Mycology Review Flashcards
A culture is received in the lab with a comment to ‘rule out Malassezia furfur’. When processing the specimen what must be applied to the culture media to allow this organism to grow?
a. sugar solution
b. olive oil
c. a cover slip
d. immersion oil
b. olive oil
Malassezia furfur is a lipid-dependent organism. It will only grow on the media where olive oil has been applied.
Match each term with the correct description
Yeast
Mold
Aerial mycelium
Conidia
Hyaline
Ascus
Phialide
Dimorphic
a. Asexual reproductive spores
b. Fungus that has a yeast form and filamentous form
c. A large saclike structure in which sexual spores are produced
d. A single, slender, tubular conidiophore
e. Multicellular filamentous fungus
f. non-pigmented hyphae
g. Hyphae above the surface
h. Microscopic fungus which comprises a single, oval shaped cell
Yeast: Microscopic fungus which comprises a single, oval shaped cell
Mold: Multicellular filamentous fungus
Aerial mycelium: Hyphae above the surface
Conidia: Asexual reproductive spores
Hyaline: non-pigmented hyphae
Ascus: A large saclike structure in which sexual spores are produced
Phialide: A single, slender, tubular conidiophore
Dimorphic: Fungus that has a yeast form and filamentous form
Match each item on the left with it’s description on the right:
Saline wet mount
Lactophenol Cotton Blue
Potassium hydroxide (KOH)
Gram stain
India Ink
Calcofluor White
a. Used to stain and preserve fungal elements in culture isolates
b. Yeast will stain purple
c. Used to detect budding yeast in vaginal secretions
d. Flourochrome stain that stains chitin in the cell wall
e. Used to visualize capsule surrounding C. neoformans in CSF
f. Used to dissolve non-fungal material in skin, nail, and hair samples
Saline wet mount: Used to detect budding yeast in vaginal secretions
Lactophenol Cotton Blue: Used to stain and preserve fungal elements in culture isolates
Potassium hydroxide (KOH): Used to dissolve non-fungal material in skin, nail, and hair samples
Gram stain: Yeast will stain purple
India Ink: Used to visualize capsule surrounding C. neoformans in CSF
Calcofluor White: Flourochrome stain that stains chitin in the cell wall
A spinal fluid (CSF) specimen arrives in the lab with an order for fungal culture.
Select the best media to set up this specimen (choose all that applies):
- Sabouraud dextrose with brain-heart infusion agar (SABHI)
- Dermatophyte Test Medium (DTM)
- Brain-Heart Infusion Agar w/ blood (BHIB)
- Cornmeal Agar with Tween 80
- Sabouraud dextrose with brain-heart infusion agar (SABHI)
- Brain-Heart Infusion Agar w/ blood (BHIB)
Routine fungal cultures are incubated:
a. at 37C in a CO2 incubator
b. at 42C in a humid environment
c. at 4C
d. at 30C in a humid environment
d. at 30C in a humid environment
Match the fungal differential agar on the left with it’s use on the right:
Potato dextrose agar (PDA)
Bird seed agar
Cornmeal w/tween 80
a. C. neoformans will produce black to brown colonies due to the activity of phenol oxidase
b. used to enhance conidia development
c. used to differentiate Candida spp.
Potato dextrose agar (PDA): used to enhance conidia development
Bird seed agar: C. neoformans will produce black to brown colonies due to the activity of phenol oxidase
Cornmeal w/tween 80: used to differentiate Candida spp.
A germ tube test is performed on a yeast isolate from a throat culture on a 1y.o child. At 3 hours the test is read with the result seen in the image. How will you report this?
a. yeast isolated, NOT C. albicans
b. Candida glabrata isolated
c. albicans isolated
d. Cryptococcus neoformans isolated
c. albicans isolated
A germ tube test exhibited the structures shown in this image. What is the growth of the yeast cell called?
a. pseudohyphae
b.positive germ tube
c. hyphae
d. conidia
a. pseudohyphae
A 45-year old pigeon breeder, who is on immunosuppressive steroids complained to his physician of headache, dizziness, blurred vision and a stiff neck. Specimens of purulent CSF were sent to your microbiology laboratory. Gram stain of the CSF was reported as negative, however on brain heart infusion agar with blood, a white, mucoid yeast grew rapidly.
What test(s) will you use to identify this organism (choose all that applies)?
