Week 2 ,, Yeast

Where is Candida found?

Normal flora of the skin, mouth, vagina, and stool, along with the environment (leaves, flowers, water, and soil)

Fluconazole Prophylaxis

An anti-fungal medication that can cause patients to be more susceptible to fluconazole-resistant C. krusei and C. glabrata

Which is the most abundant and significant species of Candida?

C. albican

Disseminated

Having spread throughout an organ or body

What do C. albicans produce?

Secretory aspartyl proteases and phospholipase enzymes

Endogenous Infection of Candisiasis

From the overgrowth of the fungus inhabiting the normal flora

Exogenous Infection of Candisiasis

From catheters, prosthetic devices, or person-to-person transmission

Cornmeal Agar-Tween 80 (Dalmau Plate)

A nutrient poor medium used to identify yeast species (specifically C. albicans)

Sabouraud Dextrose Agar (SDA)

An acidic medium containing peptones and dextrose used for clinical yeast and mold isolation.

Germ Tube Test

A fast screening method used to presumptively identify C. albicans and C. dubliniensis from yeast colonies

Carbohydrate Assimilation Test

Measures a microorganism’s ability to use a specific sugar or carbon source for growth

Macroscopic Morphology of C. albicans

Cream to white, soft, smooth to wrinkled ,, grows at 42C and on cycloheximide

Macroscopic Morphology of C. glabrata

White, smaller, smooth, glistening ,, grows at 42C but fails on cycloheximide

Macroscopic Morphology of Rhodotorula Species

Rapid growing ,, smooth, glistening or dull, cream to pink, coral red, orange, or yellow ,, fails to grow on cycloheximide

Macroscopic Morphology of C. neoformans

Slower growing ,, soft, smooth, mucoid, cream to pink, or yellowish brown ,, grows at 37C but fails on cycloheximide

Microscopic Morphology (Cornmeal Agar) of C. albicans

Pseudohyphae and true hyphae with blastoconidia in grape-like clusters; terminal chlamydoconidia

Microscopic Morphology (Cornmeal Agar) of C. glabrata

Only small blasto-conidia ,, completely lacks hyphae and pseudohyphae

Microscopic Morphology (Cornmeal Agar) of Rhodotorula Species

Unicellular globose to elongate blastoconidia (may be encapsulated) ,, hyphae and pseudohyphae are absent/rudimentary

Microscopic Morphology (Cornmeal Agar) of C. neoformans

Round, budding yeast cells surround a polysaccharide capsule ,, no true hyphae and pseudohyphae is absent/rudimentary

Biochemical/Diagnostic Tests for C. albicans

Germ tube positive ,, API 20C

Biochemical/Diagnostic Tests for C. glabrata

Germ tube negative ,, API 20

Biochemical/Diagnostic Tests for Rhodotorula Species

Urease positive ,, fails to ferment carbohydrates

Biochemical/Diagnostic Tests for C. neoformans

Urease positive ,, phenoloxidase positive ,, india ink visible ,, latex aggulation positive

Which yeast species appears black/brown on bird seed/caffeic acid agar?

C. neoformans

Clinical Significance of C. albicans

Most common cause of opportunistic mycoses worldwide ,, highly pathogenic

Clinical Significance of C. glabrata

Decreased susceptibility to azoles ,, high risk in fluconazole prophylaxis ,, contributes to 21% pediatirc bloodstream mortality

Clinical Significance of Rhodotorula Species

Common environmental contaminant (soil, dairy, water) ,, rarely infects highly vulnerable hosts via catheters

Clinical Significance of C. neoformans

Causative agent of meningoencephalitis ,, contracted by inhalation (pigeon droppings/eucalyptus)

Identify the C. albican Structure

Yeast-like cells

Identify the C. albican Structure

Pseudohypha

Identify the C. albican Structure

Blastspore

Identify the C. albican Structure

Chlamydospore

C. glabrata on Cornmeal

Following a 72-hour incubation at 25C, only blastoconidia are observed

Rhodotorula spp.

Rarely isolated as causative agents of opportunistic mycoses in vulnerable hosts, such as patients with AIDS or acute leukemia

Identify the Infectious Yeast

Rhodotorula

Cryprococcus spp. Serotypes A and D

Included in var. neoformans ,, grow in pigeon droppings

Cryprococcus spp. Serotypes B and C

Included in var. gattii,, grow in eucalyptus tree wood

Identify the Infectious Yeast

C. neoforman

Which infectious yeast has a polysaccharide capsule?

C. neoformans

Which infectious yeast contains a phenol oxidase that produces melanin?

C. neoforman

What does the production of melanin do?

Prevents the formation of toxic hydroxyl radicals (oxidative stress)

Does Cryptococcus grow faster or slower than Candidia?

Slower

C. neoforman Microscopic Features

On cornmeal Tween 80 agar following a 72-hr incubation at 25C, produces round, budding yeast cells ,, capsule is best visible in india ink preparations

Identify the Infectious Yeast

C. neoformans

Antigen Latex Agglutination Test

A sensitive test system that can be used on serum and CSF ,, if present, the beads will clump