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Copyright 2011 by MediaLab, Inc. All rights reserved.

Mycology: Hyaline and Dematiaceous Fungi

Elmer W. Koneman, MD

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Course Instructions

Welcome! Please proceed through this course by clicking on the arrows in the upper right or text links on the lower left of the page. Monitor your progress with the Table of Contents, and return to your Student Homepage by clicking on the Home icon. Your progress will be saved automatically as you proceed through the course. If you exit the course, you can continue from where you left off, even if you use a different computer. As you progress through the course, you may find knowledge assessment questions that cover the material you've read so far. These practice questions are not graded or recorded.

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Course Instructions

Welcome! Please proceed through this course by clicking on the arrows in the upper right or text links on the lower left of the page. Monitor your progress with the Table of Contents, and return to your Student Homepage by clicking on the Home icon. Your progress will be saved automatically as you proceed through the course. If you exit the course, you can continue from where you left off, even if you use a different computer. As you progress through the course, you may find knowledge assessment questions that cover the material you've read so far. These practice questions are not graded or recorded.

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Course Info

This course carries the following continuing education credits:

● P.A.C.E. Contact Hours: 1.50 hour(s) Course Number: 578-004-08

● Florida Board of Clinical Laboratory Science CE - General (Microbiology/Mycology/Parasitology): 1.50 hour(s)

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Hyaline Molds

Ungraded Practice Question

Match each hyaline mold from the drop-down list to its corresponding colony and microscopic description. The mold colonies are illustrated in the image on the right.

Select the correct match for each item from the drop-down box

Hyaline Molds



6Choose Colony in upper left quadrant (orange sphere); micoscopic description: Multi-celled, sickle-form macro

6Choose Colony in upper right quadrant (grayish-brown spherical shape); microscopic description: Dark, elliptical conidia each supported by a conidiophore ("lollipops")

6Choose Colony in bottom left quadrant (lilypad-like shape); microscopic description: Chains of spherical conidia produced from branching phialides.

6Choose Colony in bottom right quadrant (green sphere with yellow inner circle); microscopic description: Tight clusters of spherical conidia held by finger-like phialides.


6Choose Fusarium species

Colony in upper left quadrant (orange sphere); micoscopic description: Multi-celled, sickle-form macro

6Choose Scedosporium apiospermum

Colony in upper right quadrant (grayish-brown spherical shape); microscopic description: Dark, elliptical conidia each supported by a conidiophore ("lollipops")

6Choose Penicillium species

Colony in bottom left quadrant (lilypad-like shape); microscopic description: Chains of spherical conidia produced from branching phialides.

6Choose Gliocladium Colony in bottom right quadrant (green sphere with yellow inner circle); microscopic description: Tight clusters of spherical conidia held by finger-like phialides.

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Feedback

The description of "tight clusters of spherical conidia held by finger-like phialides" is the microscopic description for Gliocladium, the colony of which typically appears as a "green lawn" that extends from border to border across the Petri dish.

"Multi-celled, sickle-form macroconidia" is the description for Fusarium species, which produces colonies with a distinctive rose red or purple red pigmentation (upper left).

"Dark, elliptical conidia each supported by a conidiophore ('lollipops')" is characteristic of Scedosporium apiospermum. The grayish-brown appearance of the typical colony is due to the production of darkly pigmented spores as the colony matures.

"Chains of spherical conidia produced from branching phialides" is descriptive of Penicillium species, which typically produces green, granular, rugose colonies.

Hyaline Molds


Match each hyaline mold from the drop-down list to its corresponding microscopic and colony description. The microscopic appearance of the molds are illustrated in the image on the right.


Hyaline Molds


6Choose Microscopic description: Flower-like appearance (Image in the upper left quadrant) Colony description: Green granular colony with a white peripheral apron

6Choose Microscopic description: Stem with bulbous extensions (Image in the upper right quadrant) Colony description: Gray-white, cottony growth rapidly filling the Petri dish

6Choose Microscopic description: Cluster on green background (Image in the lower left quadrant) Colony description: "Green lawn" colony covering the surface of the Petri dish

6Choose Microscopic description: Blue cluster of what look like flowers (Image in the lower right quadrant) Colony description: White, smooth colony with a low downy surface

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Match each hyaline mold from the drop-down list to its corresponding microscopic and colony description. The microscopic appearance of the molds are illustrated in the image on the right.


Feedback

The description of a "gray-white, cottony growth rapidly filling the Petri dish" is characteristic of the Zygomycetes, of which Cunninghamellaspecies is the representative in this exercise. The microscopic features include aseptate hyphae and the production of spherical sporangioles from the surface of a spherical vesicle.

Of the hyaline molds listed in this exercise, "a white, smooth colony with a low downy surface" is consistent with Beuveria species, demonstrated by the loose clusters of tiny conidia, each attached by a "zig zag" conidiophore.

The hyaline mold in this exercise corresponding to a "green granular colony with a white peripheral apron" is the most consistent with Aspergillus fumigatus, microscopically characterized by the production of chains of conidia from a single row of phialides along the top half of a club-shaped vesicle.

A "green lawn" colony covering the surface of the Petri dish points to Trichoderma species among the fungi listed in this exercise, featured microscopically by the production of tight clusters or balls of spherical conidia supported by long, tapered conidiophores.

Hyaline Molds


6Choose Aspergillus fumigatus

Microscopic description: Flower-like appearance (Image in the upper left quadrant) Colony description: Green granular colony with a white peripheral apron

6Choose Zygomycetes Microscopic description: Stem with bulbous extensions (Image in the upper right quadrant) Colony description: Gray-white, cottony growth rapidly filling the Petri dish

6Choose Trichoderma species

Microscopic description: Cluster on green background (Image in the lower left quadrant) Colony description: "Green lawn" colony covering the surface of the Petri dish

6Choose Beuveria species

Microscopic description: Blue cluster of what look like flowers (Image in the lower right quadrant) Colony description: White, smooth colony with a low downy surface

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Hyaline Molds



6Choose Upper left image Multi-celled, rough walled macroconidia with a tapered terminal cell

6Choose Upper right image Dense aggregates of echinulate, brown-black conidia

6Choose Lower left image Loose clusters of elliptical conidia arranged in a "diphtheroid" pattern

6Choose Lower right image Chains of large, lemon-shaped annelloconidia


Feedback

The description of "loose clusters of elliptical conidia arranged in a 'diphtheroid' pattern" is characteristic of Acremonium species, which is represented by the smooth, pastel rose pigmented colony.

"Multi-celled, rough walled macroconidia with a tapered terminal cell" describes the macroconidia of Microsporum canis, the colony of which is usually cottony white with a lemon yellow apron.

"Chains of large, lemon-shaped annelloconidia" describes the microscopic features of Scopulariopsis species, the colony of which is buff-brown with distinctive radial rugae.

6Choose Microsporum canis Upper left image Multi-celled, rough walled macroconidia with a tapered terminal cell

6Choose Aspergillus niger Upper right image Dense aggregates of echinulate, brown-black conidia

6Choose Acremonium species

Lower left image Loose clusters of elliptical conidia arranged in a "diphtheroid" pattern

6Choose Scopulariopsis species

Lower right image Chains of large, lemon-shaped annelloconidia

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"Dense aggregates of echinulate, brown-black conidia" describes Aspergillus niger, the colony of which is a peppered brown-black on the surface and gray-white on the reverse.

Hyaline Molds


Match each of the names of the fungi listed in the left column with its most likely associated disease listed in the right column.


Hyaline Molds


Match each of the names of the fungi listed in the left column with its most likely associated disease listed in the right column.

