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A3 - Microbiology - Harr > 8.9 Mycology > Flashcards

8.9 Mycology Flashcards

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1
Q

All of the following are examples of appropriate specimens for the recovery of fungi except:
A. Tissue biopsy
B. Cerebrospinal fluid
C. Aspirate of exudate
D. Swab

A

D. Swab

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2
Q

For which clinical specimens is the KOH direct mount technique for examination of fungal elements used?
A. Skin
B. Cerebrospinal fluid
C. Blood
D. Bone marrow

A

A. Skin

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3
Q

The India ink stain is used as a presumptive test for the presence of which organism?
A. Aspergillus niger in blood
B. Cryptococcus neoformans in CSF
C. Histoplasma capsulatum in CSF
D. Candida albicans in blood or body fluids

A

B. Cryptococcus neoformans in CSF

Meningitis caused by C. neoformans is diagnosed through culture, biochemical reactions, and rapid agglutination tests for cryptococcal antigen. The India ink test is not diagnostic for cryptococcal meningitis because positive staining results are demonstated in less than 50% of confirmed cases. A positive India ink test shows yeast cells in CSF with a surrounding clear area (the capsule) because the capsule of C. neoformans is not penetrated by ink particles.

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4
Q

Cutaneous disease involving skin, hair, and nails usually indicates an infections with a:
A. Dimorphic fungus
B. Dermatophyte
C. Mucorales (previously Zygomycetes)
D. Candida species

A

B. Dermatophyte

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5
Q

What is the first step to be performed in the identification of an unknown yeast isolate?
A. Gram staining
B. India ink staining
C. Catalase test
D. Germ tube test

A

D. Germ tube test

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6
Q

An isolate produced a constriction that was interpreted as a postive gram tube, but C. albicans was ruled out when confirmatory tests were performed. Which of the following fungi is the most likely identification?
A. Candida tropicalis
B. Crytococcus neoformans
C. Candida glabrata
D. Rhodotorula rubra

A

Footnote

A. Candida tropicalis’

C. tropicalis forms pseudohyphae that resemble true germ tubes by producing a constriction at the point of origin of the yeast cell. Germ tubes represent true hyphae without constriction, and therefore the test should have been repeated along with carbohydrate test before making a presumptive identification. The other three species of yeast listed do not form hyphae.

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7
Q

Cornmeal agar with Tween 80 is used to identify which characteristic of an unknown yeast isolate?
A. Hyphae (true and pseudo)
B. Blastoconidia and arthroconidia
C. Chlamydoconidia
D. All of these options

A

D. All of these options

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8
Q

Blastoconidia are the beginning of which structures?
A. Arthroconidia
B. Germ tubes
C. Pseudohyphae
D. True hyphae

A

C. Pseudohyphae

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9
Q

An isolate from CSF growing on cornmeal agar produces the following structures:
Blastoconidia = +
Pseudohyphae = Neg
Chlamydoconidia = Neg
Arthroconidia = Neg

Which tests should be performed next?
A. Birdseed agar and urease
B. Germ tube and glucose
C. India ink and germ tube
D. All of these options

A

A. Birdseed agar and urease

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10
Q

Which of the following yeast enzymes is detected using birdseed (niger seed) agar?
A. Phenol oxidase
B. Catalase
C. Urease
D. Nitrate reductase

A

A. Phenol oxidase

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11
Q

Which of the following yeasts is characteristically positive for germ tube production?
A. Candida tropicalis
B. Candida kefyr (pseudotropicalis)
C. Cryptococcus neoformans
D. Candida albicans

A

D. Candida albicans

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12
Q

Arthroconidia production is used to differentiate which two yeast isolates?
A. Candida albicans and Candida dubliniensis
B. Trichosporon cutaneum and Cryptococcus neoformans
C. Candida albicans and Candida tropicalis
D. Saccharomyces cerevisiae and Candida glabrata

A

B. Trichosporon cutaneum and Cryptococcus neoformans

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13
Q

The urease test, niger seed agar test, and the germ tube test are all used for the presumptive identification of:
A. Rhodotorula rubra
B. Cryptococcus neoformans
C. Trichosporon cutaneum
D. Candida albicans

A

B. Cryptococcus neoformans

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14
Q

Which of the following yeasts produces only blastoconidia on cornmeal Tween 80 agar?
A. Candida spp.
B. Trichosporon spp.
C. Geotrichum spp.
D. Cryptococcus spp.

