MediaLab: Mycology: Yeasts and Dimorphic Pathogens

Which of the following dimorphic molds produces spherical or oval conidia, each supported by an individual conidiophore ("lollipop") as represented in the image on the right? Blastomyces dermatitidis Coccidioides immitis Histoplasma capsulatum Sporothrix schenckii

1

Illustrated in this photomicrograph of a lactophenol blue preparation of a urine sediment is a cluster of yeast cells that were presumptively identified as Cryptococcus species. What additional characteristics listed below may assist in confirming this identification? More than one answer is correct Rapid urease reaction Selective assimilation of dextrose and trehalose Production of ascospores on ascospore agar Strong phenoloxidase activity

1 and 4

Phialide:

A single, slender, tubular conidiophore.

Arthroconidia:

A spore that is formed from the hyphae by fragmentation. Microscopically, mature arthoconidia appear square, rectangular, or barrel-shaped with thick walls.

Chlamydoconidia:

Round, thick-walled spores. May be intercalary (within the hyphae) or terminal (on the end of the hyphae

Arrange in sequence the steps that should be taken to make a definitive identification of Cryptococcus neoformans

1. Observe mucoid appearing colony 2. Positive rapid urease reaction 3. Absence of pseudohyphae on cornmeal agar 4.Detect red-brown colonies on bird seed agar

All of the following observations are consistent with the laboratory identification of Cryptococcus neoformans EXCEPT: Colonies that appear mucoid on primary isolation culture medium Negative urease test Cornmeal agar morphology displaying spherical, irregular cells with no pseudohyphae Presence of capsular material Tan-brown pigment on bird seed agar

2

Although care should be taken when working with all fungus cultures in the laboratory, personnel are particularly prone to develop laboratory acquired infections from the inhalation of airborne species of which of the following fungi? Blastomyces dermatitidis Coccidioides immitis Sporothrix schenckii Histoplasma capsulatum

2

The colonies shown in this photograph were grown on Guizotia abyssinica (bird seed) agar at 30°C for 72 hours. What is the most likely identification? Cryptococcus laurentii Cryptococcus neoformans Candida parapsilosis Saccharomyces cerevisiae

2

The morphology of yeasts inoculated to cornmeal agar can be helpful in making a species identification. The field of view shown in the image on the right is most consistent with the identification of which of the following Candida species? C. kefyr (pseudotropicalis) C. (Torulopsis)glabrata C. parapsiolsis C. tropicalis

3

"Logs in a stream" blastoconidia

Candida kefyr

The presence of pseudohyphae and blastoconidia suggests the genus:

Candida

India ink stain

Cryptococcus neoformans

Coccidioides immitis and what animal go together?

Desert rodents

Which dimorphic fungus may produce black, yeast-like colonies after prolonged incubation at 37°C? Blastomyces dermatitidis Paracoccidioides brasiliensis Sporothrix schenckii Histoplasma capsulatum

3

Which of the following fungal infections is endemic in the southwestern United States' desert regions? Histoplasmosis Blastomycosis Coccidioidomycosis Sporotrichosis

3

Which of the following fungal species do not produce pseudohyphae on cornmeal agar? Candida albicans Candida guilliermondii Cryptococcus laurentii

3

The image on the right is a Gomori methenamine silver stain of a lung biopsy obtained from a patient with x-ray evidence of multi-focal pneumonitis. The infiltrating yeast cells are distinctly spherical, irregular in size, and separated by capsular material, appearing as a halo around each cell. What yeast will MOST likely be recovered in culture of this tissue, based on the microscopic morphology that is observed? Candida albicans Candida glabrata Cryptococcus neoformans

3

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: Thrush Tinea versicolor Chronic mucocutaneous candidiasis

2

The transmission of which of the following organisms is associated with the guano of bats? Blastomyces dermatitidis Histoplasma capsulatum Coccidioides immitis

2

Histoplasma capsulatum and what animal go together?

bats

The yeast forms of which of the following species of dimorphic fungi (represented in the image on the right) can be described as large yeast cells with multiple buds that are attached by narrow necks, giving the appearance of a "mariner's wheel"? Sporothrix schenkii Paracoccidioides brasiliensis Blastomyces dermatitidis

2

Which of the following is a phenotypic property of Saccharomyces yeast species that is helpful in establishing its species identification? Polysaccharide capsule Ascospore production Trehalose assimilation

2

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? Candida glabrata Candida albicans Cryptococcus species

2

Where is Histoplasma common?

caves Kentucky and other states in the lower Missouri and Mississippi river valleys