6Choose Chronic sinusitis

6Choose Otitis externa

6Choose Mycotic keratitis

6Choose Tinea pedis


Feedback

Of the diseases listed in this exercise, Fusarium species is the most likely associated with mycotic keratitis. Trichophyton rubrum is a dermatophyte that commonly causes an itching, scaling skin infection of the feet, known as tinea pedis. Scedosporium apiospermum is commonly associated with sinusitis. Although Aspergillus niger can also be associated with sinusitis in the form of a fungus ball infection, in the context of this exercise, it is the only agent listed that typically causes otitis externa.

Hyaline Molds

6Choose Scedosporium apiospermum Chronic sinusitis

6Choose Aspergillus niger Otitis externa

6Choose Fusarium species Mycotic keratitis

6Choose Trichophyton rubrum Tinea pedis

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Match each of the names of the hyaline molds listed with the environmental conditions or natural objects with which it is most likely associated.


Hyaline Molds


Match each of the names of the hyaline molds listed with the environmental conditions or natural objects with which it is most likely associated.

6Choose Stale bread

6Choose Hospital construction

6Choose Shared bath towels

6Choose Fermenting stored grain


Feedback

Although other hyaline fungi may be found growing on stale bread, of those listed in this exercise, Mucor species is the most likely incriminated.

Aspergillus niger is one of the more frequent molds that contaminate laboratory cultures during times of hospital construction.

Fusarium species commonly grow in fermenting stored grains, producing aflotoxins that can affect any livestock for which the grain may be used as feed.

Epidermophyton floccosum, along with other dermatophytes, may be transmitted from person to person through the use of shared bath towels where spore-infected skin scales are present in profusion.

Hyaline Molds

6Choose Mucor species Stale bread

6Choose Aspergillus niger Hospital construction

6Choose Epidermophyton floccosum Shared bath towels

6Choose Fusarium species Fermenting stored grain

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Match the names of each of the species of hyaline molds listed with the appropriate category.


Hyaline Molds




6Choose Gliocladium species


6Choose Scopulariopsis species


Feedback

Aspergillus species and Scopulariopsis species develop conidia in chains, while the conidia of Gliocladium species and Acremonium species are gathered in tight and loose clusters respectively.

Hyaline Molds



6Choose Conidia in chains Aspergillus fumigatus

6Choose Conidia in clusters Gliocladium species

6Choose Conidia in clusters Acremonium species

6Choose Conidia in chains Scopulariopsis species


6Choose Syncephalastrum species

6Choose Pseudallescheria boydii

6Choose Aspergillus nidulans (telemorph)

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Hyaline Molds



6Choose Mucor species


Feedback

The Zygomycetes, including Syncephalastrum species and Mucor species, typically produce conidia within sack-like sporangia. Of the molds listed in this exercise, Syncephalastrum species produces spores in special cylindrical-shaped sporangia called mesosporangia, and Mucor species develops spores within spherical sporangia; therefore, both of these should be associated with the first category, spores in sporangia.

Cleistothecia are bag like structures containing smaller structures called asci within which ascospores are produced. These are sexual or telomorphic structures that are characteristic of ascosporogenous fungi including Pseudallescheria boydii and certain strains of Aspergillus species, including Aspergillus nidulans.

Hyaline Molds


Match the names of each of the species of hyaline molds listed with the appropriate taxonomic category.

6Choose Spores in sporangia Syncephalastrum species

6Choose Spores in cleistothecia Pseudallescheria boydii

6Choose Spores in cleistothecia Aspergillus nidulans (telemorph)

6Choose Spores in sporangia Mucor species


6Choose Microsporum nanum

6Choose Trichophyton schoenleinii

6Choose Epidermophyton floccosum

6Choose Cunninghamella species

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Hyaline Molds


Match the names of each of the species of hyaline molds listed with the appropriate taxonomic category.


Feedback

Microsporum nanum, Trichophyton schoenleinii and Epidermophyton floccosum are all species of dermatophytes. Cunninghamella species are zygomycetes.

Hyaline Molds


Match the names of each of the fungi listed below into the appropriate category indicating the classification of infection with which it is most commonly associated.

6Choose Dermatophyte Microsporum nanum

6Choose Dermatophyte Trichophyton schoenleinii

6Choose Dermatophyte Epidermophyton floccosum

6Choose Zygomycete Cunninghamella species


Hyaline Molds


Match the names of each of the fungi listed below into the appropriate category indicating the classification of infection with which it is most commonly associated.


6Choose Blastomyces dermatitidis

6Choose Rhizopus species


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Feedback

Most of the hyaline molds are opportunistic pathogens, causing infections only in patients with underlying immunologic, metabolic or hematologic disorders. Aspergillus fumigatus commonly causes infections in patients who are debilitated, immunosuppressed or leukopenic. Rhizopus species is an opportunistic pathogen that may cause invasive infections in patients with diabetes mellitis. Acremonium species is less commonly a pathogen, but may cause post traumatic keratitis and mycetoma.

Blastomyces dermatitidis can cause infections in patients who were previously healthy; therefore, it is an obligate pathogen.

Hyaline Molds


The microscopic features shown in this photomicrograph is of a fungus commonly associated with:

6Choose Opportunistic pathogen Aspergillus fumigatus

6Choose Obligate pathogen Blastomyces dermatitidis

6Choose Opportunistic pathogen Rhizopus species

6Choose Opportunistic pathogen Acremonium species

Please select the single best answer

Hyaline Molds


nmlkj Zygomycosis

nmlkj Aspergillosis

nmlkj Dermatophytosis

nmlkj Pseudallescheriosis

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The microscopic features shown in this photomicrograph is of a fungus commonly associated with:


Feedback

The microscopic features of the fungus seen here, namely, a conidiophore that terminates in a vesicle with a single row of phialides giving rise to chains of conidia, is characteristic of Aspergillus fumigatus, the most common agent of human aspergillosis.

The zygomycetes produce fruiting heads with a vesicle-like columella; however, spores are borne within sack-like sporangia rather than in chains.

None of the dermatophytes produce vesicles or chains of conidia.

Pseudoallescheria boydii produces single celled microconidia and some other species of Pseudoallescheria produce sack-like cleistothecia containing ascospores.

Hyaline Molds


Based on the structures observed in this photomicrograph, the most probable species of the fungus recovered from an induced sputum specimen is:

nmlkj Zygomycosis

nmlkj Aspergillosis

nmlkj Dermatophytosis

nmlkj Pseudallescheriosis


nmlkj Aspergillus fumigatus

nmlkj Aspergillus niger

nmlkj Aspergillus nidulans

nmlkj Aspergillus flavus

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Hyaline Molds


Based on the structures observed in this photomicrograph, the most probable species of the fungus recovered from an induced sputum specimen is:


Feedback

Shown by the red arrow is a vesicle of Aspergillus species, with the production of irregular chains of conidia from phialides that are hidden. The yellow arrow points to a cleistothecium, the telomorphic form that may be produced in clinical isolates by certain strains. Of the Aspergillus species listed, Aspergillus nidulans would be the most likely species with the potential for producing cleistothecia in culture isolates from clinical specimens. In addition, the amorphic fruiting head does not correspond to any of the other species listed.


nmlkj Aspergillus niger

nmlkj Aspergillus nidulans


A. fumigatus produces a distinct single row of phialides, not seen in this photomicrograph, and both Aspergillus flavus and Aspergillus niger sporulate from phialides distributed around the entire circumference of the vesicle.

Hyaline Molds


Illustrated in this photograph is a "green lawn" colony of Gliocladium species. The other hyaline mold that produces this type of colony is:


nmlkj Trichoderma species

nmlkj Paecilomyces species


nmlkj Rhizopus species

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Hyaline Molds


Illustrated in this photograph is a "green lawn" colony of Gliocladium species. The other hyaline mold that produces this type of colony is:


Feedback

Gliocladium species and Trichoderma species are the two hyaline molds that produce this border to border, green lawn colony without a distinct margin. Although both Paecilomyces species and Aspergillus flavus may produce green colonies, they always have a margin, usually with a distinct white apron at the outer margins of new growth.