A

D. Cryptococcus spp.

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15
Q

Ascospores are formed by which yeast isolate?
A. Saccharomyces cerevisiae
B. Candida albicans
C. Cryptococcus neoformans
D. All of these options

A

A. Saccharomyces cerevisiae

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16
Q

A germ tube-negative, pink yeast isolate was recovered from the respiratory secretions and urine of a patient with AIDS. Given the following results, what is the most likely identification?
CORNMEAL TWEEN 80 AGAR
Blastoconidia = +
Pseudohyphae = Neg
Arthroconidia = Neg
Urease = +
A. Candida albicans
B. Rhodotorula spp.
C. Crytococcus spp.
D. Trichosporon spp.

A

B. Rhodotorula spp.

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17
Q

Terminal chlamydoconidia production is demonstrated by which Candida species?
A. Candida glabrata
B. Candida krusei
C. Candida albicans
D. Candida tropicalis

A

C. Candida albicans

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18
Q

Carbohydrate assimilation tests are used for identification of yeast isolates by inoculating media:
A. Free of carbohydrates
B. Free of niger seed
C. Containing carbohydrates
D. Containing yeast extract

A

A. Free of carbohydrates

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19
Q

Yeast recovered from the urine of a catheterized patient receiving chemotherapy for cancer gave the following results:
CORNMEAL TWEEN 80 AGAR
Germ tube = +
Blastoconidia = +
Pseudohyphae = +
Arthroconidia = Neg
Terminal chlamydoconidia = +

What further testing is necessary?
A. Carbohydrate assimilation and urease
B. Urease and niger seed
C. Nitrate reductase and carbohydrate fermentation
D. No further testing is needed for identification

A

D. No further testing is needed for identification

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20
Q

A blood agar plate inoculated with sputum from a patient with diabetes mellitus grew very few bacterial flora and a predominance of yeast. Given the following results, what is the most likely identification of the yeast isolate?
CORNMEAL TWEEN 80 AGAR
Germ tube = Neg
Pseudohyphae = +
Arthroconidia = Neg
Blastoconidia = + (arranged along pseudohyphae)
Chlamydoconidia = Neg
__________________________
A. Candida tropicalis
B. Candida kefyr (pseudotropicalis)
C. Trichosporon cutaneum
D. Geotrichum candidum

A

A. Candida tropicalis

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21
Q

Dimorphic molds are found in infected tissue in which form?
A. Mold phase
B. Yeast phase
C. Encapsulated
D. Latent

A

B. Yeast phase

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22
Q

The mycelial form of which dimorphic mold produces thick-walled, rectangular, or barrel-shaped alternate arthroconidia?
A. Coccidioides immitis
B. Sporothrix schenckii
C. Histoplasma capsulatum
D. Blastomyces dermatitidis

A

A. Coccidioides immitis

23
Q

The yeast form of which dimorphic fungus appears as oval or elongated cigar shapes?
A. Coccidioides immitis
B. Sporothrix schenckii
C. Histoplasma capsulatum
D. Blastomyces dermatitidis

A

B. Sporothrix schenckii

24
Q

The mycelial form of H. capsulatum seen on agar resembles:
A. Sepedonium spp.
B. Penicillium spp.
C. Sporothrix spp.
D. Coccidioides spp.

