fungi

see also:

• tinea fungal infections
• microbiology
• clinically important bacteria
• antibiotics
• antifungal agents

• the fungus kingdom consisting of some 2.2 million to 3.8 million species is separated from plant, bacteria, protozoa and animal kingdoms by the presence of chitin-glucan complexes in their cell walls
• fungi are the principal decomposers in ecological systems and have fundamental roles in nutrient cycling and exchange in the environment
• most fungal structures are microscopic but they may become visibly noticeable when fruiting, either as mushrooms or as molds
• many species produce bioactive compounds called mycotoxins, such as alkaloids and polyketides, that are toxic to animals, including humans such as:
  • lethal amatoxins in some Amanita mushrooms
  • ergot alkaloids, which have a long history of causing serious epidemics of ergotism (St Anthony's Fire) in people consuming rye or related cereals contaminated with sclerotia of the ergot fungus, Claviceps purpurea
  • aflatoxins, which are insidious liver toxins and highly carcinogenic metabolites produced by certain Aspergillus species often growing in or on grains and nuts consumed by humans
  • ochratoxins
  • patulin
  • trichothecenes (e.g., T-2 mycotoxin)
  • fumonisins
  • psychedelic “magic mushrooms”
• certain fungi, in particular white-rot fungi, can even degrade insecticides, herbicides, pentachlorophenol, creosote, coal tars, and heavy fuels and turn them into carbon dioxide, water, and basic elements
• DNA analysis suggests that all fungi are descended from a most recent common ancestor that lived at least 1.2 to 1.5 billion years ago
• the earliest fossils possessing features typical of fungi date to the Paleoproterozoic era, some 2,400 million years ago (Ma), the estimated age of the oldest terrestrial lichen fossil is 415 million years
• lichens are a symbiotic relationship between fungi and photosynthetic algae or cyanobacteria
• many insects actively cultivate fungi for mutual benefit
• many fungi are parasites on plants, animals (including humans), and other fungi
• some are carnivorous
• fungi can be infected by other fungi, bacteria or mycoviruses

• many mushroom species are poisonous to humans and cause a range of reactions including slight digestive problems, allergic reactions, hallucinations, severe organ failure, and death.
• 112 known species of bioluminescent fungi (emit a greenish light at a wavelength of 520–530 nm), all of which are members of the order Agaricales (Basidiomycota) with one exceptional ascomycete belonging to the order Xylariales

• multicellular filaments or hyphae; aerobic;
• reproduce by:
  • spores:
    • sexual, small no's (eg.ascospores)
    • asexual, large no's (eg.conidia)
  • hyphal fragments;
• aspergillus
• Fusarium
• Penicillium
  • some of these are edible: blue vein, brie, camembert, gorgonzola or Roquefort cheeses

• cause various forms of tinea fungal infections
• hyphae/arthrospores; keratinolytic enzymes;
• arthrospore arrangement on hair:
  • small spore ectothrix (around base of hair)
  • large spore ectothrix
  • endothrix (chains of spores inside hair shaft)
• Microsporum
  • canis (green fluorescence; small ecto.; cats/dogs)
    • ⇒ tinea capitis/corporis most common cause)
  • audouini (green fluorescence; small ecto.; rare; humans
    • ⇒ tinea capitis rarely;
• Trichophyton
  • rubrum
    • ⇒ all forms tinea except capitis;
  • tonsurans (endo.; human)
    • ⇒ tinea capitis;
  • verrucosum (large spored ecto.; cattle)
    • ⇒ tinea barbae/corporis;
• Epidermophyton
  • floccosum
    • ⇒ tinea corporis/pedis/cruris;
• Pityrosporum (Malassezia) (yeast-like)

• Histoplasma
• Coccidiodes
• Parracoccidiodes
  • exist in mould form in the environment and when cultured at 25–30°C, and yeast form in human tissues and when cultured at 35–37°C
  • potentially pathogenic dimorphic fungi which can cause Paracoccidioidomycosis if spores inhaled from contaminated soil although only 1–2% of exposed individuals will develop clinical manifestations
  • endemic to South and Central America with up to 80% of cases occurring in Brazil
  • cases are mainly in rural farmers
  • 80-90% of symptomatic cases develop the chronic form and 90% of these patients are smokers:
    • disease develops over years, with pulmonary involvement including cough, dyspnoea, pulmonary fibrosis, bullae and pulmonary hypertension being the most common presentations
    • 50% develop chronic morbidity despite Rx including pulmonary fibrosis and emphysema, narrowing of the oral cavity, glottic stenosis, and sensory and motor neurologic manifestations
  • others have an acute or subacute form which develops weeks to months after exposure:
    • includes rapid progression of polymorphic skin lesions, lymphadenopathy, fever and anorexia:
  • an imported Australian case: https://www.mja.com.au/journal/2024/220/10/paracoccidioidomycosis-australian-case

