

82. Scedosporium apiospermum/
Pseudallescheria boydii
Cat fur-like colony

83. Important Yeast causing human
infection
Candida species
Cryptococcus neoformans &
Cryptococcus gattii

84. Cutaneous and Superficial Mycoses
 Candida species (@ 10 found in humans)
 Opportunistic pathogen involving skin or mucous
membranes from excessive exposure to moisture,
antibiotics, or immune suppression
 Yeast is from endogenous source – found as
normal flora in the GI and GU tracts and skin
 Variety of infections including: Thrush, vaginitis,
skin lesions, nail, diaper rash, to more serious
infections like fungemia and endoarditis.

85. Candida species
 Candida albicans – most common species
causing @ 60% of human yeast infections
 Candida glabrata, C. krusei, and C. tropicalis
are becoming more common in infection
 These 3 species are more likely
to be resistant to Fluconazole
 Candida parapsilosis has emerged
as a pathogen of children and IV lines

86. Candida species
 Grow in 24 – 48 hours
 SABS, IMA, BAP
 Bacteria-like colony – pasty white
 Budding yeast – oval @ 7-8 um in size
form pseudohyphae (look like sausage links)
 Exception **Candida glabrata is @ 4 µM in
size and does NOT form any pseudohyphae

87. Candida albicans
Identification
 Germ tube formation
 Incubate small amount of yeast in serum for 3-4hr at 35 ˚C
 Do not incubate >4 hr – this can lead to a false positive
reaction with C. tropicalis
 C. dubliniensis also positive (uncommon yeast isolate)
 Chlamydospore formation
 Growth on cornmeal agar >48 hrs
 Rudimentary structures
C. albicans
chlamydospore
C. glabrata only forms yeast
No pseudohyphae

88. ChromAgar for the
identification of Candida
Chromogenic substrates
Turn different colors with
4 different yeast species
Yeast with pseudohyphae

89. Candida Histopathology
 Pyogenic to granulomatous
 Usually observe yeast cells, pseudohyphae
and/or hyphae appearing structures
 Candida glabrata = smaller yeast cells and no
pseudohyphae
GMS stain of Candida glabrataCandida species not glabrata

90. Cryptococcus
neoformans
 In nature forms a 2um non-encapsulated
yeast cell. It is associated with bird
droppings (esp. pigeon). C neoformans is
enriched by the nitrogen in the droppings.
 Yeast cells are inhaled – travels through the
pulmonary system with hematogenous
spread to brain and meninges
 Has tropism to the meninges
 Infects mostly compromised hosts - AIDS

91. Cryptococcus neoformans
 Irregular sized (2 – 20uM) yeast cells
 Polysaccharide capsule is virulence factor and it’s presence is used in
diagnostic tests for C. neoformans
 India ink exam of CSF is a negative staining method/capsule
not stained,
 Sensitive test for AIDS
patients (90% sensitive)
 Cryptococcal antigen test – capsular polysaccharide is
detected in both CSF and serum,
 Test for diagnosis and can
also follow recovery with
falling titer /more sensitive
than India ink
 Grows on mycologic agars but is sensitive to cycloheximide –
 Mucoid colonies due to capsule po;ysaccharide formation
 Urease enzyme + Inositol assimilation +
 Brown colonies produced on bird seed agar

92. Cryptococcus gattii – a closely related
relative of C. neoformans
 Isolated from forested area of the Pacific Northwest
(British Columbia, Washington, and Oregon)
 Infection of normal and immune suppressed hosts
 Mostly Pulmonary disease [Cryptococcoma] but can
develop meningitis
 Culture and staining identical to C. neoformans except
for L Canavanine glycine bromthymol blue medium –
C

93. Positive India Ink
Urea medium demonstrating urease
enzyme activity of Cryptococcus
Observe
Budding cells
Variability in size
Positive
Mucoid colonies of
C. neoformans and
C. gattii

94. C. neoformans/C. gattii forms
brown colonies on Birdseed agar

95. Mucicarmine stain
Stains the capsular polysaccharide of capsule
Pneumocystis jeroveci could
be confused with C.
neoformans – Careful!
Central nuclear staining
C. neoformans/ C. gattii

96. Cutaneous and Superficial Mycoses
Malassezia furfur
Dermatophytes

97. Malassezia furfur
 Pityriasis versicolor
 Most superficial of the dermatomycoses
 Found as normal flora on the skin,
 More common on oily skin or high use of skin oils
 Diseases:
 Skin: macules, papules, patches, plaques on chest
back and shoulders with either hypo or hyper
pigmentation – does not invade into deeper tissues
 Fungemia in neonates caused by skin flora
tunneling in the IV lipid feeding lines

