Mycology 2020

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Mycology Update 2020
Margie Morgan, PhD, D(ABMM)
Mycormycetes Conidial Molds
Dematiacious Hyaline
Yeast
1

Starting point
Yeast are:
• Unicellular and bud to produce daughter cells
• Growth on solid media usually white to beige a...

Starting point
Molds:
• Produce hyphae and conidia [spores]
• Growth on solid media usually downy, fluffy, or cottony
• Mo...

Specimen Collection and Transport
• Fungi are very hardy organisms
• No special requirements for transport media
• Sterile...

Fungal Culture Media
• Sabouraud glucose agar (SABS)
All purpose Fungal media – antibiotic free
Contains 2% glucose, pH @7...

Fungal Culture Media
• Mycosel / Mycobiotic agar
• Selective SABs like agar containing chloramphenicol and cycloheximide
•...

• Inoculate specimen onto media and streak for isolation
• Seal plates with oxygen permeable tape to prevent environmental...

Yeast Identification
• Biochemical reactions have been used for decades to identify yeast. Recent
taxonomic updates and ne...

For years, Lactophenol Cotton Blue [LCB] adhesive tape preparation has
been used to assist with mold identification.
LCB m...

Safety in the Mycology Laboratory
• All identification work on molds must be performed in a BSL-2 biosafety
cabinet with H...

Gram stain
• Yeast cells stain positive (blue) using Gram stain procedure
• Examine Gram stain for budding cells to confir...

•KOH mount is used to detect yeast, pseudohyphae, and hyphae from
skin, hair, and nail specimens
•KOH dissolves the kerati...

• Yeast, pseudo-hyphae, and mycelial fungi bind with the Calcofluor
white stain reagent and fluoresce
• Read stain using a...

One drop of black ink is placed into one drop of
CSF on a microscope slide – examine using
light microscope (40X)
It is a ...

Grocott’s Methenamine Silver Stain [GMS] – yeast and
hyphae stain grey to black. Stains both living and dead yeast and
hyp...

Positive staining hyphae are magenta – will also stain structures
containing carbohydrate macromolecules (glycogen,
glycop...

Mucicarmine stains the polysaccharide capsule of Cryptococcus
neoformans and C. gatti pink. Will also stain mucin in fixed...

Helpful for the description of cellularity in tissue
and morphologic assessment of size, septations
and branching pattern ...

DIMORPHIC FUNGI
Important systemic pathogens with unique characteristics
19

What is a Dimorphic Fungus?
• Depending on temperature and conditions of environment, one fungi
demonstrates two forms:
• ...

Most Common Dimorphic Fungi
• Histoplasma capsulatum
• Blastomyces dermatitidis
• Coccidioides immitis and C. posadasii
• ...

Histoplasma capsulatum
• Epidemiology: World wide distribution,
in the USA endemic in Ohio, Missouri,
and Mississippi Rive...

Histoplasmosis
• 95% of infections are subclinical
• 5% infections are pulmonary with or without dissemination
• Who gets ...

Histoplasmosis Diagnosis
• Antigen detection in urine
• Quantitative enzyme immunoassay
• Performed on random collected ur...

H. capsulatum Culture
• Incubated at 30˚C – Growth of Mold
• Requires 2-8 weeks to grow
• Colony - white to brown and cott...

H.capsulatum Culture
• Incubated at 37*C – Growth of Yeast
• Requires 4-8 weeks to grow
• Colony – white to beige, creamy
...

H. capsulatum in
fixed tissue
• Infection begins by inhalation of
the microconidia
• Granulomas produced – can be
either c...

Histoplasma capsulatum – Yeast in fixed tissue
Usually intracellular within macrophages
Small yeast 2-4 um, minimal size v...

Leishmania amastigote
Note: kinetoplast (mitochondrial
DNA) next to nucleus
Toxoplasma tachyzoites
oval to crescent in sha...

Case History:
38 year old male
Newly diagnosed HIV disease/AIDS
CD4 count =3,
HIV Viral Load =220,000 copies
Anemia
Thromb...

The mold phase is identical to H. capsulatum.
Difference is the size of the yeast cell:
Note yeast cell of H. duboisii is ...

Blastomyces dermatitidis
• Epidemiology
• Ohio and Mississippi River valleys
• No association with animal or specific acti...

Blastomyces dermatitidis
• Culture at 30˚C - mold
• Grows in 2-3 weeks
• Fluffy white – buff colored mold, prickly
• Micro...

• Yeast phase grows at 35*C
• Slow growing taking up to 4 weeks
• Large yeast cell with considerable size variation, 8-20 ...

Blastomyces dermatitidis Histopathology
• Mixed pyogenic and granulomatous inflammation is observed in tissue
• Stains wel...

Coccidioides immitis and C. posadasii
• Taxonomy update: 2 species, Coccidioides posadasii
and C. immitis, close genetic r...

Coccidioidomycosis
• 60% of patients have asymptomatic infections
• 30% of patients have limited pulmonary disease
• The r...