• an informal sub-grouping of fungi
• the phylogenetic diversity of yeasts is shown by their placement in two separate phyla: the Ascomycota and the Basidiomycota. The budding yeasts or “true yeasts” are classified in the order Saccharomycetales, within the phylum Ascomycota.
• round/oval, unicellular, but sometimes form filaments as well;
• reproduce vegetatively by budding → blastospores;
• facultative anaerobes; form bacteria-like colonies on agar;
• may be Gram stained;
• can reduce sugars to carbon dioxide and ethanol hence some species such as S. cerevisiae and other Saccharomyces sp. are used in beer/wine making as well as baking
• Candida (budding; pseudohyphae)
• Torulopsis
• Cryptococcus (budding; v.large slimy polysacc.capsules; no hyphae)
• “probiotic gut yeasts”
  • Saccharomyces boulardii
    • genetically a grouping of S. cerevisiae strains, sharing >99% genomic relatedness, giving the synonym S. cerevisiae var. boulardii
    • has been shown to be nonpathogenic and nonsystemic (confined to the gut) in healthy people who ingest it HOWEVER in immunocompromised individuals, S. boulardii has been associated with fungaemia or localized infection, which may be fatal.
    • both S. boulardii and ordinary S. cerevisiae produce proteins that inhibit pathogenic bacteria and their toxins, specifically 63-kDa phosphatase pho8 (inhibiting E. coli endotoxin) and 54-kDa serine protease ysp3 (hydrolyzing C. difficile toxins A and B). An unidentified 120 kDa protein also inhibits changes in cAMP levels induced by cholera toxin.
    • S. boulardii encodes extra copies of yeast adhesion proteins called flocculins that help to stick to pathogenic bacteria and stop them from binding to the intestinal mucus
    • a 2015 meta-analysis of 21 randomised controlled trials (4780 participants) confirmed that S. boulardii is effective in reducing the risk of antibiotic-associated diarrhea in children and adults
    • reduces adverse gut effects of triple eradication Rx for H. pylori and marginally increases eradication rates

• a group of spore-forming unicellular organisms

• Ascomycota
  • “the sac fungi” or ascomycetes
  • Pezizomycotina
    • Dothideomycetes
      • Eurotiomycetes
        • Mycocaliciomycetidae
        • Sclerococcomycetidae
        • Coryneliomycetidae
        • Eurotiomycetidae
          • Onygenales (150mya)
          • Arachnomycetales
          • Eurotiales (green and blue moulds)
            • Aspergillaceae
              • see aspergillus
              • Aspergillus fumigatus is the most common cause of aspergillosis in individuals with an immunodeficiency.
        • Cryptocaliciomycetidae
        • Chaetothyriomycetidae
          • Chaetothyriales
            • Chaetothyriaceae
            • Coccodiniaceae
            • Cyphellophoraceae
            • Epibryaceae
            • Herpotrichiellaceae
              • Exophiala
                • has been implicated in causing 'saxophone lung' or hypersensitivity pneumonitis, a disease that can be contracted by woodwind instrumentalists
                • Exophiala jeanselmei
                  • causes maduromycosis which is a skin infection with black or brown macular lesions
                  • rare case of Exophiala jeanselmei pneumonia in an immunocompetent lady ¹⁾
                • Exophiala werneckii is the cause of tinea nigra
            • Lyrommataceae
            • Microtheliopsidaceae
            • Paracladophialophoraceae
            • Pyrenotrichaceae
            • Trichomeriaceae
          • Verrucariales
          • Phaeomoniellales
          • Pyrrenulales
  • Saccharomycotina (budding yeasts)
    • most of the yeasts
    • Saccharomycetales
      • Saccharomyces cerevisiae “yeast” converts carbohydrates to carbon dioxide and alcohols through the process of fermentation.
      • Candida albicans causes thrush
  • Taphrinomycotina
• Basidiomycota (fungi bearing spores on basidia)
  • Agaricomycotina
    • Tremellomycetes
      • many basidiomycete yeasts and some conspicuous jelly fungi
    • Dacrymycetes
      • a group of jelly fungi
    • Agaricomycetes
      • includes all the agarics (gilled mushrooms), bracket fungi, clavarioid fungi, corticioid fungi, and gasteroid fungi.
  • Pucciniomycotina
    • many are “rust fungi” in the Order Puccinales
  • Ustilaginomycotina
    • most (but not all) of the former smut fungi and the Exobasidiales.

• Chytridiomycota
• Neocallimastigomycota