Rhizopus species also produces a "lawn" like colony that extends from border to border in the Petri dish; however, it never produces a green pigment.

Hyaline Molds


The fungus illustrated in this photomicrograph was recovered from an induced sputum specimen from a 74 year old man with chronic obstructive pulmonary disease. This isolate is most likely:




nmlkj Rhizopus species


nmlkj The cause of chronic bronchitis

nmlkj The cause of invasive pulmonary disease

nmlkj The cause of allergic bronchopulmonary disease

nmlkj A contaminant

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Hyaline Molds


The fungus illustrated in this photomicrograph was recovered from an induced sputum specimen from a 74 year old man with chronic obstructive pulmonary disease. This isolate is most likely:


Feedback

The microscopic features shown here represent Scopulariopsis species. In most instances, particularly if a patient does not have underlying immunologic or hematologic disease, Scopulariopsis species should be considered a contaminant when recovered from a sputum specimen. However, if there is clinical or X-ray evidence of mycotic pulmonary infection, additional daily induced sputum specimens should be obtained.

If Scopulariopsis species or any other hyaline mold is recovered from two or more successive specimens, its potential as a pathogenic agent should be considered. Scopulariopsis species have been reported as the agents of pulmonary fungus ball infections in patients with preexistent cavities and as a cause of pneumonia in patients with leukemia.

Invasive pulmonary disease by this agent has not been reported.

Hyaline Molds


The dermatophytic fungus shown is in this photomicrograph, recovered from a ringworm lesion of the skin of the back of the hand of an 8 year old boy, was most likely contracted from:

nmlkj The cause of chronic bronchitis

nmlkj The cause of invasive pulmonary disease

nmlkj The cause of allergic bronchopulmonary disease

nmlkj A contaminant


nmlkj A commonly used bath towel

nmlkj Soil in the back yard

nmlkj A classmate

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Hyaline Molds


The dermatophytic fungus shown is in this photomicrograph, recovered from a ringworm lesion of the skin of the back of the hand of an 8 year old boy, was most likely contracted from:


Feedback

nmlkj A commonly used bath towel

nmlkj Soil in the back yard

nmlkj A classmate

The photomicrograph illustrates a macroconidium of Microsporum gypseum. M. gypseum is a geophilic fungus that is endemic in the soil. Human to human transfer, either directly or through the use of a common towel, is quite unlikely with M. gypseum.

Hyaline Molds


An Aspergillus species was recovered from a sputum specimen of a patient with X-ray evidence of fungal pneumonia. Microscopic examination did not permit a species identification. A small amount of vegetative mycelium was removed and a direct mount prepared. The features indicated by the red arrows in this image are associated with which Aspergillus species?




nmlkj Aspergillus terreus

nmlkj Aspergillus clavatus

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Hyaline Molds


An Aspergillus species was recovered from a sputum specimen of a patient with X-ray evidence of fungal pneumonia. Microscopic examination did not permit a species identification. A small amount of vegetative mycelium was removed and a direct mount prepared. The features indicated by the red arrows in this image are associated with which Aspergillus species?


Feedback




nmlkj Aspergillus clavatus

Illustrated in this photomicrograph are the spherical, microconidia attached to the vegetative hyphae, a feature unique to Aspergillus terreus. The other Aspergillus species listed in this exercise do not produce these vegetative structures.

Hyaline Molds


The hyaline mold illustrated in this photomicrograph can be identified as:



nmlkj Acremonium species

nmlkj Fusarium species

nmlkj Gliocladium species

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Hyaline Molds


The hyaline mold illustrated in this photomicrograph can be identified as:


Feedback

All of the species listed in this exercise produce microconidia that aggregate in clusters rather than form chains. The clusters of conidia with Gliocladium species are supported by multiple conidiophores as shown in this photomicrograph, much as the cupped fingers would support a tennis ball.

The microconidia of both Fusarium species and Acremonium species are loosely held, are elongated and arrange in an Oriental letter pattern.

The conidia of both Gliocladium species and Trichoderma species are spherical and aggregate in tight clusters or balls. The conidia clusters of Trichoderma species are supported by single, tapered phialides that extend laterally from the hyphae.

Hyaline Molds


The differentiation between Aspergillus species and Scedosporium species may be difficult when only hyphal elements are observed


nmlkj Acremonium species

nmlkj Fusarium species

nmlkj Gliocladium species

in stained tissue sections. It is important to obtain a culture to make this differentiation when possible because Scedosporium species, in contrast to Aspergillus species, tend to be resistant to:


nmlkj Amphotericin B

nmlkj The imidazoles

nmlkj Flucytosine

nmlkj Tolnaftate

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Hyaline Molds


The differentiation between Aspergillus species and Scedosporium species may be difficult when only hyphal elements are observed in stained tissue sections. It is important to obtain a culture to make this differentiation when possible because Scedosporium species, in contrast to Aspergillus species, tend to be resistant to:


Feedback

Since amphotericin B is the antifungal drug most frequently administered empirically in cases of suspected deep and invasive mycoses, it is important to know which fungal agents may have innate resistance to this drug. Most strains of Scedosporium species are resistant to

nmlkj Amphotericin B

nmlkj The imidazoles

nmlkj Flucytosine

nmlkj Tolnaftate

amphotericin B, and administration of one of the imidiazoles is recommended. Most strains of both Aspergillus species and Scedosporium species are resistant to flucytosine; therefore, this agent would not be recommended in the treatment of infections with either of these agents. Tolnaftate is a topical antifungal agent, which would not be appropriate in the treatment of any deep tissue fungal infection.

Hyaline Molds


A dermatophyte that produces thin-walled, two or three-celled macroconidia, and no microconidia, most likely belongs to the genus:


Hyaline Molds


A dermatophyte that produces thin-walled, two or three-celled macroconidia, and no microconidia, most likely belongs to the genus:

nmlkj Microsporum

nmlkj Trichophyton

nmlkj Epidermophyton

nmlkj Ajellomyces

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Feedback

One of the key characteristics in the identification of Epidermophyton floccosum is the inability of this dermatophyte to produce microconidia. Two to four-celled, club-shaped macroconidia are produced, usually in clusters of two or three.

Both Microsporum species and Trichophyton species produce microconidia, the latter genus in profusion.

The genus Ajellomyces does not belong to the dermatophytes; rather is the telomorphic or perfect form of Blastomyces dermatitidis. It produces telomorphic ascocarps that contain ascospores.

Hyaline Molds


The spores produced by telomorphic forms of Aspergillus glaucus are:

nmlkj Microsporum

nmlkj Trichophyton

nmlkj Epidermophyton

nmlkj Ajellomyces


Hyaline Molds


The spores produced by telomorphic forms of Aspergillus glaucus are:

nmlkj Conidia

nmlkj Ascospores

nmlkj Sporangiospsores

nmlkj Chlamydospores


nmlkj Conidia

nmlkj Ascospores

nmlkj Sporangiospsores

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Feedback

The telomorphic forms of Aspergillus glaucus, and other ascosporogenous Aspergillus species, are cleistothecia that contain asci within which are produced ascospores that aggregate in groups of four or eight.

The amorphic sack-like pycnidia, produced by Phoma species, among others, contain conidia. Sporangiospores are produced within sack-like sporangia, the amorphic fruiting heads of the Zygomycetes.

Chlamydospores are derived from the vegetative hyphae and are not contained within any confined structure.

