Parasitology & Mycology: Week 14 - Yeasts

What types of test results does C. neoformans produce?

*Bird Seed Agar/Caffeic Acid test (+)* Germ tube test (-) *Urease (+)*

What test results do C. albidus produce?

*Urease (+)* *Bird Seed Agar/Caffeic Acid test (-)*

What population is most affect by Cryptococcus infection?

Immunocompromised hosts; worldwide 7-10% of AIDS patients are affected. AIDS-associated cryptococcosis accounts for 50% of all cryptococcal infections

What is a germ tube?

A tubular out-pouching that occurs in some yeast cells *without constriction* at its base. Usually half the width and 3-4 times the length of the cells from which they form.

What species of Candida is an emerging pathogen which antibiotic resistance?

Candida auris

What species of Candida accounts for approximately 20% of urinary tract yeast isolates?

Candida glabrata

Candida tropicalis

Candida species which produces infection in *immunocompromised* patients and can be found as *normal flora* in humans.

Candida glabrata

Candida species which produces infections in the bloodstream (*fungemia*) and *urogenital tract*. Can also be normal flora.

Describe the macroscopic morphology of C. tropicalis.

Colonies are cream-colored and may show wrinkling at the edge of the colonies on blood agar.

Describe the macroscopic morphology of C. glabrata.

Cream colored colonies which are small and yeast-like

Describe the macroscopic morphology of C. albidus.

Cream-colored colonies

Describe the colony morphology of C. albicans.

Cream-colored colonies which are pasty and smooth. On *blood agar* "feet" may form at the colonies' edges

What is the most common clinical manifestation of cryptococcosis?

Dissemination to the brain/meninges (meningoencephalitis)

Describe the macroscopic morphology of C. neoformans.

Flat or slightly heaped, shiny, most and may be mucoid.

What are some tests which can confirm the identify of C. albicans?

Germ-tube test (+) Urease (-)

What germ-tube and urease test results does C. glabrata produce?

Germ-tube test (-) Urease (-)

What test results does C. tropicalis produce?

Germ-tube test (-) Urease (-)

Cryptococcus neoformans

Rapidly-growing, encapsulated round yeast (5-10 µm) with a predilection for the respiratory and nervous systems of humans/animals.

What is the germ tube test?

Procedure used to identify C. albicans. Performed by placing yeast colony into 0.5 cc of *rabbit plasma*, incubation at 35 C and then examination under 10x and 40x.

Describe the microscopic morphology of C. glabrata

Produces *oval* yeast cells, with single, terminal budding (i.e., one bud per cell). *No pseudohyphae* are present.

Describe the macroscopic morphology of Rhodotorula sp.

Produces *pink or coral* colonies which are soft, moist and may be mucoid.

Describe the microscopic morphology of C. tropicalis.

Produces pseudohyphae (w/some true hyphae), blastoconidia singly or in small chains along the pseudohyphae; *teardrop-shaped chlamydospores* may be present.

Cryptococcus albidus

Rapid-growing Cryptococcus which may be normal flora

Rhodotorula sp

Rapid-growing yeast and common contaminate, produces severe infections in *immunocompromised* patients with central venous catheters

Describe the microscopic appearance of C. albidus.

Round blastoconidia

Describe the microscopic morphology of Rhodotorula sp.

Round to oval budding cells w/*rare pseudohyphae*; faint capsule may form

Describe the microscopic morphology of C. albicans.

Round to oval cells (about 4-8 µm), produces pseudohyphae which clusters of *blastoconidia* forming at the *septae*. May also produce *chlamydospores*, usually terminal.

Where can Candida albicans cause infection?

Sterile body sites (e.g., blood, urine, CSF)

What is the caffeic acid test?

Tests for production of *phenoloxidase*; filter paper disks impregnated with caffeic acid are smeared w/small inoculum of yeast colony. Development of *dark-brown pigment* (melanin)What indicates positive result.

Describe the microscopic appearance of C. neoformans.

Yeast cells are round, dark-walled and budding; *does not produce hyphae/pseudohyphae*, *encapsulated*

Candida albicans

Yeast found as normal microbiota of the mouth, skin, vaginal and gastrointestinal tracts. *Most common cause of candidiasis*.