A

A. Sepedonium spp.

25
Q

The yeast form of which dimorphic mold shows a large parent yeast cell surrounded by smaller budding yeast cells?
A. Paracoccidioides brasiliensis
B. Sporothrix schenckii
C. Coccidioides immitis
D. Histoplasma capsulatum

A

A. Paracoccidioides brasiliensis

26
Q

Which group of molds can be ruled out when septate hyphae are observed in a culture?
A. Dematiaceous
B. Mucorales (formerly Zygomycetes)
C. Dermatophytes
D. Dimorphic molds

A

B. Mucorales (formerly Zygomycetes)

27
Q

Tinea versicolor is a skin infection caused by:
A. Malassezia furfur
B. Trichophyton rubrum
C. Trichophyton schoenleinii
D. Microsporum gypseum

A

A. Malassezia furfur

28
Q

Which of the following structures is (are) invaded by the genus Trichophyton?
A. Hair
B. Nails
C. Skin
D. All of these options

A

D. All of these options

29
Q

An organism cultured from the skin produces colonies displaying a cherry-red color on Sabouraud dextrose agar after 3 to 4 weeks and teardrop-shaped microconidia along the sides of the hyphae. The most likely identification is:
A. Trichophyton rubrum
B. Trichophyton tonsurans
C. Trichophyton schoenleinii
D. Trichophyton violaceum

A

A. Trichophyton rubrum

30
Q

Which Microsporum species causes an epidemic form of tinea capitis in children?
A. Microsporum canis
B. Microsporum audouinii
C. Microsporum gypseum
D. All of these options

A

B. Microsporum audouinii

31
Q

Microscopic examination of a fungus cultured from a patient with athlete’s foot showed large, smooth-walled, club-shaped macroconidia appearing singly or in clusters of two to three from the tips of short conidiophores. The colonies did not produce microconidia. What is the most likely identification?
A. Trichophyton spp.
B. Alternaria spp.
C. Epidermophyton spp.
D. Microsporum spp.

A

C. Epidermophyton spp.

32
Q

Which Trichophyton species causes the favus type of tinea capitis seen in the Scandinavian countries and in the Appalachian region of the United States?
A. Trichophyton verrucosum
B. Trichophyton violaceum
C. Trichophyton tonsurans
D. Trichophyton schoenleinii

A

D. Trichophyton schoenleinii

33
Q

The hair baiting test is used to differentiate which two species of Trichophyton that produce red colonies on Sabouraud agar plates?
A. Trichophyton mentagrophytes and Trichophyton rubrum
B. Trichophyton tonsurans and Trichophyton schoenleinii
C. Trichophyton tonsurans and Trichophyton violaceum
D. Trichophyton verrucosum and Trichophyton rubrum

A

A. Trichophyton mentagrophytes and Trichophyton rubrum

34
Q

A mold that produces colonies with a dark brown, green-black, or black appearance of both the surface and reverse side is classified as a:
A. Dematiaceous mold
B. Dermatophyte
C. Hyaline mold
D. Dimorphic fungus

A

A. Dematiaceous mold

The dematiaceous molds are easily recognized and confirmed by observing dark-yellow or brown septate hyphae upon microscopic examination.

35
Q

A rapidly growing hyaline mold began as a white colony but soon developed a black “pepper” effect on the agar surface. The older colony produced a black matte, making it resemble a dematiaceous mold. What is the most likely identification?
A. Penicillium notatum
B. Aspergillus niger
C. Paecilomyces spp.
D. Scopulariopsis spp.

A

B. Aspergillus niger

36
Q

Which dematiaceous mold forms flask-shaped phialides, each with a flask-shaped collarette?
A. Phialophora spp.
B. Exophiala spp.
C. Wangiella spp.
D. All of these options

A

A. Phialophora spp.

37
Q

Which Aspergillus species, recovered from sputum or bronchial mucus, is the most common cause of pulmonary aspergillosis?
A. Aspergillus niger
B. Aspergillus flavus
C. Aspergillus fumigatus
D. All of these options

A

C. Aspergillus fumigatus

38
Q

A hyaline mold recovered from a patient with AIDS produced rose-colored colonies with lavender centers on sabouraud dextrose agar. Microscopic examination showed multiseptate macroconidia appearing as sickles or canoes. What is the most likely identification?
A. Fusarium spp.
B. Wangiella spp.
C. Exophiala spp.
D. Phialophora spp.

