Fungi

look at section 5 of BNF

what type of organisms are fungi- prokaryote or eukaryote?

eukaryote

why are there so many more antibacterials compared to antifungal drugs?

• humans and fungi are both eukaryotic

• :. chances of finding a target selective drug for fungi is much lower due to more similar cell structure

• makes treating fungal infections more challenging

what are the 3 kingdoms of organisms? which does fungi fall under?

• bacteria

• archaea

• eucarya → fungi falls into this category

how does fungi generate ATP?

• obtain source of reduced carbon via a sacrificient lifestyle i.e. feed off decaying matter

• this is used to make ATP using mitochondria

what is the study of fungi called?

mycology

why is studying fungi important?

• fungi are major decomposers in the environment :. important for recycling

• fungi can enter a parasitic state and cause disease in any life form

• fungi can be used for research e.g. on cell metabolism

what are the 2 basic fungal forms?

• yeast

• mould

describe the reproduction of yeast

• asexual: mainly reproduces via budding :. produces a genetically identical daughter cell that pinches off the surface of the parent cell

• sexual: fusion of two haploid cells to form a diploid zygote which undergoes meiosis to produce spores → genetically different

what are spores?

reproductive cells that are capable of developing into a new organism without fertilisation

describe the structure of mould as a basic fungal form

• formed from individual microscopic tubes called hyphae

• interconnecting series of hyphae are called myecelium = main body of mould

how does mould reproduce?

• asexual reproduction: mould produces genetically identical spores which are capable of dispersing through the air :. when they land in a suitable environment they germinate and grow into new mould colonies

• sexual reproduction: two compatible mating types of hyphae come into contact and fuse where meiosis occurs :. produces genetically diverse sexual spores

do spores cause disease?

not usually

• can cause allergy though

what are the different classifications of fungi?

• zygomycetes

• sac fungi (AKA ascomycetes)

• club fungi (AKA basidiomycetes)

• fungi imperfecti

describe the reproduction of zygomycetes

• asexual: hyphae grow until nutrient supply is depleted → after this spores are produced → these will disperse into the environment and germinate into new individuals

• sexual: 2 hyphae of different mating types (known as plus and minus) come together :. form zygote where haploid nuclei join to form diploid → cell wall thickens and meiosis occurs :. diploid to haploid reduction → haploid spores are released and asexual cycle continues

what are emerging fungal pathogens?

zygomycetes

what can ascomyctetes produce?

poisons

describe the sexual cycle of ascomycetes

• 2 compatible mating types of hyphae come into contact and undergo fusion of their cytoplasm and nuclei :. forms a diploid zygote

• diploid nucleus undergoes meiosis, followed by mitosis, to produce eight genetically diverse ascospores (= sexual spores) inside the ascus (= sac like structure)

• ascospores are released into the environment, where they can germinate and form new mycelium

describe the sexual cycle of basidiomycetes

• 2 compatible haploid hyphae meet and undergo fusion of their cytoplasm and nuceli :. forms diploid

• diploid organism continues to grow and eventually forms a basidiocarp (= fruiting bodies which have the cap, stalk and gill typical mushroom structure)

• inside gills, meiosis occurs :. diploid is reduced to haploid

• basidiospores form which are released into the environment → can disperse and germinate into new mycelium

why is sexual reproduction important?

more genetic diversity :. more adaptable to environment and better suited to deal with change

what are some of the properties of basidiomycetes?

hallucinogenic

describe the fungal cell composition. how does this affect drug action on fungi?

• cell wall mainly consists of chitin :. antibiotics that target peptidoglycan synthesis are not effective on fungi

• cell membranes contain ergosterol → different to humans which contain cholesterol :. target for antifungal drugs

describe the diamorphic nature of some fungi

refers to the ability of certain fungi to exist in two different forms → yeast at body temperature (37°C) and as mould at lower temperatures (25°C)

• adaptability allows them to survive in different environments

• dimorphic fungi are often pathogenic to humans.

what are the different types of infections fungi can result in?

depends on where fungi colonises and spreads

• cutaneous

• subcutaneous

• systemic

• opportunistic

describe the nature of cutaneous fungal infections

fungi infect keratinised structures e.g. hair, skin, nails

• athlete’s foot

describe the nature of subcutaneous fungal infections

• fungi are introduced into subcutaneous tissue via trauma

• typical infection leads to abscess formation → can appear as puss discharge through sinuses which can contain coloured granules

• immune response causes fungi to be surrounded by immune cells → only way out = via sinuses

• no effective drug treatment → need surgical intervention

describe the nature of systemic fungal infections

• result from inhalation of spores of dimorphic fungi :. yeast at body temperature

• most infections are asymptomatic and self limiting

• however can become more severe in immunocompromised patients → yeast form invades cells (e.g. WBCs) forming destructive lesions = fatal

describe the nature of opportunistic fungal infections

• mainly occurs in individuals who are immunocompromised → specifically those with impaired local or systemic defences

• often transmitted by inhalation :. causing lung infection

• often asymptomatic but dissemination (spread) is common to CNS :. meningitis

give an example of an opportunistic fungal infection

C. albicans

• forms normal microbiome in mucous membrane of GI tract

• overgrowth caused by immune system deficiency :. can cause thrush

what are some of the risk factors for yeast infections?

• pregnancy

• immunocompromised

• on oral contraceptives

• on antibiotics, chemotherapy or steroid therapy

• diabetic

what are common OTC produced used to treat fungal infections?

• fluconazole

• canesten