Fungi: Candida albicans Dimorphism

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Questions and Answers

What is a characteristic required for a fungus to be a human pathogen?

Ability to digest plant tissues

Ability to grow at a high temperature, at or above 37°C (correct)

Ability to produce antibiotics

Ability to grow at low temperature

What is the estimated number of species of fungi?

200 000

150 000 (correct)

10 000

50 000

What is the role of fungi in nature?

Parasites of plants and animals

Saprophytes and catalysts in the carbon cycle (correct)

Decomposers and producers of antibiotics

Producers of toxins and pathogens

What is the term for the study of fungi?

Mycology Signup and view all the answers

What is a characteristic of eukaryotic fungi?

They have a nucleus Signup and view all the answers

What is an example of a drug produced by fungi?

Penicillin Signup and view all the answers

What is the term for fungi that can cause disease in humans?

Pathogenic fungi Signup and view all the answers

What is the estimated number of species of fungi that cause human diseases?

300 Signup and view all the answers

What is the typical arrangement of ascospores in an ascus?

In a linear order Signup and view all the answers

Which type of fungal spore is characterized by a club-shaped structure?

Basidiospore Signup and view all the answers

What is the function of the Oogonium in Oomycota?

Production of oospores Signup and view all the answers

What is the primary characteristic of opportunistic pathogens?

They take advantage of a host with a weakened immune system Signup and view all the answers

Which fungal classification system is no longer formally accepted as a taxon?

Deuteromycota Signup and view all the answers

What is the typical number of ascospores found in an ascus?

4-8 Signup and view all the answers

What is the term for the fusion of two sexually compatible hyphae or gametangia in Zygomycota?

Zygospore formation Signup and view all the answers

What is the term for the resting structures formed by certain fungi, characterized by thick walls?

Zygospores Signup and view all the answers

What is the primary characteristic of Candida albicans that distinguishes it from other fungi?

It can exist in both yeast and hyphal forms Signup and view all the answers

Which type of fungal reproduction involves the fusion of gametes?

Sexual reproduction Signup and view all the answers

What is the characteristic shape of yeast cells?

Spherical or oval Signup and view all the answers

What is the function of vegetative hyphae in a fungal mycelium?

To penetrate the media and absorb food Signup and view all the answers

What is the term for a chain of elongated budding cells that have failed to detach?

Pseudohyphae Signup and view all the answers

Which type of fungi is characterized by the formation of a network of filaments called hyphae?

Molds Signup and view all the answers

What is the term for the collection of hyphae that form a mat-like structure?

Mycelium Signup and view all the answers

What is the primary difference between a yeast and a mold?

Yeast cells are unicellular, while mold cells are multicellular Signup and view all the answers

What is the primary role of the capsule in Cryptococcus neoformans?

To protect the organism against certain stress conditions Signup and view all the answers

What is the optimal growth temperature range for most fungi?

20-35°C Signup and view all the answers

What is the primary mechanism of nutrition in fungi?

Secreting extracellular enzymes to digest polymeric materials Signup and view all the answers

What is the characteristic of dimorphic fungi?

Ability to exist in two forms depending on temperature Signup and view all the answers

What is the primary characteristic that distinguishes yeasts from molds?

Cellularity Signup and view all the answers

What is the term used to describe fungi that can grow in both aerobic and anaerobic environments?

Facultative anaerobes Signup and view all the answers

What is the primary role of fungi in the ecosystem?

Decomposers Signup and view all the answers

What is the term used to describe the ability of fungi to resist environmental stress conditions?

Resistance to environmental stress Signup and view all the answers

What is the primary function of fungal spores?

To allow fungi to be reproduced Signup and view all the answers

What is the main component of fungal cell walls?

α- and β- linked glucans Signup and view all the answers

What is the unique characteristic of the fungal cell membrane?

It includes sterol (ergosterol, zymosterol) Signup and view all the answers

What is the significance of spore morphology in fungi?

It is one of the most important features used for visual identification of fungi Signup and view all the answers

What is the primary function of ergosterol in fungal cells?

It is a specific target for antifungal agents Signup and view all the answers

What is the main difference between fungal cell walls and higher eukaryotic cell walls?

Fungal cell walls lack cholesterol Signup and view all the answers

What is the significance of the fungal cell wall in fungal reproduction?

It is involved in the formation of fungal spores Signup and view all the answers

What is the primary function of chitin in fungal cell walls?

