Mycology Flashcards
All of the following are examples of appropriate specimens for the recovery of fungi except:
D. Swab
For which clinical specimens is the KOH direct mount technique for examination of fungal elements used?
A. Skin
The India ink stain is used as a presumptive test for the presence of which organism?
B. Cryptococcus neoformans in CSF
Cutaneous disease involving skin, hair, and nails usually indicates an infection with a:
B. Dermatophyte
What is the first step to be performed in the identification of an unknown yeast isolate?
D. Germ tube test
An isolate produced a constriction that was interpreted as a positive germ tube, but Candida albicans was ruled out when confirmatory tests were performed. Which of the following fungi is the most likely identification?
A. Candida tropicalis
Cornmeal agar with Tween 80 is used to identify which characteristic of an unknown yeast isolate?
D. All of these options
Blastoconidia are the beginning of which structures?
C. Pseudohyphae
An isolate from CSF growing on cornmeal agar produces the following structures:
Which tests should be performed next?
A. Birdseed agar and urease
Which of the following yeasts is characteristically positive for germ tube production?
D. Candida albicans
Arthroconidia production is used to differentiate which two yeast isolates?
B. Trichosporon cutaneum and Cryptococcus
neoformans
The urease test, niger seed agar test, and the germ tube test are all used for the presumptive identification of:
B. Cryptococcus neoformans
Which of the following yeasts produces only blastoconidia on cornmeal Tween 80 agar?
D. Cryptococcus spp.
Ascospores are formed by which yeast isolate?
A. Saccharomyces cerevisiae
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?
B. Rhodotorula spp.
Which of the following yeast enzymes is detected using birdseed (niger seed) agar?
A. Phenol oxidase
Chlamydospore production is demonstrated by which Candida species?
C. C. albicans
Carbohydrate assimilation tests are used for the identification of yeast isolates by inoculating media:
A. Free of carbohydrates
Yeast recovered from the urine of a catheterized patient receiving chemotherapy for cancer gave the following results:
What further testing is necessary?
D. No further testing is needed for identification
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?
A. Candida tropicalis
Dimorphic molds are found in infected tissue in which form?
B. Yeast phase
The mycelial form of which dimorphic mold produces thick-walled, rectangular, or barrel-shaped alternate arthroconidia?
A. Coccidioides immitis
The yeast form of which dimorphic fungus appears as oval or elongated cigar shapes?
B. Sporothrix schenckii
The mycelial form of Histoplasma capsulatum seen on agar resembles:
A. Sepedonium spp.
Which group of molds can be ruled out when septate hyphae are observed in a culture?
B. Zygomycetes
The yeast form of which dimorphic mold shows a large parent yeast cell surrounded by smaller budding yeast cells?
A. Paracoccidioides brasiliensis
Tinea versicolor is a skin infection caused by:
A. Malassezia furfur
Which of the following structures is invaded by the genus Trichophyton?
D. All of these options
An organism cultured from the skin produces colonies displaying a cherry-red color on Sabouraud dextrose agar after 3–4 weeks and teardrop-shaped microconidia along the sides of the hyphae. The most likely identification is:
A. Trichophyton rubrum
Which Microsporum species causes an epidemic form of tinea capitis in children?
B. Microsporum audouinii
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?
C. Epidermophyton spp.
Which Trichophyton species causes the favus type of tinea capitis seen in the Scandinavian countries and in the Appalachian region of the United States?
D. T. schoenleinii
The Hair Baiting Test is used to differentiate which two species of Trichophyton that produce red colonies on Sabouraud agar plates?
A. T. mentagrophytes and T. rubrum
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
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?
B. Aspergillus niger
Which dematiaceous mold forms flask-shaped phialides, each with a flask-shaped collarette?
A. Phialophora spp.
Which Aspergillus species, recovered from sputum or bronchial mucus, is the most common cause of pulmonary aspergillosis?
C. A. fumigatus
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.
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.?
B. A. fumigatus
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. Absidia spp.
A bone marrow sample obtained from an immunocompromised patient revealed small intracellular cells using a Wright’s 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
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 that resisted antibiotic treatment. The most likely identification is?
A. Pneumocystis jirovecci (carinii)
Upon direct examination of a sputum specimen, several spherules were noted that contained endospores. Growth on Sabouraud–dextrose agar showed aerial mycelial elements. The septate hyphae produced barrel-shaped arthroconidia. What is the most likely identification?
D. Coccidioides immitis
A bone marrow specimen was 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 10× and 40×. At 37°C, the yeast form grew more slowly, showing conidia that formed hyphal elements breaking at the septa to produce oval arthroconidia. This thermo- dimorphic mold is most likely:
B. Penicillium marneffei
What is the specimen of choice for the initial diagnosis of Pneumocystis jirovecii (carinii) in an immunocompromised patient, such as someone with AIDS?
A. Induced sputum
An India ink test was performed on CSF from an HIV-infected male patient. 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?
B. Cryptococcus neoformans
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?
C. Serum or urine
What is the most common cause of mucormycosis infection in humans?
D. Rhizopus spp.
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 this description?
A. Histoplasma capsulatum
SITUATION: After a vacation to the Southwestern United States, a midwesterner complained of flulike symptoms with fever, chills, nonproductive cough, and chest pain. Microscopic exam 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. Coccidioides immitis