Hyaline Molds


The bare fruiting heads shown here, characteristic of Aspergillus niger, demonstrate a spherical vesicle with phialides positioned around the entire circumference of the surface. The other Aspergillus species that also sporulates circumferentially is:

nmlkj Chlamydospores


Hyaline Molds





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The bare fruiting heads shown here, characteristic of Aspergillus niger, demonstrate a spherical vesicle with phialides positioned around the entire circumference of the surface. The other Aspergillus species that also sporulates circumferentially is:


Feedback

The fruiting heads of Aspergillus flavus are described as having a central spherical vesicle covered on all surfaces by a double row of




sterigmata, consisting of a primary row of metulae and a secondary row of phialides, giving rise to short chains of conidia. Aspergillus clavatus also demonstrates sporulation from the entire surface; however, the vesicles are much larger and typically club-shaped.

The phialides of both Aspergillus fumigatus and Aspergillus terreus are derived from the top portion of the vesicle, and not in the circumferential arrangement as shown here.

Hyaline Molds


A dull white fungus, turning mouse gray on maturity, was recovered from material aspirated from a bone cyst in the upper femur. Based on the microscopic appearance as seen in a lactophenol blue mount of a portion of the colony, the most likely identification is:


nmlkj Scedosporium apiospermum

nmlkj Scedosporium prolificans (inflatum)

nmlkj Sepedonium species

nmlkj Chrysosporium species

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Hyaline Molds


A dull white fungus, turning mouse gray on maturity, was recovered from material aspirated from a bone cyst in the upper femur. Based on the microscopic appearance as seen in a lactophenol blue mount of a portion of the colony, the most likely identification is:


Feedback

Each of the species of fungus listed in this exercise produce single conidia supported by individual conidiophores. The "mouse gray" appearance of the colony suggests that the isolate may be a Scedosporium species, which indeed it is. The flask-shaped swelling in the conidiophore, as illustrated in this photomicrograph, is characteristic of Scedosporium prolificans. The other fungal species listed in this exercise do not form these flask-shaped conidiogenous cells, rather produce straight conidiophores.

Hyaline Molds


The "birds on a fence" arrangement of uniform-sized, tear-shaped microconidia is characteristic of:


nmlkj Scedosporium prolificans (inflatum)




nmlkj Trichophyton tonsurans

nmlkj Trichophyton mentagrophytes

nmlkj Trichophyton rubrum

nmlkj Trichophyton verrucosum

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Hyaline Molds


The "birds on a fence" arrangement of uniform-sized, tear-shaped microconidia is characteristic of:


Feedback

The intended answer is Trichophyton rubrum. Note the tiny microconidia in a "birds on the fence" arrangement along the hyphal strand transversing the field of view (yellow arrows). Two pencil-shaped, smooth walled macroconidia are seen in the lower left field of view (red arrows).

Trichophyton tonsurans may also produce conidia arranged like "birds on the fence"; however, they are irregular in size, with many large club- and balloon-shaped forms present.

"Birds on a fence" microconidia may also be seen with Trichophyton mentagrophytes; however, this is not a constant feature, and is always accompanied by the more typical conidia in clusters.

Although usually in small quantities, Trichophyton verrucosum may produce microconidia. However, they are irregularly arranged with little tendency to line up along the hyphae. Antler hyphae and string bean macroconidia are characteristic of this species.

Hyaline Molds


Illustrated in this photomicrograph are fruiting heads of Trichoderma species. Note the single, long, tapered phialides (red arrows), extending laterally from either side of the hyphae, one of the key identifying features of this fungus. Another hyaline mold that produces long tapered phialides is:

nmlkj Trichophyton tonsurans

nmlkj Trichophyton mentagrophytes

nmlkj Trichophyton rubrum

nmlkj Trichophyton verrucosum


nmlkj Penicillium species


nmlkj Beaveria species

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Hyaline Molds


Illustrated in this photomicrograph are fruiting heads of Trichoderma species. Note the single, long, tapered phialides (red arrows), extending laterally from either side of the hyphae, one of the key identifying features of this fungus. Another hyaline mold that produces long tapered phialides is:


Feedback

The production of long, tapered phialides is one of the key identifying features of Paecilomyces species, in contrast to Penicillium species, in which the ends of the phialides are blunt.

The phialides of Beauveria species are geniculate, forming a zig-zag pattern.

Hyaline Molds


Illustrated here is a single conidium of Microsporum canis. Note that the hilar cell appears fractured (shorter red arrow), where it was released from the stolon. Macroconidia having this so-called "break-away" cell are termed:

nmlkj Penicillium species


nmlkj Beaveria species


nmlkj Ascospsores

nmlkj Dictyospores

nmlkj Aleureospores

nmlkj Arthrospores

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Hyaline Molds


Illustrated here is a single conidium of Microsporum canis. Note that the hilar cell appears fractured (shorter red arrow), where it was released from the stolon. Macroconidia having this so-called "break-away" cell are termed:


Feedback

By definition, an aleureospore is one that becomes detached by the lysis or fracture of the wall of the attachment cell.

Ascospores are single-celled spores formed within sack-like structures called asci.

Dictyospsores are multi-celled macroconidia separated by both longitudinal and transverse septa. A dictyospore may in fact be an aleureospore if it becomes detached by a fractured cell; however, this is not its definition.

Arthrospores are thick, rectangular spores that are derived directly from the vegetative hyphae at points of septation.

Hyaline Molds


The hyaline saprobic fungus that has microscopic features similar to the mold form of Histoplasma capsulatum is:

nmlkj Ascospsores

nmlkj Dictyospores

nmlkj Aleureospores

nmlkj Arthrospores



nmlkj Malbranchia species


nmlkj Scopulariopsis species

Page 30 of 61


Hyaline Molds


The hyaline saprobic fungus that has microscopic features similar to the mold form of Histoplasma capsulatum is:


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Sepedonium species and the mold form of Histoplasma capsulatum share the common microscopic feature of producing large, spherical, single-celled macroconidia that characteristically are covered with echinulations.

Scopulariopsis also produces conidia that may be roughened when mature; however, they are arranged in chains.

Chrysosporium also produces single conidia; however, they are more elliptical and not roughened.

Malbranchia produces rectangular-shaped, alternately staining arthroconidia that have thickened, smooth walls.

Hyaline Molds


The hyaline saprobic fungus that has microscopic features similar to the mold form of Coccidioides immitis is:




nmlkj Scopulariopsis species


Hyaline Molds


nmlkj Geotrichum species

nmlkj Trichosporon species

nmlkj Microsporum canis

Page 31 of 61



The hyaline saprobic fungus that has microscopic features similar to the mold form of Coccidioides immitis is:


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nmlkj Geotrichum species

nmlkj Trichosporon species

nmlkj Microsporum canis

Malbranchia species share the production of alternate staining arthroconidia as a common feature with the mold form of Coccidioides immitis.

Both Geotrichum species and Trichosporon species produce rectangular-shaped arthroconidia; however, they are regularly rather than alternately staining. Additionally, the arthroconidia of Geotrichum may produce germ tubes from one corner and the arthroconidia of Trichosporon species may produce blastoconidia from adjacent corners, features not shared by either Malbranchia species or Coccidioides immitis.

The hyphae of Microsporum canis, as seen in direct KOH mounts of skin scales, may break up into arthroconidia; however, they are much narrower in dimension and do not share the alternate staining characteristics.

Hyaline Molds


Several saprophytic, hyaline molds have microscopic characteristics that mimic the mold forms of the dimorphic fungi (Histoplasma capsulatum, Blastomyces dermatitidis, etc.). Each of the following can be used to differentiate the saprophytic from the dimorphic fungi except:


Hyaline Molds


nmlkj Conversion of the mold form to the yeast form at 37oC incubation

nmlkj Ability of the dimorphic fungi to grow on cycloheximide-containing culture media

nmlkj Differential growth profiles on Trichophyton differential agars

nmlkj Positive reactions for the dimorphic fungi in commercially available nucleic acid probe assays.