98. Malassezia furfur
 Lipophilic yeast – oil required for growth
 Media used for culture must contain oil or have oil
overlay
 Small budding yeast 2 – 4 µM with collarette
Spaghetti and meatballs

99. Size range for Yeast
 Candida glabrata/Histoplasma capsulatum
 2 – 4 um
 Candida species
 8 – 10 um plus pseudohyphae
 Cryptococcus neoformans/gattii
 2 – 20 um
 Blastomyces dermatitidis
 8-15 um

100. Dermatophytes – Ringworm infections
 Hair, skin and nail infections
 3 genera of fungi
 Microsporum species (many)
 Epidermophyton floccosum
 Trichophyton species (many)
 Disease described by area of the body infected:
tinea capitis (head), t. pedis (foot)
 Usually a clinical diagnosis not requiring culture
 Can do a KOH prep or Calcofluor white prep to
visualize fungal hyphae

101. Positive KOH prep
Showing thin septate
fungal hyphae
Calcofluor white stain
with fluorescence –
thin fungal hyphae

102. Microsporum canis
Main cause of ringworm from dog and cat
White colony/ yellow on backside of colony
Tuberculate macroconidia [spiny projections]
Few if any microconidia

103. Microsporum gypseum infection from
exposure to contaminated soil

104. Trichophyton
Rubrum
White colony with
red diffusable
pigment
Pencil shaped
Macroconidia
Many micro-
Conidia
Infection from
fomites
Red diffusible pigment

105. Trichophyton
tonsurans
Ballooning
Microconidia
Primary cause of
epidemic
ringworm in
children

106. Epidermophyton floccosum
Beaver tail large spores without microconidia
Khaki green colony

107. Opportunistic Fungal Pathogens
Infections in the immune suppressed
host or special circumstances
Hyaline molds
Black molds

108. Opportunistic Fungi - hyaline
 Hyaline – no color to the hyphae
 Regular septations in the hyphae
 Branching – angle can be helpful in
identification
 Usually grow in 3 – 5 days at 30˚C
 ??? of species thousands– taxonomy
changing daily

109. Aspergillus species
 Hyaline with septations
 Numerous round conidia
 In tissue - Branching at 45 degree angle
 Primarily pulmonary infection in immune suppressed
 Invade vessels, cause thrombosis & infarctions

110. Aspergillus Structure

111. Aspergillus species
Four species most common in human infections:
1. Aspergillus fumigatus
2. Aspergillus flavus
3. Aspergillus niger
4. Aspergillus tereus – unique and important – only
Aspergillus species resistant to Amphotericin B
Aspergillus Galactomannan Enzyme immunoassay –
detects circulating Aspergillus antigen in the blood
and/or bronchial lavage fluid
Problems with low sensitivity and specificity
False positive reaction in patients on therapy with
Piperacillin/Tazobactam

112. Aspergillus fumigatus
Blue/Green colony
Phialids with spores are
Directed upward

113. Aspergillus flavus
Green colony
Orange colored spores
that surround the vesecle

114. Aspergillus niger
Black colony
Black spores surround the vesicle

115. Aspergillus terreus
Sandy colored colony
Aleurioconidia
Resistance to Amphotericin B

116. Aspergillus – fruiting head and dichotomous
branching septate hyphae with branching at 45* angle
Can appear much like that
of Pseudallescheria boydii!
P. boydii hyphae is a bit
thinner. The appearance in
culture can differentiate the
two fungi.

117. Fusarium species –
Common in nature/plants
disease related to immune
status of host
Infections reported:
Disseminated in bone marrow
transplants
Corneal infections in contact
lens wearers

118. Scopulariopsis species –found in soil and
plants
Infections: Nail, skin, sinusitis, pulmonary and
disseminated

119. Paecilomyces species
Isolated from soil and food
Opportunistic pathogen in the
immune suppressed

120. Penicillium species – most common mold
in the environment, bread mold, uncommon
cause of human disease

121. Mucormycosis/Zygomycosis
Hyaline
Broad non-septate hyphae

122. Mucormycosis/Zygomycosis
 Infections in diabetics, the elevated
glucose enriches fungal growth – classic
infection is rhinocerebral mucormycosis
 Sinus and pulmonary infection in the immune
suppressed host
 Broad, hyaline, aseptate hyphae produced
 Cultures grow in 24 hrs, coarse aerial hyphae
 Can be difficult to culture – tube like hyphae killed
during manipulation and plating
 Should not grind tissue
 Mince tissue and place on agar

123. Zygomycete – coarse, aerial hyphae after 24
hours on SABS agar at 30˚C

124. Rhizopus Absidia
Distant rhizoids
Mucor
No rhizoids
Rhizoids

125. 90˚ angle branching, aseptate, ribbon like
Invades vessels and can cause
infarcts and thrombi
Zygomycetes (Mucorales)