The formation of germ tubes when fetal bovine serum is inoculated with the yeast isolate leads to the presumptive identification of which of the following yeasts? Candida glabrata Candida parapsilosis Candida albicans Cryptococcus neoformans

3

Which Produce pseudohyphae on cornmeal agar and which don't: Candida albicans Cryptococcus laurentii Saccharomyces cerevisiae Candida guillirmondii Candida (Torulopsis) glabrata

do dont dont do dont

Blastomyces dermatitidis is commonly associated with close contact with what animal?

dogs

Colony morphology of Histoplasma capsulatum

gray-white and have a delicate cob-web appearance

Colony morphology of Coccidioides immitis

gray-white and have a delicate hair like consistency.

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? Chlamydospores Dense clusters of blastoconidia regularly along the pseudohyphae Blastoconidia with a "logs in stream" pattern "Spider" or "crossed matchstick" colonies

4

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? The urinary tract The lung Cardiac valves Intravenous catheter

4

Which of the following ingredients is added to culture media to enhance the recovery of the dimorphic fungi by preventing the overgrowth of more rapidly growing, saprophytic molds? Brain heart infusion base Chloramphenicol Thiamine Cycloheximide

4

Pseudohyphae:

A chain of elongated yeast cells resembling hyphae

Blastospore:

A fungal cell produced by budding.

Ascocarp:

A large saclike structure in which sexual spores are produced.

Conidia:

Asexual spores produced singly or in groups.

Chicagos disease

Blastomyces dermatiditis

What fungi looks like lollipops

Blastomyces dermatitidis

Dimorphic fungi that are considered pathogens include:

Blastomyces dermatitidis Histoplasma capsulatum Coccidioides immitis Paracoccidioides brasiliensis Sporothrix schenckii

Yeasts that produce blastospores only include:

Candida glabrata, Cryptococcus, Rhodotorula, and Saccharomyces.

What is a dimorphic fungi?

Growth as mold or Yeast

The spiked (echinulate) macroconidia is characteristic to what fungi?

Histoplasma capsulatum.

Macroconidia:

Large, multi-septate conidia that are club- or spindle-shaped.

Molds are generally identified using a combination of methods, including:

Microscopic morphologic features Morphologic features of colonies Growth rate

"mariner's wheel"

Paracoccidioides brasiliensis

Metulae:

Secondary branches

Microconidia:

Small, unicellular conidia that are round, elliptical, or pyriform (pear-shaped).

Asci:

Smaller sacs within an ascocarp containing four to eight ascospores.

Where is coccidiodes immitis commonly found?

Southwestern United States

Conidiophores:

Specialized hyphal strands that produce conidia

"cigar bodies"

Sporothrix schenckii

"rose growers' disease,"

Sporothrix schenckii

T/F Coccidioides immitis does not produce a yeast form in laboratory culture; rather, is identified in stained tissue sections by the production of varying sized spherules, ranging from 10 µm to over 100 µm in diameter

T

T/F The mold form of Coccidioides immitisis characterized by the production of arthroconidia that appear alternate staining because each cell is separated by an empty space. When mature, each arthroconidium is swollen centrally, giving a barrel appearance.

T

T/F 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

T

T/F Cryptococcus neoformans is an encapsulated yeast that can cause both pulmonary infections and meningitis, especially in immunocompromised hosts

T

T/F KOH is able to dissolve keratinaceous material; in thick discharges, to make yeast easier to detect

T

T/F The capsule of Cryptococcus will exclude the ink particles, so that a characteristic halo forms around the yeast cell.

T

The presence of true hyphae indicates the presence of:

Trichosporon, Blastoschizomyces capitus, or Geotrichum

Histoplasmosis can be transmitted through what?

guano of bats and birds, particularly chickens and blackbirds.

How is C. immitis transmitted?

inhalation of spores

Blastomyces dermatitidis characteristics

large, 10-15 µm in diameter, thick-walled yeast cell that characteristically produces a single bud attached by a broad base

Rhodotorula rubra color in culture:

orange-red pigmentation

Coccidioidomycosis is primarily a disease of what?

pulmonary

KOH preps are also useful for examining what type of samples?

skin, hair, nails, tissue, and respiratory specimens.

Histoplasmosis is a

systemic disease- mostly of the reticuloendothelial system

When grown on cornmeal agar, Geotrichum species are characterized by:

true hyphae that segment into rectangular arthroconidia. Arthrospores germinate from one corner, giving them a "hockey stick"

Candida albicans in culture:

yellow-white colonies from which "feet" extend out from the margins into the surrounding agar