Page 32 of 61


Several saprophytic, hyaline molds have microscopic characteristics that mimic the mold forms of the dimorphic fungi (Histoplasma capsulatum, Blastomyces dermatitidis, etc.). Each of the following can be used to differentiate the saprophytic from the dimorphic fungi except:


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Trichophyton differential agars are not intended to differentiate dimorphic from saprophytic fungi and the differences in growth profiles would not be helpful in making this separation.

The dimorphic fungi can be converted to a yeast form by incubation at body temperature, will grow in culture media containing cycloheximide, and will show positive reactions in antigen specific nucleic acid probe assays. All of these procedures can be used to differentiate the saprophytic hyaline mold from the dimorphic fungi.

Hyaline Molds


The most helpful feature in differentiating the Zygomycetes from the other hyaline molds in the clinical mycology laboratory is:

nmlkj Conversion of the mold form to the yeast form at 37oC incubation

nmlkj Ability of the dimorphic fungi to grow on cycloheximide-containing culture media

nmlkj Differential growth profiles on Trichophyton differential agars

nmlkj Positive reactions for the dimorphic fungi in commercially available nucleic acid probe assays.


Hyaline Molds


The most helpful feature in differentiating the Zygomycetes from the other hyaline molds in the clinical mycology laboratory is:

nmlkj Rapid growth rate

nmlkj The production of spores within sporangia

nmlkj The production of rhizoids

nmlkj The formation of aseptate hyphae


nmlkj Rapid growth rate

Page 33 of 61


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The production of spores within sporangia is unique to the Zygomycetes.

Although the production of rhizoids and the formation of aseptate hyphae are characteristics of the Zygomycetes, these are not constant characteristics for all species or at all times during maturation. Only Rhizopus and Absidia species regularly produce rhizoids and occasional septations can be seen in the hyphae of each of the Zygomycetes as the colonies mature, particularly in the sporangiophores.

Although the rate of growth of the Zygomycetes is among the more rapid among the fungi, many strains of Aspergillus species and other hyaline fungi may also grow within the 2-3 day period.

Dematiaceous Molds


Match each of the names of the fungal species listed with the corresponding identifying structures illustrated in the photomicrographs:

nmlkj The production of spores within sporangia

nmlkj The production of rhizoids

nmlkj The formation of aseptate hyphae


Dematiaceous Molds


6Choose A

6Choose B

6Choose C

6Choose D

Page 34 of 61


Match each of the names of the fungal species listed with the corresponding identifying structures illustrated in the photomicrographs:


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Stemphylium species microscopically are characterized by the production of dark brown, oblong or broadly elliptical, multi-celled, muriform conidia that are supported by a straight conidiophore (so-called "bale of cotton on a stick") (upper left).

Bipolaris species produce smooth-walled, oblong-shaped, multi-celled conidia (lower left) with the individual cells surrounded and separated by a sac-like wall called a distosepta that is not part of the cell wall. The macroconidia are borne sympodially from bent, geniculate conidiophores.

The macroconidia of Curvularia species have cells separated by true septa extending from the cell wall. The multi-celled, dark brown, macroconidia are bow- or boomerang-shaped due to overgrowth of the central cells (upper right).

The macroconidia of Alternaria species are muriform, are elongated and drumstick shaped, and are connected together in chains, with the blunt end of one conidium attached to the narrow end of another (lower right).

Dematiaceous Molds


Match the names of each of the fungal species listed in the drop-down box with the corresponding identifying structures illustrated in the photomicrographs:

6Choose Stemphylium species A

6Choose Curvularia species B

6Choose Bipolaris species C

6Choose Alternaria species D


6Choose Upper left

6Choose Upper right

6Choose Lower left

6Choose Lower right

Page 35 of 61


Dematiaceous Molds


Match the names of each of the fungal species listed in the drop-down box with the corresponding identifying structures illustrated in the photomicrographs:


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Exserohilum species produce long, pencil-shaped, multi-celled macroconidia in which the individual cells are separated by a sac-like wall that is not part of the outer cell wall; structures called distosepta (lower left). The distinguishing feature, as reflected in the genus name, is the distinct nipple-like extension from the hilar cell, which serves as a point of attachment to the conidiophore.

Nigrospora species microscopically produce single-celled, jet black, globose conidia, each supported by a short pedicle with a swollen base (lower right).

Epicoccum species can be recognized microscopically by the production of dark brown, club-shaped, multi-celled muriform macroconidia that are attached laterally either directly from the hyphae or from short conidiophores and aggregate in tight clusters (upper left).

Ulocladium produces subglobose, muriform macroconidia that are borne sympodially from bent, geniculate conidiophores (upper right).

Dematiaceous Molds


6Choose Epicoccum species Upper left

6Choose Ulocladium species Upper right

6Choose Exserohilum species Lower left

6Choose Nigrospora species Lower right

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A presumptive identification of the four genera of slower growing pathogenic dematiaceous molds can be made by observing specific types of conidiation. Match the names of the species of dematiaceous pathogenic fungi with the corresponding microscopic features illustrated in the photomicrographs:


Dematiaceous Molds


A presumptive identification of the four genera of slower growing pathogenic dematiaceous molds can be made by observing specific types of conidiation. Match the names of the species of dematiaceous pathogenic fungi with the corresponding microscopic features illustrated in the photomicrographs:

6Choose Upper left

6Choose Upper right

6Choose Lower left

6Choose Lower right


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Phialophora type sporulation, typical of Phialophora verrucosum, is characterized by short urn-shaped phialides, each with a narrow mouth from which spherical conidia in tight ball-like aggregates are released (upper left).

The cladosporium type sporulation, represented in the upper right photomicrograph by Cladosporium carrionii in this exercise, is characterized by the production of uniform-sized, oval or elliptical-shaped conidia that are produced in chains from the tips of branching conidiophores. Dark staining scars or collarettes are seen connecting adjacent conidia.

Exophiala jeanselmei (lower left) produces long tapered phialides from the tips of which are released oval to elliptical conidia that aggregate in loose clusters or fall down the sides of the phialides.

The sporulation in the lower right photomicrograph, characteristic of Fonsecaea pedrosoi, is acrotheca in type, characterized by the production of short chains of elliptical conidia borne radially from the sides of hyphae.

6Choose Phialophora verrucosum Upper left

6Choose Cladosporium carrionii Upper right

6Choose Exophiala jeanselmei Lower left

6Choose Fonsecaea pedrosoi Lower right

Page 37 of 61


Dematiaceous Molds


Match the name of each dematiaceous fungus listed in the drop-down box with its most likely disease.


Dematiaceous Molds


Match the name of each dematiaceous fungus listed in the drop-down box with its most likely disease.

6Choose Brain abscess

6Choose Chronic sinusitis

6Choose Chromomycosis

6Choose Subcutaneous Phaeohyphomycotic cyst


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6Choose Cladosporium trichoides (Xylohypha bantianum)

Brain abscess

6Choose Bipolaris species Chronic sinusitis

6Choose Phialophora verrucosum Chromomycosis

6Choose Phialophora richardsiae Subcutaneous Phaeohyphomycotic cyst

Of the answers listed in this exercise, Bipolaris species is most commonly associated with sinusitis. Although both Phialophora verrucosum and Phialophora richardsiae can be involved in subcutaneous mycetomas, the latter is more commonly associated with the formation of phaeohyphomycotic cysts.