Serologic diagnosis of Coccidioidomycosis
• Enzyme immunoassay (EIA): Sensitive and commonly used method
for diagnosing co...

Coccidioides Culture
• Culture at 30˚C grows the Mold phase
• Growth in 2-3 days, colony starts waxy and becomes wooly in ...

Coccidioides Look-a-likes
• Malbranchea species can look somewhat like C. immitis and
C. posadasii under the microscope us...

Coccidioides Histopathology
• No yeast cell produced in human tissue: Thick walled spherules variable in
size (10 – 80 uM)...

Case History:
75 year old male
Right Pleural Effusion
Lung nodule
Past medical history: Gout,
hypertension, anemia, obesit...

• Rhinosporidium seeberi (an aquatic parasite) forms spherules that
are larger than those of Coccidioides
• Rhinosporidium...

Paracoccidioides brasiliensis complex
• South American Blastomycosis – 80% of cases reported
from Brazil
• Most prevalent ...

Paracoccidioides
• Cultures at 30*C – mold, cultures usually not performed due to slow
growth and nonspecific sporulation
...

Tissue Exam of
Paracoccidioides brasiliensis complex
• Granulomatous inflammation with
giant cells formed in tissue
• Mari...

Sporothrix schenckii complex
• Sporotrichosis
• Cutaneous inoculation from penetrating
injury, such as cut or scrape with ...

Sporothrix schenckii complex
• 30˚C culture grows mold in 3 -5 days, starts
beige eventually turns brown/black
• Microscop...

Sporothrix schenckii Histology
• Pyogenic to granulomatous inflammation
• Yeast cells seldom observed in human tissue
• If...

• Disease: Cutaneous lesions most often, but Pneumonia or
systemic infection in HIV/AIDS
• Endemic in the tropics and SE A...

SUBCUTANEOUS FUNGAL
INFECTIONS
Mycetoma
Chromoblastomycoses
Phaeohyphomycosis
52

Mycetoma
• Subcutaneous fungal infections most commonly occur
in hot temperate parts of the world –
• Fungi grow in the so...

Actinomycotic Mycetoma
• 98% of cases
• Nocardia species most common agents of infection
• Sulfur granules are formed in t...

Edge of sulfur granule show thin filamentous bacteria: How can you tell if it is
Nocardia or Actinomyces? Best determinati...

Gram stain = filamentous Gram positive bacilli which can sometimes
stain poorly and appear speckled.
Modified Kinyoun Acid...

Nocardia spp can also cause primary Pulmonary
and Brain infection
Patients usually severely immune suppressed
Grows at 30 ...

Eumycotic Mycetoma
Infection with pigmented/black fungi (so called dematiaceous molds)
-Numerous black fungal species are ...

Thermoactinomycetes
• Gram positive filamentous rods related to Nocardia species
• Thermoactinomyces and Saccaropolyspora
...

Chromoblastomycosis
• Three characteristics:
• Wart like lesions (scarred and nodular) in subcutaneous tissue
• Muriform b...

Prototheca wickerhamii (Protothecosis)
• Algae without chlorophyll
• Causes skin lesions that can become nodular
• Most co...

Phaeohyphomycosis
Traumatic implantation of dark fungi into subcutaneous tissue
• Infections usually nodular lesions or cy...

What are the Black molds /
Dematiaceous molds
• Black colored colonies; both topside and the reverse
[underside of colony]...

Black Molds / Dematiacious molds
• Numerous species
• Difficult to identify requiring MALDI-TOF or 16S rRNA sequencing
• A...

Exophiala species
Most common Black Molds
Cladophialophora bantiana -
Associated with dissemination
infections that can ex...

Wangiella dermatitidis
Phialophora verrucosa
66

Alternaria species–
• Opportunistic fungal pathogen commonly found in nature
• Associated with sinusitis in normal host
• ...

Curvularia lunata
Center cell is the largest
• Opportunistic species/ disseminated infections are rare,
reported in patien...

Exserohilum rostrum
• Causative fungus in an outbreak due to a compound pharmaceutical [steroid]
product contaminated duri...

Scedosporium apiospermum complex/
(Pseudallescheria boydii complex)
• Cat fur-like gray colony / growth in 3 – 5 days at 3...

IMPORTANT YEAST CAUSING
HUMAN INFECTION
Candida species
Cryptococcus neoformans
Cryptococcus gattii
Trichosporon species
71

Candida species
• Candida species (@ 10 species infect humans)
• Yeast are usually found as normal flora in GI, GU and ski...

Most Important Candida species
• Candida albicans – @ 60% of Candida infections, usually susceptible to
fluconazole
• Cand...

Candida species
• Grow in 24 – 48 hours at 30-35*C
• Growth on many agars SABS, IMA, Blood agar… others
• Bacteria-like co...

Candida albicans
Identification
• Germ tube formation
• Incubate yeast in serum for 3-4 hrs at 35 ˚C
• Extension from yeas...

ChromAgar for the preliminary
identification of Candida species:
Four Candida spp turn a unique color
when grown on this a...