- Rapid Urea
- Phenyl oxidase production on bird seed agar
- Wood’s lamp fluorescence
- cornmeal agar morphology
- Rapid Urea
- Phenyl oxidase production on bird seed agar
Candida auris is a pathogen of public health concern because:
a. It is often multidrug resistant
b. It is difficult to identify in the clinical lab
c. It has caused outbreaks in healthcare settings
d. All of these are correct
d. All of these are correct
Which of the organisms listed below has the unique property of producing germ tubes when fetal bovine serum is lightly inoculated with the yeast isolate and incubated at 35 - 37° C for 2.5 - 3 hours?
a. Candida glabrata
b. Candida albicans
c. Cryptococcus species
d.Candida krusei
b. Candida albicans
Comment: Candida albicans often produces germ tubes when fetal bovine serum is lightly inoculated with the yeast isolate and incubated at 35 - 37° C for 2.5 - 3 hours.
Candida glabrata, Candida krusei, and Cryptococcus species do not produce germ tubes.
Cryptococcus species are characterized by the production of thick, polysaccharide capsules.
The growth of the yeast-like colonies shown in the upper image was obtained on blood agar from a skin culture only in the area overlaid by virgin olive oil. The lower image is a photomicrograph of a lactophenol blue mount made from a portion of the colony. The disease associated with this fungus is:
a. Thrush
b. Tinea versicolor
c. Chronic mucocutaneous candidiasis
d. Tinea corporis
b. Tinea versicolor
Comment: The yeast-like colonies seen growing on the blood agar surface are lipid-dependent and grow only where the olive oil has been applied. This is characteristic of the yeast-like organism, Malassezia furfur, which causes a superficial skin infection known as tinea versicolor.
None of the other yeast species listed in this exercise are lipid dependent and would have grown equally as well in areas removed from the olive oil droplets.
Thrush is a superficial infection of the mucous membranes of the oral cavity and/or vaginal canal caused by Candida albicans. C. albicans is also the underlying agent for chronic mucocutaneous candidiasis, a chronic erythematous, hyperkeratotic, crusting infection of the skin and mucous membranes, with particular prevalence in children with T cell dysfunction, or a variety of endocrine abnormalities.
Tinea corporis is a localized infection of the superficial skin caused by several species of filamentous dermatophytic fungi that do not have a yeast form.
Match each of the cornmeal agar morphologies listed in the drop-down box with the name of its corresponding yeast species on the right.
a. Candida kefyr
b. Geotrichum species
c. Rhodotorula
- “Hockey stick” arthroconidia
- Multilateral budding yeast cells
- “Logs in a stream” blastoconidia
a. Candida kefyr: “Logs in a stream” blastoconidia
b. Geotrichum species: “Hockey stick” arthroconidia
c. Rhodotorula: Multilateral budding yeast cells
Match each of the fungal species listed below with the appropriate category, indicating whether or not it has the capability of producing pseudohyphae on cornmeal agar.
a. Candida albicans
b. Cryptococcus laurentii
c. Saccharomyces cerevisiae
d. Candida guillirmondii
e. Candida (Torulopsis) glabrata
Produce pseudohyphae on cornmeal agar OR
Do not produce pseudohyphae on cornmeal agar
a. Candida albicans: Produce pseudohyphae on cornmeal agar
b. Cryptococcus laurentii: Do not produce pseudohyphae on cornmeal agar
c. Saccharomyces cerevisiae: Do not produce pseudohyphae on cornmeal agar
d. Candida guillirmondii: Produce pseudohyphae on cornmeal agar
e. Candida (Torulopsis) glabrata: Do not produce pseudohyphae on cornmeal agar
Comment: All Candida species, with the exception of Candida (Torulopsis) glabrata, produce pseudohyphae when grown on cornmeal agar; all Cryptococcus species do not.
Some environmental soil strains of Candida (Torulopsis) glabrata have been found to produce pseudohyphae. However, the strains that are encountered in clinical specimens do not produce pseudohyphae.
Although Saccharomyces cerevisiae may produce rudimentary pseudohyphae on cornmeal agar, the formation of budding blastoconidia is the more typical form seen in laboratory cultures and therefore, Saccharomyces cerevisiae should be placed in the category of not producing pseudohyphae on cornmeal agar.