It provides structural support to the cell wall Signup and view all the answers

Study Notes

Fungi: Cell Structure and Classification

Fungi are eukaryotic, and there are approximately 150,000 species, with only about 300 species causing human diseases.
They grow in nature as saprophytes on dead organic material and are important catalysts in the carbon cycle.
Fungi produce drugs, such as antibiotics (penicillin) and immunosuppressants (cyclosporin), and are involved in food microbiology and industrial microbiology.

Pathogenic Species

Plant pathogens
Animal pathogens
Human pathogens

Human Pathogens

To be a human pathogen, a fungus must: • Grow at a high temperature (at or above 37°C) • Reach the tissues it will parasitize by penetrating host tissue barriers or circumventing them through small airborne cells • Digest and absorb components of human tissues • Withstand the human immune system

Fungal Reproduction

Fungi reproduce sexually and/or asexually
Ascospores are usually arranged in a linear order in an ascus (sac) and can be 4-8 in number
Basidiospores are the sexual spores of Basidiomycota, formed in a club-shaped structure called a basidium
Zygospores are typical of Zygomycota, thick-walled spores formed when two sexually compatible hyphae or gametangia fuse together
Oospores are sexually produced spores of Oomycota, formed within a special female structure called an oogonium

Fungi Classification: Based on Sexual Reproduction

Ascomycota
Basidiomycota
Zygomycota
Deuteromycota (Fungi Imperfecti) - no longer formally accepted as a taxon, many of these fungi have yet to find a place in modern fungal classification

Opportunistic Pathogens

Microorganisms that do not cause disease in a healthy host
Take advantage of a host with a weakened immune system
Examples include some bacteria, viruses, fungi, and protozoa

Dimorphism of Candida albicans

DYC (daughter yeast cell)
GT (germ tube)
H (hyphae)
Ph (pseudohyphae)
YMC (yeast mother cell)

Fungi: Molds and Yeasts

Molds (filamentous fungi)
Yeasts • Unicellular, spherical, oval, 3-15 μm • Reproduce by budding • Pseudohyphae: a chain of elongated budding cells that have failed to detach (not true hyphae) • Form a bacteria-like colony (creamy)

Molds (Filamentous Fungi)

Multicellular, forming a network of filaments called hyphae
Septate-coenocytic (aseptate hyphae) - identification
Woolly (fuzzy) appearance in culture
The hyphae form together to produce a mat-like structure called a mycelium

Types of Hyphae

Vegetative hyphae: penetrate the media and absorb food
Aerial hyphae: directed above the surface of the media
Reproductive hyphae: aerial hyphae that carry different spores
Mycelium: a collection of hyphae

Hyphal Growth from Spore

Capsule

Cryptococcus neoformans
Complex polysaccharides
Main virulence factor
In the environment, the capsule plays a role in protecting the organism against some stress conditions
Disease caused by Cryptococcus species = Cryptococcosis

Growth Conditions

Optimum growth temperature: 20-35°C
Most fungi require a humidity level over 75% to grow
pH 5-7 (generally like acidic pH levels)
Aerobic or facultative anaerobic
Chemoheterotrophs
Growth rate: 1-2 days for yeasts, 4-21 days for molds

Nutrition and Physiology

Feed by secreting extracellular enzymes that digest polymeric materials (e.g., polysaccharides or proteins) into monomers that are assimilated as sources of carbon and energy
Decomposers (digest dead animal and plant materials)
Inorganic substances and salts
Fungi tend to be more resistant to environmental stress conditions than bacteria

Fungi Groups: On the Basis of Morphology

Yeasts: unicellular
Molds: multicellular (filamentous fungi)
Dimorphic fungi: ability to exist in two forms, e.g., yeast phase at 35-37°C and mold phase at 25°C

General Characteristics

Fungi lack chlorophyll and do not engage in photosynthesis (different from plants)
They produce spore structures (sexual-asexual spores)
Fungal spores are microscopic biological particles that allow fungi to be reproduced
Spore morphology is one of the most important features used for visual identification of fungi

Fungal Cell Wall

Complex and rigid cell wall composed of mannoproteins, chitins, α- and β-linked glucans (90%), lipids, protein (% 10)

Fungal Cell Membrane

Bilayered with inclusion of sterol (ergosterol, zymosterol), in contrast to the cholesterol typically found in higher eukaryotic membranes
ERGOSTEROL is a specific target for antifungal agents

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Description

This quiz covers the characteristics of Candida albicans, a fungus that can exist in different forms, including yeast and hyphae. It also covers the reproduction process and characteristics of yeasts.