Lab 9 - The Yeasts

What is mycology and what are mycoses?

Mycology is the study of fungi, and mycoses are diseases caused by fungi.

What are fungi?

Fungi are eukaryotic, chemoheterotrophic organisms that require organic compounds for both energy and carbon.

What are the two forms of fungi?

The two forms of fungi are yeasts and molds.

What is the difference between yeasts and molds?

Yeasts are unicellular and microscopic, while molds are multicellular, filamentous, and composed of hyphae.

What mode of nutrition do fungi use?

Fungi are chemoheterotrophs that obtain energy and carbon from organic compounds.

What carbon source do fungi use?

Fungi use organic compounds as both their energy source and carbon source.

Where do saprophytic fungi obtain their nutrients?

Saprophytic fungi obtain nutrients from decaying organic material.

Where do parasitic fungi obtain their nutrients?

Parasitic fungi obtain nutrients from living plants or animals.

What two modes of metabolism do yeasts exhibit?

Yeasts perform aerobic cellular respiration and fermentation.

What are organisms that can perform both respiration and fermentation called?

They are called facultative anaerobes.

What are yeasts?

Yeasts are unicellular, oval or spherical fungi.

How do yeasts reproduce?

Yeasts reproduce by budding.

What is a bud and a mother cell?

A bud is a small outgrowth that forms on the parent cell, and the mother cell is the original yeast cell from which the bud forms.

What are hyphae?

Hyphae are branching filamentous structures formed when buds remain attached.

What is the role of hyphae in pathogenesis?

Hyphae help fungi invade deeper into host tissues after colonizing the epithelium.

What are blastoconidia (blastospores)?

Blastoconidia are asexual spores that form in clusters along hyphae, often at branching points.

What are chlamydoconidia (chlamydospores)?

Chlamydoconidia are thick-walled survival spores that form at the tips of hyphae under certain conditions.

How can you identify blastospores vs. chlamydospores?

Blastospores appear as clustered budding cells along hyphae, while chlamydospores are larger, thick-walled, and located at hyphal tips.

What media can be used to grow yeast?

Yeasts can grow on Trypticase Soy Agar (TSA), Sabouraud Dextrose Agar (SDA), Mycosel agar, and Rice Extract agar.

How is SDA different from TSA?

SDA has a higher sugar concentration and lower pH, which promotes fungal growth and inhibits bacteria.

Is SDA selective or differential?

SDA is a selective medium.

What does SDA select for and inhibit?

SDA selects for fungi and inhibits bacterial growth.

Why is SDA (Sabouraud Dextrose Agar) selective?

Its low pH and high sugar concentration inhibit bacteria while favoring fungi.

What is Mycosel agar?

Mycosel agar is a selective medium used to isolate pathogenic fungi.

What does Mycosel agar select for?

It selects for pathogenic fungi.

What does Mycosel agar inhibit?

It inhibits bacteria (via chloramphenicol) and most saprophytic fungi (via cycloheximide).

Why is Mycosel agar selective?

It contains antibiotics that suppress bacteria and non-pathogenic fungi, allowing pathogenic fungi to grow.

What is Rice Extract agar used for?

Rice Extract agar stimulates formation of hyphae, blastoconidia, and chlamydoconidia in pathogenic yeasts like Candida albicans.

How do yeast colonies appear on solid media?

Yeast colonies appear similar to bacterial colonies due to their unicellular nature.

Which organisms grow on which media (general idea)?

TSA: grows bacteria and yeast; SDA: favors fungi, inhibits bacteria; Mycosel: selects pathogenic fungi; Rice Extract: promotes fungal structure formation (hyphae and spores).

Study before moving on to part 10

• Blastoconidia vs. Chlamydospores:

  • Blastospores are asexual spores formed by budding, often appearing as clusters along hyphae or from yeast cells.

  • Chlamydospores are thick-walled survival spores that form under stress, usually at the tips of hyphae.

• Rice Extract Agar:

  • It’s used to stimulate the formation of diagnostic fungal structures like hyphae, blastoconidia, and chlamydospores, particularly in Candida albicans.