Fungi Flashcards by Anonymous Female

What fungal enzymes degrade plant cell walls?

Pectinases, Cellulases and Liginases

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Give a use for Neurospora crassa

Model for fungal systems in genetics

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Fungal Biological Control Agents

Verticillium lecanii (kills whitefly and thrips)

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Describe Candida albicans (yeast)

Causes candidiasis or thrush (regular thrush in immunocompetent patients)
Dimorphic yeast
Filamentous form when invasive
Hyphae invade tissue
Human pathogen
Mostly unicellular organism
Causes systemic infection in immunocompromised patients (organ failure, blood poisoning)

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Fungi are the primary cause of disease in…

plants

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Aspergillus fumigatus (fungus)

Thermophile
Small light spores that germinate mycelium in lungs called aspergilloma
Grows in green filamentous form
600 species
Causes 80% of aspergillosis disease
Hyphae invade and excretes enzymes to kill cells and absorb nutrients.
Necrosis can be fatal

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Dermatophytes and Trichophyta

Do not cause disease
Non-invasive, superficial infections on healthy host
Trichophyta is a ring worm causing athletes foot
Over 1million nail infections in UK (keratin lover)

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What key drugs do we use to control fungal infections?

Azoles and polyenes (ergosterol dependent)

5 fluorocytosine (fungistatic)

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What are the azoles?

What do they do?

Ketoconazole
Fluconazole

Prevent demethylation of sterol to ergosterol (component in membrane specific to fungi)

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Give an example of a polyene and what does it do?

Amphotericin B

Makes fungal membranes leaky, the cytosol leaks out.

High affinity to ergosterol (component in membrane specific to fungi) but is still toxic to body cells, can cause liver and kidney failure. So last resort.

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What does 5 fluorocytosine do?

Fungistatic (slows and stops growth but doesn’t kill fungus)

Replaces cytosine in RNA synthesis so mRNA becomes non-functional so fungus can’t make proteins to grow.

Fungal cells absorb fluorocytosine more readily than animal cells

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Define mycoses

Disease caused by fungi

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Name a mycotoxin, what produces it, and why.

The fungus Aspergillus flavus releases the mycotoxin aflatoxin to protect its food source.

Nuts are screened for this, can cause liver failure.

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What is a true pathogen

Affects the healthy host
Adapted to low oxygen tension (like in body)
Adapted to high temperature (like in body)
Approximately 10 species known to cause systemic infection

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Four genera that are prominent true pathogens

What do they have in common?

Histoplasma
Blastomyces
Coccidioides
Paracoccidioides

All display thermal dimorphism (fungal to yeast) and are usually asymptomatic in host.
Not obligate parasites, not major health problem, they can live as saprophytes.

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Define obligate parasite

Obligated to (must) infect host to complete their life cycle and reproduce

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Define saprophytes

Organism that obtains nutrients from dead organic matter

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What is thermal dimorphism?

At < 30 degrees, filamentous form, saprophytic.

At ~ 30 degrees (host body temperature), hyphal form reproduces via endospore production. Yeast growth, derives nutrients from host. Can become systemic.

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True or False:

Coccidioidomycosis is asymptomatic in 60% of cases

True

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True or False:

Coccidioidomycosis is asymptomatic in 40% of cases

False

Coccidioidomycosis is asymptomatic in 60% of cases

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True or False:

Coccidioidomycosis causes fever in 40% of cases

True

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True or False:

Coccidioidomycosis causes fever in 60% of cases

False

Coccidioidomycosis causes fever in 40% of cases

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True or False:

Coccidioidomycosis’ saprophytic form produces arthrospores (infectious agent)

True

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True or False:

Coccidioidomycosis causes growth in the lungs (fungoma) in 60% of cases

False

Coccidioidomycosis causes growth in the lungs (fungoma) in <0.5% of cases

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True or False: | Histoplasmosis is an example of a true pathogen disease

True | Caused by Histoplasma capsulatum

What does the filamentous form of histoplasmosis look like? At what temperature is it in this form?