A yeast identification system gave a biotype number for an unknown isolate that did not differentiate between Candida tropicalis and Candida parapsilosis. This isolate could be identified as C. parapsilosis in a cornmeal agar preparation if it produced which of the following?
a. Chlamydospores
b. Dense clusters of blastoconidia regularly along the pseudohyphae
c. Blastoconidia with a “logs in stream” pattern
d. “Spider” or “crossed matchstick” colonies
d. “Spider” or “crossed matchstick” colonies
Comment: Cornmeal agar morphology can be a valuable adjunct in separating two phenotypically, related species of Candida. Observing the patterns of growth and sporulation on cornmeal agar aids in the identification of an unknown yeast if the results derived from profile numbers generated by automated or kit systems do not provide sufficient information.
Candida parapsilosis produces a distinctive growth pattern on cornmeal agar with the unique formation of “spider” or “crossed matchstick” colonies as seen in the image on the right. Candida tropicalis, in contrast, produces unclustered pseudohyphae with blastoconidia irregularly spaced at points of septation.
The “logs in stream” arrangement of blastoconidia is characteristic of Candida kefyr (pseudotropicalis). Neither C. tropicalis nor C. parapsilosis produces chlamydospores.
Arrange in sequence the steps that should be taken to make an initial identification of Cryptococcus neoformans or Cryptococcus gattii.
- Positive rapid urease reaction
- Absence of pseudohyphae on cornmeal agar
- Observe mucoid appearing colony
- Detect red-brown colonies on bird seed agar
- Observe mucoid appearing colony
- Positive rapid urease reaction
- Absence of pseudohyphae on cornmeal agar
- Detect red-brown colonies on bird seed agar
Comment: Upon observing mucoid-appearing colonies on a primary isolation culture medium, perform a rapid urease test and set up a cornmeal agar preparation.
If the urease test is rapidly positive, observe the cornmeal agar morphology. If pseudohyphae are absent, and particularly if the yeast cells are spherical, irregular in size, and widely separated (presence of capsular material), inoculate the surface of a birdseed agar plate with a small portion of the unknown colony.
If a red-brown pigment is produced within 48-72 hours, a presumptive identification of Cryptococcus neoformans can be made. Recall that differentiating C. neoformans from C. gattii may only lead to definitive identification by using MALDI-TOF MS, nucleic acids, or with:
Growth on CGB (L-canavanine-glycine-bromothymol blue) agar, turning agar from green/yellow to a cobalt blue color in C. gattii.
The colonies illustrated in this photograph were recovered from a blood culture after 48-hour incubation at 30°C. What is the most likely source for the septicemia, based on the orange-pink colonies that are observed in culture?
a. The urinary tract
b. The lung
c. Cardiac valves
d. Intravenous catheter
d. Intravenous catheter
Comment: The correct answer is the intravenous catheter. The orange-pink yeast colonies seen in the image can be identified as Rhodotorula species. Fungemia has been the most common form of Rhodotorula infection, almost always associated with a catheter - either an indwelling intravenous catheter, an intraventricular shunt, or the catheter used in continuous peritoneal dialysis.
Illusrated in this photomicrograph of a lactophenol blue preparation of urine sediment is a cluster of yeast cells that were presumptively identified as Cryptococcus species. What additional characteristic(s) listed below may assist in confirming this identification?
a. Rapid urease reaction; strong phenoloxidase activity
b. Selective assimilation of dextrose and trehalose
c. Production of ascospores on ascospore agar
d. Weak phenoloxidase activity
a. Rapid urease reaction; strong phenoloxidase activity
Comment: Observed in this photomicrograph is a cluster of spherical, somewhat irregularly sized yeast cells that appear to be separated by capsular material. A few of the cells show a single bud connected by a delicate, hair-like attachment. These are microscopic characteristics suspicious for Cryptococcus species.
A rapid urease reaction would support this identification. The demonstration of strong phenoloxidase activity, either with a caffeic acid strip or with the use of birdseed agar, would confirm the identification of Cryptococcus neoformans or Cryptococcus gatti.
Most Cryptococcus species are saccharolytic and assimilate several carbohydrates in addition to trehalose.
The Cryptococci are not ascosporogenous yeasts; therefore, ascospores would never be observed.