A

A. Fusarium spp.

39
Q

Material from a fungus-ball infection produced colonies with a green surface on Sabouraud agar in 5 days at 30 C. Microscopic examination showed club-shaped vesicles with sporulation only from the top half of the vesicle. This hyaline mold is most probably which Aspergillus spp.?
A. Aspergillus niger
B. Aspergillus fumigatus
C. Aspergillus flavus
D. Aspergillus terreus

A

B. Aspergillus fumigatus

A. fumigatus is the most common cause of aspergillosis. It is characterized by sporulation only from the upper half or two-thirds of the vesicle.

Colonies of *A. * are white with black pepper growth and produce phialides over the entire vesicle, forming the classic “radiate” head. A flavus colonies are yellow to yellow-green and produce phialides that cover the entire vesicle and point out in all directions. A. terreus produces brown colonies and phialides that also cover the entire vesicle.

40
Q

A rapidly growing nonseptate mold produced colonies with a gray surface resembling cotton candy that covered the entire plate. Microscopic examination revealed sporangiophores arising between, not opposite, the rhizoids and producing pear-shaped sporangia. What is the most likely identification?
A. *Lichtheimis (formerly Absidia)** spp.
B. Penicillium spp.
C. Rhizopus spp.
D. Aspergillus spp.

A

A. *Lichtheimis (formerly Absidia)** spp.

41
Q

An India ink test was performed on CSF from a male patient with HIV infection. Many encapsulated yeast cells were seen in the centrifuged sample. Further testing revealed a positive urease test and growth of brown colonies on niger seed agar. The diagnosis of meningitis was caused by which yeast?
A. Candida albicans
B. Cryptococcus neoformans
C. Cryptococcus laurentii
D. Candida tropicalis

A

B. Cryptococcus neoformans

42
Q

A bone marrow sample obtained from an immunocompromised patient revealed small intracellular cells using a Wright stain preparation. Growth on Sabouraud-dextrose agar plates of a mold phase at 25 C and a yeast phase at 37 C designates the organism as dimorphic. The mold phase produced thick, spherical tuberculated macroconidia. What is the most likely identification?
A. Histoplasma capsulatum
B. Sepedonium spp.
C. Sporothrix schenckii
D. Coccidioides immitis

A

A. Histoplasma capsulatum

Thermally dimorphic H. capsulatum produce microconidia and hyphae fragments at 37 C (yeast phase), whereas at 25 C (mold phase), the organism displays large, thick-walled, round macro conidia with knobby or knoblike projections. The yeast form is able to survive within circulating monocytes or tissue macrophages that can be demonstrated with Giemsa or Wright stain.

43
Q

A lung biopsy obtained from an immunocompromised patient showed many “cup-shaped” cysts (gray to black) in a foamy exudate (green background) using Gomori methenamine silver (GMS) stain. The organism cannot be cultured because it does not grow on routine culture media for molds. The patient was diagnosed with pneumonia resistant to antibiotic treatment. The most likely identification is:
A. *Pneumocystis jirovecii (previously Pneumocystis carinii)
B. Histoplasma capsulatum
C. Sporothrix schenckii
D. Scopulariopsis spp.

A

A. *Pneumocystis jirovecii (previously Pneumocystis carinii)

44
Q

Upon direct examination of a sputum specimen, several spherules that contained endospores were noted. Growth on Sabouraud-dextrose agar showed aerial mycelial elements. The septate hyphae produced barrel-shaped arthroconidia. What is the most likely identification?
A. Talaromyces (formerly Penicillium) marneffei
B. Scopulariopsis spp.
C. Cryptococcus neoformans
D. Coccidioides immitis

A

D. Coccidioides immitis

45
Q

A bone marrow sample obtained from an immunocompromised patient who tested positive for HIV. The organism grew rapidly at 3 days showing a mold form (at 25 C), displaying conidiophores with four to five terminal metulae with each having four to six phialides. The conidia at the end of the phialides were oval and in short chains. They appear as a fan or broom when viewing under 10x and 40x magnification. At 37C, the yeast form grew more slowly, showing conidia that formed hyphal elements breaking at the septa to produce oval arthroconidia. This thermodimorphic mold is most likely:
A. Paecilomyces spp.
B. Talaromyces (formerly Penicillium) marneffei
C. Rhizomucor spp.
D. Aspergillus fumigatus