Cladosporium trichoides, currently named Xylohypha bantianum, is the most common isolate of this group of fungi from cases of mycotic cerebral abscess.

Phialophora verrucosum among the group of fungi listed in this exercise, is the more likely agent of the exophytic cutaneous lesions called chromomycosis.

Page 38 of 61


Dematiaceous Molds


Match the name of each fungal species listed with its most likely corresponding morphologic features.


Dematiaceous Molds


Match the name of each fungal species listed with its most likely corresponding morphologic features.

6Choose Polar germ tubes

6Choose Dictyospores

6Choose Urn-shaped phialides

6Choose Black yeast colony


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Alternaria species is characterized by the production of drum stick-shaped multi-celled, muriform macroconidia called dictyospores.

The identifying characteristic of Aureobasidium pullulans is the production of a black yeast-like colony.

Bipolaris species receives its genus name from the production of germ tubes extending from both sides of a conidium that has been incubated in an aqueous environment for several hours.

The production of urn-shaped phialides is characteristic of Phialophora verrucosum.

Dematiaceous Molds


6Choose Bipolaris species Polar germ tubes

6Choose Alternaria species Dictyospores

6Choose Phailophora verrucosum Urn-shaped phialides

6Choose Aureobasidium pullulans Black yeast colony

Page 39 of 61


Match the name of each fungal species listed in the drop-down box with its most likely corresponding morphologic feature.


Dematiaceous Molds


Match the name of each fungal species listed in the drop-down box with its most likely corresponding morphologic feature.

6Choose Hilar cell extension

6Choose Sporodochium

6Choose Rhinocladiella type sporulation

6Choose Macroconidia with enlarged center cells


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Certain strains of Fonsecaea pedrosoi produce the rhinocladiella type of sporulation, in which single-celled oval to elliptical conidia are borne sympodially from the sides and tips of straight phialides.

The macroconidia of Curvularia species are multi-celled and divided by transverse septa. Overgrowth of the central cells results in a boomerang shape.

Excerohilum species are characterized by the production of nipple-like extension from the hilar cell. The dark-staining, muriform macroconidia of Epicoccum species are produced from the sides of the hyphae in compact clusters, an arrangement known as a sporodochium.

Dematiaceous Molds


Match the names of each of the fungi listed with its appropriate category.

6Choose Exserohilum species Hilar cell extension

6Choose Epicoccum species Sporodochium

6Choose Fonsecaea pedrosoi Rhinocladiella type sporulation

6Choose Curvularia species Macroconidia with enlarged center cells


Page 40 of 61


Dematiaceous Molds


Match the names of each of the fungi listed with its appropriate category.

6Choose Phialophora verrucosa

6Choose Alternaria species

6Choose Exophiala species

6Choose Cladosporium species


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The conidia of Phialophora verrucosa and Exophiala species are produced within phialides that extrude the conidia in tight, ball-like clusters.

The large, drum stick-shaped muriform macroconidia of Alternaria species are arranged in short chains; the small, elliptical conidia of Cladosporium species are arranged in both long and short, branching chains.

Dematiaceous Molds


Match the names of each of the fungi listed with its appropriate category depending upon whether the multi-celled macroconidia are divided by both longitudinal and transverse septa (dictyospores); or, are divided by only transverse septa.

6Choose Conidia in clusters Phialophora verrucosa

6Choose Conidia in chains Alternaria species

6Choose Conidia in clusters Exophiala species

6Choose Conidia in chains Cladosporium species


6Choose Exserohilum species

6Choose Epicoccum species

6Choose Curvularia species

6Choose Ulocladium species

Page 41 of 61


Dematiaceous Molds


Match the names of each of the fungi listed with its appropriate category depending upon whether the multi-celled macroconidia are divided by both longitudinal and transverse septa (dictyospores); or, are divided by only transverse septa.


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Dictyospores are multi-celled muriform macroconidia in which the cells are divided by both longitudinal and transverse septa. Epicoccum species and Ulocladium species each produce this type of macroconidium.

Of the fungi listed in this exercise, Curvularia, and Exserohilum produce multi-celled macroconidia in which the individual cells are divided by transverse septa only.

Dematiaceous Molds


Match the names of each of the fungi listed with its appropriate category indicating the degree of pathogenicity.

6Choose Transverse septa Exserohilum species

6Choose Dictyospores Epicoccum species

6Choose Transverse septa Curvularia species

6Choose Dictyospores Ulocladium species


6Choose Alternaria species

6Choose Fonsecaea pedrosoi

6Choose Phialophora verrucosa

6Choose Bipolaris species

Page 42 of 61


Dematiaceous Molds


Match the names of each of the fungi listed with its appropriate category indicating the degree of pathogenicity.


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It may be concluded that there is no truly non pathogenic fungus as any species may cause an infection in severely immunocompromised patients. However, some fungi have more innate capabilities of causing infections than others.

Of the fungi listed in this exercise, Fonsecaea pedrosoi and Phialophora verrucosa, each serving as agents of chromomycosis, are generally considered "pathogenic" species.

Alternaria species and Bipolaris species are usually not pathogenic, but may cause opportunistic infections in debilitated patients, commonly sinusitis from the inhalation of spore-laden dust; or, subcutaneous mycetomas where spore-infected vegetative material has been traumatically inoculated into the skin.

Dematiaceous Molds


The fungal species most likely associated with the granulomatous infection seen in this photomicrograph, illustrating segmented, dark brown-staining grains with a giant cell is:

6Choose Usually not pathogenic Alternaria species

6Choose Usually pathogenic Fonsecaea pedrosoi

6Choose Usually pathogenic Phialophora verrucosa

6Choose Usually not pathogenic Bipolaris species


nmlkj Phialophora verrucosum


nmlkj Sporothrix schenckii

nmlkj Exserohilum species

Page 43 of 61


Dematiaceous Molds


The fungal species most likely associated with the granulomatous infection seen in this photomicrograph, illustrating segmented, dark brown-staining grains with a giant cell is:


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The segmented dark-staining grains seen in this photomicrograph are most commonly seen in cases of chromomycosis. Of the fungal species listed in this exercise, only Phialophora verrucosum is associated with chromomycosis and has the capability of producing the grains seen in the photograph.

Although Scedosporium apiospermum may cause mycetoma and produce grains, they are soft, gray white and not segmented.

Sporothrix schenckii is the agent of subcutaneous sporotrichosis, an infection that may result in granulomatous inflammation with the presence of multi-nucleated giant cells; however, grains or granules are not formed.

Exserohilum species are soil dematiaceous molds that rarely may be involved in subcutaneous mycetomas; however, it is not associated with chromomycosis and does not produce grains.

Dematiaceous Molds


The infrequently encountered mold that is represented by the photomicrograph begins as a gray-white colony that blackens with maturity as the hyphae become darkened and single, globose, black conidia are produced. This fungus can be identified as:



nmlkj Sporothrix schenckii



nmlkj Pseudallescheria boydii

nmlkj Nigrospora species

nmlkj Scopulariopsis brumptii

nmlkj Stemphilium species

Page 44 of 61


Dematiaceous Molds


The infrequently encountered mold that is represented by the photomicrograph begins as a gray-white colony that blackens with maturity as the hyphae become darkened and single, globose, black conidia are produced. This fungus can be identified as:


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Each of the fungal species listed here produces colonies that may darken with maturity; however, only Nigrospora species produce the single, globose, black conidia described in the question.

The anamorphic conidia of Pseudallescheria boydii are also produced singly and darken with maturity; however, are small and never turn "black".

The conidia of Scopulariopsis brumptii are lemon-shaped, annelloconidia arranged in chains and the macroconidia of Stemphylium species, although borne singly, are multi-celled and muriform in appearance.