Brown colony <35 degrees

What does the yeast form of histoplasmosis look like? At what temperature is it in this form?

White waxy yeast At 37 degrees (body temperature)

What is the infection cycle for histoplasmosis?

Bird droppings -> spores inhaled -> infects lung locally (can cause pneumonia) In lung, grows as yeast, then forms endospores and cycle continues

True or false: | In most cases of histoplasmosis phagocytes are able to limit and remove the infection

True | <50 deaths per year

True or false: | Most cases of histoplasmosis affects the lungs, heart and liver tissues and become fatal

False In most cases of histoplasmosis, infection stays local to the lung and phagocytes are able to limit and remove the infection <50 deaths per year

What pathogen causes histoplasmosis?

Histoplasma capsulatum

Coccidioidomycosis is caused by what pathogen?

Coccidioides immitis

True or False: | Arthrospores in Coccidioidomycosis grow as sporangia and release spores in the lung

True

When might Coccidioidomycosis lead to (potentially fatal) meningitis and rashes?

If the host is immunocompromised

True or false: | Coccidioidomycosis is a fungal infection which is usually cleared by the immune system

True

Define opportunistic pathogen?

Pathogens that target immunocompromised hosts

Give two examples of people who might be immunocompromised

People with HIV | People with transplants

True or False: | Opportunistic pathogens show no specific adaptation to the host

True | They are still hardy to the host environment

True or False: | Opportunistic pathogens show specific adaptation to the host

False | Opportunistic pathogens show no specific adaptation to the host. They are still hardy to the host environment though.

True or False: | Opportunistic pathogens infections can be superficial

True

True or False: | Opportunistic pathogens infections can be benign

True

True or False: | Opportunistic pathogens can lead to chronic systemic infection

True | Prognosis in this case is very poor, mortality rate is high

True or False: | Opportunistic pathogens cannot lead to chronic systemic infection

False Opportunistic pathogens can lead to chronic systemic infection, and prognosis in this case is very poor, mortality rate is high

What pathogen causes candidiasis / thrush?

Candida albicans

True or False: | 20% of us carry Candida albicans as a commensal organism

True

True or False: | 65% of us carry Candida albicans as a commensal organism

False | 20% of us carry Candida albicans as a commensal organism

True or False: | 20% of us carry Aspergillus fumigatus as a commensal organism

False | 20% of us carry Candida albicans as a commensal organism, not Aspergillus fumigatus

True or False: | In immunocompetent hosts infection from Candida albicans is limited to regular thrush (local infection).

True

True or False: | In immunocompetent hosts infection from Candida albicans can cause organ failure

False | In immunocompetent hosts infection from Candida albicans is limited to regular thrush (local infection).

True or False: | In immunocompromised hosts infection from Candida albicans is limited to regular thrush (local infection).

False | In immunocompromised hosts infection from Candida albicans can spread and cause organ failure and blood poisoning.

True or False: | In immunocompromised hosts infection from Candida albicans can spread and cause organ failure and blood poisoning.

True

What is the most common fungal pathogen to cause death, and is the fourth biggest killer in tertiary care hospitals?

Candida albicans (Thrush / candidiasis)

True or False: | Candida albicans is a dimorphic yeast

True

What is different about Candida albicans to other dimorphic yeasts?

It's usual form is the yeast form, its invasive form is the filamentous form, triggered at high temperatures.

What fungus causes >80% of Aspergillosis cases?

Aspergillus fumigatus

What does the filamentous form of Aspergillus fumigatus look like?

Green filamentous form

Where do the spores of Aspergillus fumigatus germinate and what do they produce?

Spores germinate in the lungs | They produce a mycelium in the lung, called an aspergilloma

True or False: | Aspergillus fumigatus uses hyphae and enzymes to aggressively break down cells and cause necrosis

True

What is the name for fungi that cause disease in plants?