A

B. Talaromyces (formerly Penicillium) marneffei

46
Q

What is the specimen of choice for the initial diagnosis of P. jirovecii (carinii) in an immunocompromised patient, such as someone with AIDS?
A. Induced sputum
B. Open-thorax lung biopsy
C. CSF
D. Urine

A

A. Induced sputum

47
Q

A transplant patient is suspected of having invasive aspergillosis on the basis of clinical and radiological findings. Which specimen is best for the initial identification of aspergillosis by soluble antigen testing?
A. Blood culture
B. Lung biopsy
C. Serum or urine
D. Sputum

A

C. Serum or urine

48
Q

What is the most common cause of mucormycosis infection in humans?
A. Penicillium spp.
B. Candida albicans
C. Scopulariopsis spp.
D. Rhizopus spp.

A

D. Rhizopus spp.

49
Q

** A thermally dimorphic fungus shows a filamentous mold form with tuberculate macroconidia at room temperature, and a yeast form above 35 C. Which organism best fits the description?**
A. Histoplasma capsulatum
B. Paracoccidioides brasiliensis
C. Candida albicans
D. Coccidioides immitis

A

A. Histoplasma capsulatum

50
Q

After a vacation to the southwestern United States, a midwesterner complained of flulike symptoms with fever, chills, nonproductive cough, and chest pain. Microscopic examination of sputum, cleared with KOH, revealed large, thick-walled spherules containing endospores. Upon culture, the mold phase showed septate hyphae and alternating barrel-shaped arthroconidia. Which organism is most likely the cause of this pneumonia?
A. Coocidioides immitis
B. Histoplasma capsulatum
C. Paracoccidioides brasiliensis
D. Talaromyces (formerly Penicillium) marneffei

A

A. Coocidioides immitis

C.immitis is a soil fungus and is endemic to the southwestern United States. Infection results from inhaling the arthroconidia, which form endospore-forming spherules and leads to infection within 1 to 3 weeks. No immunocompromised people usually do not require treatment and are immune to reinfection. However, immunodeficient persons may develop symptomatic pulmonary and multiorgan infections.

51
Q

Skin scrapings from a young male patient showed many yeast cells of oval and bottle-shapes with monopolar budding. The direct microscopic examination also showed hyphal elements with a “spaghetti and meatball” morphological appearance. The most likely identification of this yeast is?
A. Malassezia furfur
B. Candida glabrata
C. Candida albicans
D. Cryptococcus neoformans

A

A. Malassezia furfur

52
Q

Microscopically, Scopulariopsis spp. resemble Penicillium spp. Which of the following best differentiates the two?
A. Nonseptate hyphae and foot cells
B. Brush-like conidiophores and large echinulate conidia
C. No hyphae and no phialides
D. Growth at 45 C

A

B. Brush-like conidiophores and large echinulate conidia

Microscopically, Scopulaiopsis spp. resemble Penicillium spp. except for the following: Scopulariopsis spp. produce annellophores with flask-shaped annelides bearing large lemon-shaped, rough-walled conidia in chains; Penicillium spp. display brush-like conidiophores producing metulae with flask-shaped phialides, resulting in chains of small, smooth-walled conidia.

53
Q

A fast-growing (2-5 days) culture of fluffy white to blue-green colonies from a respiratory specimen obtained from an immunocompromised ICU patient showed septate hyphae with many conidiophores. The tips of the conidiophores expand into large dome-shaped vesicles with bottle-shaped phialides covering the upper half or two-thirds of its surface. Long chains of small conidia form a columnar mass on the surface. At the base of the conidiophore, a “foot cell” is seen attaching the conidiophore to the septate hyphae. The most likely organism is?
A. Penicillium spp.
B. Scopulariopsis spp.
C. Aspergillus fumigatus
D. Paecilomyces spp.

A

C. Aspergillus fumigatus

A “foot cell” is a characteristic of Aspergillus fumigatus. The presence of a foot cell, which is T- or L-shaped cell at the based of the conidiophore (It is not a separate cell), is characteristic and distinct for A. fumigatus which is thermotolerant, growing at temperatures up to 45C.

A3 - Microbiology - Harr (12 decks)

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