Candida Histopathology
• Pyogenic to granulomatous inflammation
• Most Candida species produce oval yeast cells (8 um) and...

Cryptococcus
neoformans
• In nature, a 2um non-encapsulated yeast cell
• Found in bird droppings (esp. pigeon)
C neoforman...

Cryptococcus gattii – closely related to C. neoformans
• Isolated from forested areas of the Pacific Northwest (British
Co...

Cryptococcus neoformans
and C. gattii
• Variable sized yeast cells (2 – 20 um)
• Virulence factor: Polysaccharide capsule
...

Grows on SABS and IMA in
1-3 days at 30 – 35*C
Mucoid colonies due to capsular
polysaccharide
Both C. neoformans & C. gatt...

Cryptococcus in tissue
82
Cryptococcus visible
clearing due to
capsule/ Yeast stain
poorly with
H&E stain
Mucicarmine stai...

Pneumocystis jiroveci (yeast like
fungus) could be confused with C.
neoformans – Careful! Central nuclear
staining in pneu...

Pneumocystis jiroveci
• Yeast like fungus
• Used to be named Pneumocystis carinii and considered a protozoan
parasite
• Ca...

Trichosporon
• T. asahii most common species
• Commonly inhabit the soil
• Colonize the skin/ gastrointestinal tract of hu...

CUTANEOUS AND SUPERFICIAL
MYCOSES
Malassezia furfur
Dermatophytes that cause Dermatophytoses
Microsporum species
Trichophy...

Malassezia furfur
• Most superficial of the dermatomycoses
• M. furfur can be normal flora on human skin
• More common on ...

Malassezia furfur
• Lipophilic yeast – oil required for growth
• Media for isolation must contain oil or use an oil overla...

Dermatophytes – Ringworm infections
• Hair, skin and nail infections
• 3 genera of fungi
• Microsporum species (many)
• Ep...

Positive KOH prep
Showing thin septate
fungal hyphae
Calcofluor white stain
with fluorescence –
thin fungal hyphae
90

Microsporum canis
• Ringworm infection acquired from infected dog or cat
• White colony grows in 5-7 days at 30* C/ yellow...

Microsporum gypseum –
• Mostly skin infection from exposure to contaminated soil
• Sandy colored colony that grows in 5-7 ...

Trichophyton rubrum
• Mostly infects skin and hair after
exposure to fomites, such as wet
towels or hair brushes
• Grows i...

Trichophyton
tonsurans
• White colony, grows in
5-7 days at 30* C
• Light yellow reverse
• No macroconidia
• only microcon...

Epidermophyton floccosum
• Infections in skin and
nails
• Khaki green colored
colony that grows in
5-7 days at 30*C
• Beav...

Opportunistic Hyaline Molds
Two groups:
(1) Narrow septate hyphae
(2) Broad non-septate hyphae
Infections in the immune su...

Hyaline/ narrow septate hyphae
• Hyaline – no color to the hyphae
• Regular septations in hyphae
• Grow on a variety of ag...

Aspergillus species
• Ubiquitous in nature @ 200 species
• Hyaline with regular septation
• Numerous round conidia produce...

Aspergillus Structure
99

Serology Tests Supportive not Conclusive for Diagnosis
Aspergillus Galactomannan Enzyme Immunoassay
• Detects circulating ...

Aspergillus fumigatus
• Ubiquitous airborne fungus, inhale conidia in nature
• One of most common species causing pulmonar...

Aspergillus flavus
• Normally found in cereals, grains, legumes
• Same disease potential as A. fumigatus/
pulmonary infect...

Aspergillus niger
• Black colony – visible black fruiting
heads grows in 2 – 5 days at 30*C
• Contaminate fruits and veget...

Aspergillus terreus • Infection primarily in the immune
compromised host
• Sandy colored colony grows in 3-5
days at 30*C
...

Aspergillus – fruiting head seldom seen in fixed tissue
usually dichotomous (continuous) branching septate hyphae which
br...

Fusarium species
• Common in nature/plants
• Fuchsia colored colony grows in 3-5 days 30*C
• Disease related to immune sta...

Scopulariopsis species
• Found in soil and grows on plant
• Infections: Nail, skin, sinusitis, pulmonary and may
dissemina...

Penicillium species –
• One of the most common molds in the environment
• Cause of bread mold
• Uncommon cause of human di...

MUCORMYCOSIS/
ZYGOMYCOSIS
Fungi in the Order Mucorales
• Hyaline
• Broad hyphae without septation
• Sporangium (sack) with...

Mucormycosis/Zygomycosis
• Found in soil, rotten fruit and vegetables
• Rhinocerebral mucormycosis - classic infection
• D...

Rhizopus species Absidia (Lichtheimia complex)
Mucor species
No rhizoids
Rhizoids
Order Mucorales
Distant rhizoid
111

90˚ angle branching can be seen, rare to no septations,
ribbon like hyphae
Invades vessels and
can cause infarcts
and thro...

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