Lecture C1 - Fungal Pathogens Flashcards
What are fungi?
They’re own unique, living organisms. Can be single celled microorganisms but they are eukaryotic cells.
More in common with animal cells than to plant cells on a cellular level.
Describe the fungal cell wall.
Only thing protecting the single celled organism from everything.
Dense.
Ergosterol (like cholesterol) is the fungi’s sterol.
Chitin - strong, in the cell membrane.
Attached to chitin is a range of sugar molecules from the inner wall.
Mannan and proteins - form the outside of the wall.
What are the 4 major groups of fungi?
Single celled yeasts
Multicellular filamentous fungi (moulds)
Dimorphic fungi
Macroscopic filamentous fungi that form large fruiting bodies (mushrooms).
What does fungi have an association with?
Fungi and other plants - fungi provides plants with essential nutrients.
What are heterotrophs?
Organisms that can’t synthesise its own food, gets its food from other sources.
Fungi do this via an array of enzymes that are secreted into the environment and break it down into smaller molecules that the fungi can use for its own food source.
Name some benefits of fungi.
Brewers yeast - Saccharomyces cerevisiae
Filamentous fungi for food production, medicines, insecticides.
Describe the fungal morphology of filamentous fungi (moulds).
Moulds form multicellular filaments known as hyphae.
Hyphae grow by apical extensions of their filaments, branching is common.
Continued growth leads to a complex network of hyphae called mycelium.
Specialised hyphae are produced to allow vegetative reproduction of spores or conidia.
Spores are released into the environment to allow for hyphae to grow in a different place, release of spores allows for germination and reproduction of filamentous fungi.
What are some superficial mycoses?
Infections of the skin or mucous membranes - usually not life threatening.
Cutaneous (on the skin) - athletes foot, ringworm
Subcutaneous (just inside the skin) - mycetoma, sporotrichosis.
Describe systemic mycoses.
Infections inside the internal organs, usually serious and can be life threatening.
Primary systemic infections - can infect healthy hosts, usually dimorphic fungi, can switch their morphology, usually temperature dependent.
Opportunistic systemic infections - only infect immunocompromised hosts, responsible for over a million deaths each year.
Describe sporotrichosis.
Nastier than cutaneous mycoses.
Dimorphic fungus - temperature induced change in the morphology of the fungus. 25 degrees is the environmental, not hazardous form, 37 degrees is the diseased form.
Characterised by development of skin lesions.
Spread through the lymphatic system that drains away from the initial site of inoculations so the infection can present with subcutaneous nodules appearing along the proximal lymphatic system.
Describe cutaneous mycoses.
High prevalence.
Each infection is named in relation to where on the body it affects.
The term tine is used for fungal infections that affect skin, hair and nails.
Fungus responsible for athletes foot and nail infections is Trichophyton rubric - a filamentous fungi forming hyphae with microconidia.
Risk factors are decreased immune response, age. diabetes, poor circulation and corticosteroid use.
Describe mycetoma.
Barefoot walking populations of tropical and subtropical countries are most at risk.
Disease initiated after a minor trauma (cut) that allows causative fungus entry into the subcutaneous tissue.
Slow progressive formation of hard, painless lesions, as they are painless treatment not usually sought after so it can progress further and can begin to infect the bone, this is when amputation is required.
What are some examples of systemic fungal infections?
Blastomyces dermatitidis
Coccidioses immitis
Histoplasma capsulatum
Paracoccidioides brasillensis
All endemic
All dimorphic
All infect lung following inhalation and produce conidia and spores
All can infect healthy humans.
Describe histoplasmosis.
Responsible fungus is Histoplasma capsulatum.
Dimorphic, 25 degrees it is in hyphen form (produces conidia) and 37 degrees is a small budding yeast.
The fungus can replicate inside the macrophage, allowing it to spread around the body easier.
Most infected people have no symptoms or symptoms that spontaneously clear, not generally life threatening.
Describe coccidioidomycosis.
Responsible fungi is Coccidioides immitis and Coccidioides posadasii.
Found in soil and low moisture environments, growing as a filamentous fungus.
Mycelia produce square, spore like cells called arthroconidia. One spore is sufficient to cause valley fever.
Once in the host it begins ti get larger and produces yeast like structures called spherule that keep getting larger and larger until they burst and release endospores.
Hard to get rid of but not light threatening.
