Mycology Chapter 62 Yeasts

Germ tube test identifies

75% of yeasts.

Name 6 yeast identification systems

API-20C AUX Yeast system Uni-yeast Tek system Microscan Yeast ID panel Vitek biochemical cards CHROMagar RapID Yeast plus system

Cryptococcus neoformans can minfests as what type of infection?

Acute, subacute or chronic

How are infections acquired from Cryptococcus?

Aerosolization.

What is phenoloxidase?

An ezyme in Cryptococcus neoformans that produces melanin, which is used as a virulence factor.

Cryptococcus neoformans macroscopic morphology

Appears in 1-5 days as a smooth, white to tan colony and are mucoid and creamy.

Saprochaete species belongs to the

Ascomycetous yeasts

What kind of yeast is Cryptococcus spp?

Basidiomycetous yeast.

Malassezia spp

Basidiomycota Skin of humans and animals Superficial skin disease, pulmonary and bloodstream infections Many are lipophilic

Candida microscopic characteristics

Budding yeast cells (blastoconidia) and/or pseudohyphae showing regular points of constriction, resembling links of sausages.. STRONGLY gram positive.

Candida albicans complex

C. albicans, C. dubliniensis, C. africana

CHROMagar is used for

Candida species

The PNA FISH kit is used for identification of

Candida species.

What yeast is the most common opportunistic that causes fungal infection?

Candida spp.

What tests provides definitive identification and additional tests are unnecessary?

Carbohydrate utilization tests

Where may Cryptococcus neoformans migrate to in immunocompromised patients?

Central nervous system.

What is the telemorphic form of Cryptococcus?

Filobasidiella neoformans

Two morphology characteristic of yeasts

Germ tube Pseudohyphae

Identification of Malassezia

Growth on overlaid agar(olive oil) and presence of bowling pin or pop bottle morphologic features.

Trichosporon Microscopic morphology

Hyaline hyphae Numerous arthroconidia Few blastoconidia

Rapid trehalose test

Identification of C. glabrata

What does cornmeal agar determine?

If the yeast produces blastoconidia, arthroconidia, pseudohyphae, true hyphae, and chlamydoconidia

How is melanin used as a virulence factor of Cryptococcus neoformans?

Makes the organism resistant to leukocyte attack.

What do yeasts look like macroscopically?

Moist, creamy colonies

Geotrichum candidum

Normal flora Opportunistic pathogen Respiratory infections

Malassezia microscopic morphology

Oval cells with monopolar budding with a cell wall that has a septum at the site of the bud scar. *Spaghetti and meatballs.

Disseminated cryptococcosis

Painless papular skin lesions Endocarditis Hepatitis Renal infection

Niger seed agar detects

Phenoloxidase

Cryptococcus neoformans and Cryptococcus deneoformans is found in

Pigeon or other bird excreta.

Ustilago species

Plant pathogen that causes significant damage to crops. Associated with disseminated infection

What are a few virulence factors of Cryptococcus neoformans?

Polysaccharide capsule Lipases, proteases, and urease Melanin

Identification of Trichosporon includes

Presence of rectangular arthroconidia with round ends and septate hyaline hyphae. Urease positive.

The production of urease caused by Cryptococcus neoformans results in

Promotes the accumulation of immature dendritic cells, making phagocytosis ineffective.

How does the polysaccharide capsule help Cryptococcus neoformans?

Protects yeast from environmental stress and is not recognized by phagocytes.

Which yeast is considered achlorophyllous algae but included in yeastlike organisms?

Prototheca species

What is the initial presentation of Cryptococcus neoformans?

Pulmonary infection.

Candida macroscopic characteristics

Smooth, creamy white colonies They can appear starlike or possess feet like projections

Cryptococcus microscopic morphology

Spherical, single or multiple budding, thick walled yeasts with a capsule. Has extreme variation in size.

Where is saprochaete species found?

Summers are hot and dry with warm wet winters May inhabit the skin, respiratory and GI tract

Trichosporon causes

Trichosporonosis and white piedra

Cryptococcus gattii

Tropical/sub tropical EUCALYPTUS TREES (Gum trees) Infections in immunocompromised and competent

What is a germ tube?

Tubular outpouch of cell wall, does not have constriction at its base. *True hyphae formation.

What is a bud scar?

When the daughter cell eventually detaches from the mother cell, and a residual defect occurs at the budding site.

What is candidiasis?

Yeast infection caused by Candida albicans

Saccharomyces cerevisiae can be used to prevent and treat

antibiotic-associated diarrhea including C. difficile

Yeasts reproduce sexually by

ascospores or basidiospores

Saccharomyces cerevisiae is commonly used in

baking products and probiotics.

Candida albicans produces BOTH

beta-galactose-aminidase and 1-proline aminopeptidase.

Yeasts reproduce asexually by

budding (blastoconidia)

If the yeast macroscopic is mucoid or shiny,

capsule may be present

What is pseudohyphae?

chain of yeast formed when buds remain attached in a row, has cell wall constriction *sausage

C. albicans complex can be identified by the production of

germ tubes or chlamydoconidia.

A quantitive test used for C. neoformans is the

leteral flow immunoassay that identifies the antigen

Non-albicans candida infections are in patients who are

older, have malignancies, in oncology care setting and neonatal intestive care unit.

Presumptive identification of C. neoformans is based on

production of urease.

Cryptococcus neoformans grows on

routine fungal media without cycloheximide.

Malassezia specimens

skin scrapings.

Final ID of C. neoformans is based on

substrate utilization and pigment production on niger seed agar.

Malassezia furfur causes

tinea versicolor (skin lesions)

Yeasts are

unicellular eukaryotes

Trichosporon Macroscopic morphology

Cream, heaped, and dry to moist wrinkled colonies.

Which cryptococcus is most commonly isolated in Europle?

Cryptococcus deneoformans

Which cryptococcus is most commonly isolated in immunocompromised patients worldwide?

Cryptococcus neoformans

Why is malassezia infrequently cultured?

Cultuivation requires agar overlaid with olive oil (Fatty acids)

Why is the india ink stain not always used for Cryptococcus species?

Delineates the large capsule

How do you prevent the paradox of where the patient's immune system improves, and then shortly after an exaggerated response known as immune reconstitution inflammatory syndrome (IRIS)?

Diagnose cryptococcal menigitis early and adminster antifungals to reduce the fungal burden in conjuction with immune modulators to block the influx of macrophages to the CNS, preventing IRIS.

Rhodotorula species is found in

Environment, food, beverages, skin, freshwater including bathtubs, showers and pools

Sporobolomyces species

Environmental organisms that can be found in aquatic habitats (Freshwater lakes) and birds, plants, mammals.