Phytopathogenic fungi

Why are phytopathogenic fungi a major concern?

Food security

What are the most prominent examples of pathogens of immature tissue (plants)?

Pythium and Phytothphora | these are protists that used to be classed as fungi

True or False: | Pythium and Phytothphora are protists that used to be classified as fungi

True After analysis with modern molecular techniques they were found to be more closely related to algae and were reclassified as protists.

True or False: | Pythium and Phytothphora are fungi that used to be classified as protists

False Originally classified as fungi, but after analysis with modern molecular techniques they were found to be more closely related to algae and were reclassified as protists.

True or False: | Pathogens of immature tissue have no host specific adaptations and therefore have a broad host range.

True

True or False: | Pathogens of immature tissue are mainly soil borne infections

True

How do Pythium and Phytothphora infect plants?

They aggressively invade the new cells at root tips with weaker cell walls. Infection causes necrosis of root tip and stunts growth

How did Pythium and Phytothphora make history?

They caused the Irish potato famine in the 1840s

Why are Pythium and Phytothphora known as damping-off diseases?

They are associated with water-logged soils.

True or False: | Pathogens of mature tissue show a high degree of host specificity

True

True or False: | Pathogens of immature tissue show a high degree of host specificity

False: | Pathogens of immature tissue have no host specific adaptations and therefore have a broad host range.

True or False: | Pathogens of mature tissue have no host specificity

False: | Pathogens of mature tissue show a high degree of host specificity

What are necrotrophic pathogens

Necrotrophic pathogens excrete toxins & enzymes digest the cell wall. Kills the host and extracts nutrient from the dead cells. (Plant knows it is infected and mounts a resistance response)

Give an example of a necrotrophic pathogen

Amillaria mellea | honey fungus

``` True or False: Amillaria mellea (honey fungus) uses rhizomorphs to attack the plant and target the phloem tissue carrying sugars through the plant ```

True

``` True or False: Aspergillus fumigatus (honey fungus) uses rhizomorphs to attack the plant and target the phloem tissue carrying sugars through the plant ```

False Amillaria mellea is the honey fungus which uses rhizomorphs to attack the plant and target the phloem tissue carrying sugars through the plant (not Aspergillus fumigatus)

What are the rhizomorphs in the Amillaria mellea?

The rhizomorphs are macrostructures composed of collections of filaments or hyphal cells.

What enzymes do the rhizomorphs use to break down/kill the cells to transport the nutrients back to Amillaria mellea?

Ligninases, pectinases and cellulases

Fill in the gap: | The 'graminis' is Ersyphie graminis and Puccina graminis refers to how they infect ______

Wheat

True or False: | Biotrophic pathogens infect immature tissue

False | They infect mature tissue

True or False: | Biotrophic pathogens infect mature tissue

True

True or False: | Biotrophic pathogens give the appearance of rust or powdery mildew at site of infection

True

True or False: | Necrotrophic pathogens give the appearance of rust or powdery mildew at site of infection

False: | BIOTROPHIC pathogens give the appearance of rust or powdery mildew at site of infection

Some (all?) biotrophic pathogens maintain host cell viability. What does this mean?

They do not kill the plant, just compromise the growth. | Tissue invasion is limited so that plant remains unaware it is infected and no immune response is triggered.

Haustorial biotrophs produce haustoria. What are haustoria?

Growths in infected cells

What cells do Puccinia target?

``` Mesophyll cells (Hyphae grow into stomatal pore, infect mesophyll under epidermis) ```

What cells do Erysiphie target?

Epidermis of leaves

How might fungi break into cell walls of plants?

Via a mix of mechanical and chemical processes can drill into cell walls without affecting cell membrane. Fungi cell walls are much stronger than plants' cell walls so use pressure to force cell wall to break.

Fungi Flashcards

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