The colonies shown in the upper image were obtained on blood agar from a sputum specimen after 10 days of incubation at 30°C. The lower image is a lactophenol blue mount made from a portion of the colony. What is the probable identification of the organism?
a. Coccidioides immitis
b. Blastomyces dermatitidis
c. Histoplasma capsulatum
d. Paracoccidioides brasiliensis
c. Histoplasma capsulatum
Comment: The colonies seen growing on the blood agar are gray-white and have a delicate cob-web appearance. This appearance plus the delayed growth is characteristic of one of the dimorphic fungi.
The lactophenol blue mount reveals delicate background hyphae (thus the cob-web appearance of the colonies) and the production of macroconidia with a conspicuous prickly surface, characteristic of Histoplasma capsulatum.
The mold form of Coccidioides immitis produces alternately staining arthroconidia and both Blastomyces dermatitidis and Paracoccidioides brasiliensis produce single, smooth microconidia, each borne on a single, thin conidiophore (“lollipops”).
The growth of the colonies shown in the upper image was obtained on blood agar from a sputum specimen after incubation at 30°C. The lower image is a lactophenol blue mount made from a portion of the colony. Based on the observed growth pattern and morphological features, what is a probable diagnosis?
a. Coccidioidomycosis
b. Blastomycosis
c. Histoplasmosis
d. Paracoccidiodomycosis
a. Coccidioidomycosis
Comment: The probable diagnosis is coccidioidomycosis. The colonies seen growing on the blood agar are gray-white and have a delicate hair-like consistency. The dark pigmentation indicates that some of the hemoglobin may have been absorbed from the culture medium. This appearance is characteristic of one of the dimorphic fungi. The growth rate may vary from 2-5 days.
The lactophenol blue mount in the lower image reveals thin hyphae that are breaking up into arthroconidia separated by empty cells, giving an alternately staining appearance. This is characteristic of the mold form of Coccidioides immitis.
The mold forms of Blastomyces dermatitidis and Paracoccidioides brasiliensis are characterized by the production of single, smooth microconidia, each borne on a single, thin conidiophore (“lollipops”).
The mold form of Histoplasma capsulatum is recognized by the production of large, echinulate macroconidia, appearing as a prickly surface.
The colonies shown in the upper image, obtained from a biopsy of an ulcerating skin lesion of the arm, are growing on agar slants of Sabouraud’s dextrose agar. The lower image is a lactophenol blue mount made from a portion of the colony. Which of the following organisms correspond to these findings?
a. Coccidioides immitis
b. Blastomyces dermatitidis
c. Histoplasma capsulatum
d. Sporothrix schenckii
d. Sporothrix schenckii
Comment: The colonies seen growing in the upper image have a gray-green, delicate, cottony consistency. The lactophenol blue mount reveals tiny, ovoid microconidia, arranged in a daisy-head pattern at the tip of a straight conidiophore. This appearance is characteristic of the mold form of Sporothrix schenckii. By moving the focus up and down in a microscopic preparation, delicate hair-like attachments may be observed for each conidium.
The mold form of Coccidioides immitis produces delicate hyphae that break up into arthroconidia separated by empty cells, giving an alternatively staining appearance.
The mold form of Blastomyces dermatitidis is characterized by the production of single, smooth microconidia, each borne on a single, thin conidiophore (“lollipops”).
The mold form of Histoplasma capsulatum is recognized by the production of large, echinulate macroconidia, appearing as a prickly surface.
The upper image illustrates a subculture of a mold colony suspected of being a dimorphic fungus inoculated to the surface of blood agar and incubated for three days at 37°C. Note that the colonies have a prickly appearance, suggesting an intermediate stage of conversion from mold to yeast. The lower image is a lactophenol blue mount of a portion of one of the prickly colonies. What is the probable identification of this fungus?
a. Coccidioides immitis
b. Blastomyces dermatitidis
c. Histoplasma capsulatum
d. Sporothrix schenckii
b. Blastomyces dermatitidis
Comment: The lactophenol blue mount (lower image) illustrates a short hyphal segment that is converting into spherical yeast forms. A few individual yeast forms are also observed. These yeast forms are relatively large and show a propensity toward budding with broad-based attachments. This is characteristic of the yeast conversion forms of Blastomyces dermatitidis.
Coccidioides immitis is extremely difficult to convert to the spherule form in laboratory cultures, and the attempt is virtually never made in clinical laboratories.
The yeast forms of Histoplasma capsulatum are tiny, uniform, budding cells, measuring around 2-3 µm in diameter.
The yeast forms of Sporothrix schenckii are also relatively small, ranging from 3-5 µm in dimension, with buds showing a distinctive elongated appearance, forming what is known as “cigar bodies”.