Dematiaceous Molds


nmlkj Pseudallescheria boydii




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The multi-celled conidia of this dematiaceous mold are divided into cells by what are called distosepta (pseudosepta), indicating that the individual cells are surrounded by a sac-like wall that is distinct from the outer cell wall of the conidium. The identification of this mold is:


Dematiaceous Molds


The multi-celled conidia of this dematiaceous mold are divided into cells by what are called distosepta (pseudosepta), indicating that the individual cells are surrounded by a sac-like wall that is distinct from the outer cell wall of the conidium. The identification of this mold is:

nmlkj Curvularia species



nmlkj Bipolaris species


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The multi-celled macroconidia shown in this photomicrograph are those of Bipolaris species. Note the thickened, sac-like structures surrounding the central, spherical cells. These are in contrast to the distinct septa derived from the cell wall as seen with Curvularia species.

Exserohilum species also produce macroconidia with distosepta; however, in contrast to the macroconidia of Bipolaris species, they are long and pencil-shaped and show a prominent nipple-like protrusion from the hilar cell, which serves as the point of attachment to the hyphae.

Stemphylium species produce multi-celled, muriform, macroconidia separated by both longitudinal and transverse septa (dictyospores).





Page 46 of 61


Dematiaceous Molds


The oval or curved multi-celled, dark-staining macroconidia divided by transverse septa only is characteristic of:


Dematiaceous Molds


The oval or curved multi-celled, dark-staining macroconidia divided by transverse septa only is characteristic of:

nmlkj Drechslera species



nmlkj Alternaria species


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The boomerang-shaped macroconidia of Curvularia species are divided by transverse, true septations only. The curved or boomerang effect is caused by overgrowth of the central cells (arrows). The macroconidia of Exserohilum species also have cells divided by transverse septa only, although the septa are false and are called distosepta because they are not derived from the cell walls. These conidia are also long and pencil-shaped and have a prominent nipple like protrusion from the hilar cell. The macroconidia of Drechslera species are muriform and show both longitudinal and transverse septation. The drum stick-shaped macroconidia of Alternaria species also are divided by both longitudinal and transverse septa.





Page 47 of 61


Dematiaceous Molds


The type of sporulation of the dematiaceous mold that is illustrated in this photomicrograph is called:


Dematiaceous Molds


The type of sporulation of the dematiaceous mold that is illustrated in this photomicrograph is called:

nmlkj Acrotheca

nmlkj Rhinocladiella

nmlkj Birds on a fence

nmlkj Acropetal


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The production of single conidia in succession both laterally and around the tip of a straight phialide is called the rhinocladiella type of sporulation, characteristic of Fonsecaea pedrosoi.

Acrotheca type sporulation is also produced by F. pedrosoi; however, is characterized by the production of short chains of elliptical conidia in a circular arrangement from the tips of branching phialides.

nmlkj Acrotheca

nmlkj Rhinocladiella

nmlkj Birds on a fence

nmlkj Acropetal

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The "birds on a fence" arrangement of microconidia, characteristic of Trichophyton rubrum, is somewhat reminiscent of the rhinocladiella type sporulation except that the conidia are more loosely held and alternate more from one side of the hyphae to the other. (T. rubrum is a hyaline rather than a dematiaceous fungus.)

Acropetal is the term referring to a type of sporulation where chains of conidia are formed with each new daughter cell produced from the previous one, leaving the oldest cell at the base of the chain. This type of sporulation is characteristic of Aspergillus species and Penicillium species.

Dematiaceous Molds


Of the following dematiaceous fungi, the black, suede-like colony illustrated here, reaching no larger than the size of a dime after 7 days incubation, most likely can be identified as:


Dematiaceous Molds




nmlkj Fonsecaea species


Page 49 of 61


Of the following dematiaceous fungi, the black, suede-like colony illustrated here, reaching no larger than the size of a dime after 7 days incubation, most likely can be identified as:


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The dematiaceous molds can be broadly separated into two major groups: the agents of chromomycosis that grow more slowly, maturing only after 7 days or more of incubation, and the more rapidly growing species that most commonly are clinically insignificant commensals or contaminants when recovered from clinical specimens, but in rare situations may cause opportunistic infections called phaeohyphomycosis. Of the species of dematiaceous fungi listed in this exercise, only Fonsecaea species fits the slow growth characteristics indicated in the question. All others listed will produce relatively large, mature colonies within 7 days of incubation.

Dematiaceous Molds


The dematiaceous colony illustrated here grew to a diameter of 3 - 4 cm in 5 days. The dematiaceous fungus that can be ruled out is:



nmlkj Fonsecaea species



Dematiaceous Molds





nmlkj Ulocladium species

Page 50 of 61


The dematiaceous colony illustrated here grew to a diameter of 3 - 4 cm in 5 days. The dematiaceous fungus that can be ruled out is:


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Of the species of dematiaceous fungi listed in this exercise, all grow rapidly, forming mature colonies within 5-7 days of incubation, except for Phialophora verrucosum, one of the agents of chromomycosis, which grows more slowly, producing colonies no more than 1 cm in diameter after 7 days incubation.

The dematiaceous molds can be broadly separated into two major groups: the agents of chromomycosis that grow more slowly, maturing only after 7 days or more of incubation, and the more rapidly growing species that most commonly are clinically insignificant commensals or contaminants when recovered from clinical specimens. However, in rare situations, they may cause opportunistic infections called phaeohyphomycosis.

Dematiaceous Molds


The dematiaceous fungus that may produce both acrotheca and rhinocladiella types of sporulation is:




nmlkj Ulocladium species


Dematiaceous Molds


The dematiaceous fungus that may produce both acrotheca and rhinocladiella types of sporulation is:

nmlkj Fonsecaea pedrosoi

nmlkj Exophiala jeanselmei

nmlkj Phialophora richardsiae

nmlkj Aureobasidium pullulans


nmlkj Fonsecaea pedrosoi

Page 51 of 61


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The four genera of slowly growing dematiaceous molds that cause chromomycosis and mycetoma can be differentiated by their unique forms of sporulation. Of these, Fonsecaea pedrosoi is the only species that may exhibit each of the various types of sporulation. The acrotheca and rhinocladiella forms of sporulation are unique to this species and predominate in most strains. Acrotheca type sporulation appears as single or short chains of elliptical conidia that come off the hypha circumferentially, much as the hooks on a hat rack. Rhinocladiella type sporulation consists of single conidia festooned on either side of a straight conidiophore.

Exophiala jeanselmei produces a long tapered phialide with clusters of elliptical conidia at the tip.

Phialophora richardsiae produces flask-shaped phialides that terminate in a flat saucer-like lip which supports clusters of conidia.

Aureobasidium pullulans produces large, dark, arthroconidia-like thickenings of the hyphae at points of septation, from which bud off small, elliptical hyaline microconidia.

Dematiaceous Molds


Saprophytic Cladosporium species may be difficult to differentiate from Cladosporium trichoides (Xylohypha bantianum) in culture as




both produce chains of conidia separated by distinct scars or dysjuncters. Each of the following characteristics of Cladosporium trichoides are helpful in separating the two except:


Dematiaceous Molds


Saprophytic Cladosporium species may be difficult to differentiate from Cladosporium trichoides (Xylohypha bantianum) in culture as

nmlkj Slow growth rate

nmlkj Neurotropism in animal experiments

nmlkj Ability to grow at 43oC

nmlkj Conversion to a yeast form

both produce chains of conidia separated by distinct scars or dysjuncters. Each of the following characteristics of Cladosporium trichoides are helpful in separating the two except:


Page 52 of 61


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Neither saprophytic Cladosporium species nor Cladosporium trichoides (Xylohypha bantianum) convert to yeast forms; this is not a differential characteristic and therefore is the correct answer.

Xylohypha bantianum, formerly called Cladosporium trichoides, has a special nitch with the dematiaceous pathogenic fungi in being selectively associated with cerebral abscesses; therefore, its definitive laboratory identification may be important. This neurotropism in humans has also been demonstrated in experimental animals. The ability to grow at 43°C and to liquify gelatin are two additional characteristics by which X. bantianum can be differentiated from saprophytic Cladosporium species.

Dematiaceous Molds


The black yeast colony illustrated in this photograph may represent any of the following dematiaceous molds except:

nmlkj Slow growth rate

nmlkj Neurotropism in animal experiments

nmlkj Ability to grow at 43oC

nmlkj Conversion to a yeast form


Dematiaceous Molds


nmlkj Phaeoannellomyces wernickii

nmlkj Exophiala jeanselmei (young colony)



Page 53 of 61


The black yeast colony illustrated in this photograph may represent any of the following dematiaceous molds except:


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Of the fungal species listed in this exercise, Scopulariopsis brumptii is the only one that does not have a yeast form during any part of its growth cycle.

Aureobasidium pullulans and Phaeoannellomyces wernickii characteristically produce black yeasts throughout their maturation process. The young colonies of Exophiala jeanselmei may appear as a black yeast, being microscopically identical to P. wernickii.

Dematiaceous Molds


The chain of conidia illustrated in this photomicrograph, with the deep-staining truncated bases, are called annelloconidia, and are most characteristic of:


nmlkj Exophiala jeanselmei (young colony)




Dematiaceous Molds


nmlkj Cladosporium species




Page 54 of 61


The chain of conidia illustrated in this photomicrograph, with the deep-staining truncated bases, are called annelloconidia, and are most characteristic of:


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nmlkj Cladosporium species




The dematiaceous variant of Scopulariopsis species is called Scopulariopsis brumptii. True to the genus, conidiation is through the production of chains of relatively large lemon-shaped conidia, with thicker, more darkly staining truncated bases, representing scars or annellides. Therefore, they are called annelloconidia.

Cladosporium species also produce conidia in chains with darker staining dysjunctors between the cells. However, these conidia are relatively small and elliptical in shape.

The conidia of Alternaria species are also in chains; however, they are quite large and muriform in type, with multiple cells divided by both longitudinal and transverse septation.

Aureobasidium pullulans produces tiny, hyaline microconidia that bud from the thickened arthroconidia-like segments of the hyphae.

Dematiaceous Molds


In this photomicrograph are observed several background dematiaceous hyphae within which is seen a long, flask-shaped, tapered phialide (arrow) that has a flat saucer-like terminus. This feature is most characteristic of:


nmlkj Phialophora verrucosa




Page 55 of 61


Dematiaceous Molds


In this photomicrograph are observed several background dematiaceous hyphae within which is seen a long, flask-shaped, tapered phialide (arrow) that has a flat saucer-like terminus. This feature is most characteristic of:


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The microscopic structures that are described in the question and are illustrated in the photomicrograph are characteristic of Phialophora richardsiae.

Exophiala jeanselmei produces a long, slender, tapered phialide that may appear roughened at the tip where the rings or annellides have formed.

The conidia of Scopulariopsis brumptii are lemon-shaped and have a flat, truncated base, rather than the open phialides seen with these other species.

Dematiaceous Molds


The disease with which the dematiaceous fungus illustrated in this photomicrograph is most likely associated is:

nmlkj Phialophora verrucosa





nmlkj Chronic sinusitis

nmlkj Brain abscess

nmlkj Invasive pulmonary mycosis

nmlkj Subcutaneous mycetoma

Page 56 of 61


Dematiaceous Molds


The disease with which the dematiaceous fungus illustrated in this photomicrograph is most likely associated is:


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The dematiaceous fungus illustrated in this photomicrograph has the microscopic characteristics of Curvularia species. Curvularia species are most commonly considered as laboratory contaminants or commensals; however, of the diseases listed in this exercise, they may occasionally cause sinusitis in patients with underlying disease.

nmlkj Chronic sinusitis

nmlkj Brain abscess

nmlkj Invasive pulmonary mycosis

nmlkj Subcutaneous mycetoma

Brain abscesses are more commonly caused by Cladosporium (Xylohypha) bantianum.

Invasive pulmonary mycosis is a rare condition for any of the dematiaceous fungi and subcutaneous mycetomas would be more likely caused by Exophiala or Phialophora species, although Curvularia species in rare instances could cause mycetoma if spore-contaminated vegetative material had been directly inoculated into the deep skin.

Dematiaceous Molds


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The dematiaceous conidium illustrated in this photomicrograph was obtained from a tiny portion of dark colony that grew to maturity in six days. Spores incubated in a saline mount for four hours developed germ tubes from both terminal cells. The features observed confirm the identification of:


Dematiaceous Molds


The dematiaceous conidium illustrated in this photomicrograph was obtained from a tiny portion of dark colony that grew to maturity in six days. Spores incubated in a saline mount for four hours developed germ tubes from both terminal cells. The features observed confirm the identification of:






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The genus name Bipolaris is derived from its characteristic production of germ tubes on either end of the cell upon incubation in water or physiologic saline for a few hours.

The closely related Drechslera species also produce germ tubes upon incubation; however, they are single and emerge only from the hilar cell at a right angle.

The conidia of Curvularia species and Exserohilum species do not produce germ tubes of any type when incubated in an aqueous atmosphere.





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Dematiaceous Molds


The chief microscopic feature possessed by Ulocladium species by which it can be differentiated from the close look-alike Stemphilium species is:


Dematiaceous Molds


The chief microscopic feature possessed by Ulocladium species by which it can be differentiated from the close look-alike Stemphilium species is:

nmlkj Dematiaceous septate hyphae

nmlkj The production of annelloconidia in chains

nmlkj The production of dictyospores

nmlkj The presence of geniculate conidiophores


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In any given culture, it is often difficult to differentiate Ulocladium species from Stemphylium species, to the extent that these may represent variants of the same species. The chief differential features between the two is the production of bent or geniculate conidiophores by Ulocladium species, while the conidia of Stemphylium species are borne from the tips of straight conidiophores (so called a "bale of cotton" on a stick).

The problem arises when both forms of sporulation occur in the same culture. In such instances, one can only judge the species by which of these two forms of sporulation predominate.

The other features listed in this exercise will not differentiate the two species, as both have dematiaceous, septate hyphae and neither produce muriform macroconidia (dictyospores) or conidia in chains.

nmlkj Dematiaceous septate hyphae

nmlkj The production of annelloconidia in chains

nmlkj The production of dictyospores

nmlkj The presence of geniculate conidiophores

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Dematiaceous Molds


The etiologic agent of the superficial skin infection tinea niger palmaris (plantaris) is:


Dematiaceous Molds


The etiologic agent of the superficial skin infection tinea niger palmaris (plantaris) is:



nmlkj Cladosporium trichoides (Xylohypha bantianum)



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The black yeast, now called Phaeoannellomyces wernickii, the cause of tinea nigra palmaris, has had a number of name changes through the years, previously being included at one time or another in genera Cladosporium, Dematium, and Exophiala. The current genus name, Phaeoannellomyces (dark fungus producing annellides) derives from the microscopic appearance in young cultures of the two-celled, spindle-shaped yeast cells that are divided centrally by a distinct, dark brown or black dysjunctor or scar known as an annellide. As the colony matures, a distinct dematiaceous mycelium develops often producing fruiting bodies similar to those produced by members of the genus Exophiala. Some mycologists believe that Phaeoannellomyces wernickii is a synanamorph of Exophiala species.



nmlkj Cladosporium trichoides (Xylohypha bantianum)


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