Match each of the names of the dimorphic fungal species shown with its mold form the drop-down box.
Histoplasma capsulatum
Coccidioides immitis
Blastomyces dermatitidis
Sporothrix schenckii
Histoplasma capsulatum: Image A
Coccidioides immitis: Image B
Blastomyces dermatitidis: Image C
Sporothrix schenckii: Image D
Comment: The spiked (echinulate) macroconidia seen in Image A is characteristic of the mold form of Histoplasma capsulatum.
The mold form of Coccidioides immitis (Image B) is characterized by the production of arthroconidia that appear with alternate staining because each cell is separated by a space. When mature, each arthroconidium is swollen centrally, giving a barrel appearance.
Blastomyces dermatitidis produces spherical or oval conidia, each supported by an individual conidiophore (“lollipop” as seen in Image C).
The mold form of Sporothrix schenckii is recognized by the production of tiny microconidia that are arranged around the tip of a delicate conidiophore as petals on a daisy flower (Image D).
The images below are lactophenol blue mounts of the yeast forms of various dimorphic fungi. Which of the images is consistent with an identification of Sporothrix schenckii?
This image illustrates a lactophenol blue mount of a mold recovered after 7 days of incubation of brain heart infusion broth. The large macroconidia suggest the mold form of Histoplasma capsulatum. However, there is the possibility that this mold represents its saprophytic counterpart. Which of the following is the saprophytic counterpart to H. capsulatum?
a. Chrysosporium species
b. Malbranchia species
c. Sepedonium species
d. Coccidioides immitis
c. Sepedonium species
Comment: Each of the dimorphic fungi, except Sporothrix schenckii, has a saprophytic counterpart with similar, look-alike microscopic features.
Sepedonium species share the production of large, spherical macroconidia with the mold form of Histoplasma capsulatum. When mature, the macroconidia may have a prickly surface, as seen in this image.
Chrysosporium species share the production of small, smooth, oval microconidia with the mold form of Blastomyces dermatitidis. The microconidia are each supported by a delicate conidiophore (“lollipop”).
Malbranchia species simulate the mold form of Coccidioides immitis by producing alternate staining arthroconidia. (C. immitis is not a saprophytic mold.)
A bulldozer operator became ill while working on a new highway in the San Joaquin Valley. She came to the urgent care complaining of chest pain, anorexia, headache, and myalgia with fever. Chest X-ray showed pneumonic infiltrate and a single, well-defined nodule in the left lower lobe.
The laboratory received a respiratory specimen for fungal culture. No fungus was seen in direct examination of the sputum. At day 3 the culture plate incubated at 30 degrees Celsius produced moist, grayish growth, and white aerial mycelia began to develop. A lactophenol cotton blue mount of the organism is seen below:
What is the most likely identification of this fungus?
a. Aspergillus fumigatus
b. Blastomyces dermatitidis
c. Coccidiodes immitis
d. Histoplasma capsulatum
c. Coccidiodes immitis
A 44-year-old gardener pricked herself with a rose thorn. 2-weeks later she noticed ulcers on her skin where she had been pricked. A fungal culture was submitted and the lab noted a small yeast form at 35 degrees Celsius and a mold at room temperature. A lacto phenol cotton blue mount of the mold growth exhibited the following:
This disease is:
a. Blastomycosis
b. Chromomycosis
c. Mycetoma
d. Sporotrichosis
d. Sporotrichosis
Dermatophyte Test Medium (DTM) was received in the lab from a Dermatology clinic. What initial information can you report?
a. Yeast isolated
b. No dermatophytes isolated
c. Aspergillus niger isolated
d. Dermatophyte isolated
d. Dermatophyte isolated
A 24-year-old Vietnamese student was seen at a clinic in Houston. His chief complaints were weight loss and fever. A complete blood count confirmed he was suffering from anemia as well. Multiple skin lesions were present on his arms, some of them draining pus.
Gram stain of the pus revealed what appeared to be yeastlike cells. A culture of the pus grew a green mold at 22 degrees Celsius, which produced a red soluble pigment.
A lactophenol cotton blue wet mount of this organism is seen below:
The most likely causative agent in this case is:
a. Aspergillus fumigatus
b. Fusarium spp
c. Talaromyces marneffei
d. Trichoderma spp
c. Talaromyces marneffei
