Mycology

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Mycology

• Clinically Relevant Fungi

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The Significance of Fungi

• Decompose dead organisms and recycle their
  nutrients
• Form associations with roots of vascular plants,
  which help plants absorb water and minerals
• Used for food, in religious ceremonies, and in
  manufacture of foods and beverages
• Produce antibiotics
• Serve as important research tools
• 30 cause diseases of plants, animals, and humans
• Can spoil fruit, pickles, jams, and jellies

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Nutrition of Fungi

• Acquire nutrients by absorption
• Most are saprobes
• Some trap and kill microscopic soil-dwelling
  nematodes
• Haustoria allow some to derive nutrients from
  living plants and animals
• Most are aerobic some are anaerobic many yeasts
  are facultative anaerobes

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The Kingdom of the Fungae

• Myceteae
• Great variety and complexity
• Approximately 100,000 species
• Majority are unicellular or colonial

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The Kingdom of the Fungae

• Can be divided into
• three groups
• Yeasts
• Molds
• Macroscopic Fungi

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The Kingdom of the Fungae

• Can be divided into
• three groups
• Yeasts
• Round or oval shape
• Unique mode of asexual reproduction
• Some form pseudohyphae (false filaments)

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The Kingdom of the Fungae

• Can be divided into
• three groups
• Molds
• Long, threadlike cells
• Filamentous arrangement (hyphae)
• Some are dimorphic (yeast-like and filamentous
  forms exist)

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The Kingdom of the Fungae

• Macroscopic fungi
• Mushrooms, toad stools
• Bracket fungi
• Stink horns

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Fungi

• CHARACTERISTICS
• Parasitic or Saprophytic
• Eukaryotic
• Form Filaments termed hyphae
• Hyphae form mycelium septate or aseptate
• Cell wall composed of chitin
• or cellulose
• Slow to propagate
• Most are aerobic
• pH acidic

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Fungi

• FUNGUS multicellular, spore
• bearing, achlorophyllous
• organism which multiply
• sexually or asexually and
• whose usually filamentous
• somatic structure are septate
• or aseptate (coenocytic).
• The nutritional need of a
• fungus are facilitated by the
• enzymes cellulase and/or
• chitinase.

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Fungi

• All molds are fungi but all fungi
• are not molds--
• yeasts are fungi but they are
• unicellular and produce no aerial
• mycelium
• molds filamentous fungi that
• produce aerial mycelium
•  

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Fungi Somatic Structures

• Hyphae the tubelike filaments that constitute a
  mycelium.
•  
• Mycelia The somatic hairlike structures of a
  fungus. A mass of hyphae produced by some fungi.
•  

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Groups of Fungi

• LOWER FUNGI
•  
• Aseptate mycelia
• used to be called Phycomycetes 
• Saprophytic or parasitic
• Most primitive fungi
• Found mostly in soil, water, leaves
• Coenocytic Aseptate
• Produce asexual spore in sporangium

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Groups of Fungi

• Oomycetes
•  
• The oomycetes develop biflagellated zoospores
  with oppositely directed flagella. The mycelia
  is well developed, branched, aseptate or
  coenocytic. Sexual reproduction is oogamous.
  Some species are plant parasites of commerical
  crops such as grapes and potatoes. Some species
  are fish parasites.
•  
• Characteristic of Oomycetes
• water molds
• Some portion of life cycle is flagellated
• Cause fish disease and disease of commercial
  crops
• Plasmopara
• Phytophthora infestations--potato blight
•  Saplonegia fish infections

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Water Molds

• Differ from fungi in the following ways
• Have tubular cristae in their mitochondria
• Cell walls are of cellulose instead of chitin
• Spores have two flagella one whiplike and one
  tinsel-like
• Have true diploid thalli

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Groups of Fungi

• Zygomycetes
• Zygomycetes have well developed mycelia in which
  the hyphae are usually aseptate however, septa
  may form in older portions of the mycelia.
  Asexual spores are produced in sporangium.
  Sexual spores are produced after fusion of two
  gametes formed at hyphal tips.
•  
• Characteristics of Zygomycetes-
• predominantly terrestrial
• Breakdown organic molecules and are important in
  recycling
• Some are human pathogens
• Life cycle include both sexual and asexual
  reproduction
• characterized by zygospores
•  

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Groups of Fungi

• Chytridiomycetes responsible for recycling of
  nutrients in aquatic habitats.

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Groups of Fungi

• Trichomycetes are major
• parasites of insects.
•  

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Groups of Fungi

• HIGHER FUNGI
•  
• contain septate mycelia

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Groups of Fungi

• Ascomycetes possess septate hyphae and produce
  ascospores in sac-like structures known as asci.
  Karyogamy and meiosis occur in the developing
  ascus resulting in four haploid cells. These
  cells become ascospores. Mitosis occurs after
  meiosis and produces usually eight ascospores per
  ascus. Produces asexual conidiospores.
•  
• Two stages
• 1. Sexual or ascospore stage
• 2. Asexual or conidial stage
•  
• Characteristics of Ascomycetes
• Sac fungi also known as Perfect fungi
• Mostly plant pathogens
• Cell wall composed mostly of chitin
• produce sexual (ascospores) and asexual spores
  (conidiospores)

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Fungi

• Basidiomycetes
• The club fungi

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Groups of Fungi

• Basidiomycetes
•  
• Produce basidia, club-like structures in which
  karyogamy and meiosis occur. At maturity, two or
  four haploid basidiospores are produced on a
  basidium. The hyphae are septate and contain
  clamp connections. Include mushrooms,
  toadstools, rust, smuts, bracket fungi, puff
  balls, and birds nest fungi.
•  
• Basidiocarp
• pileus cap
• stipe stem
• lamellae gills

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Groups of Fungi

• Deuteromycetes
•  
• Include fungi whose sexual reproductive stages
  have never been observed. These fungi produce
  asexual conidia in abundance. The hyphae are
  septate.
•  
•  
• Characteristic of Deuteromycetes
•  
• Fungi imperfect most clinically important
• only reproduce asexually by conidiospores
• mycelium septate
• most pathogenic fungi in this group
• either had sexual stage and lost it or it has not
  been described
• all yeast that reproduce only be budding
•  

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Asexual Spores

• Sporangiospores
• Formed by successive cleavages within the
  sporangium
• Sporangium attached to the sporangiophore
• Released when the sporangium ruptures
• Conidiospores
• aka conidia
• Free spores
• Develop either by pinching off the tip of fertile
  hypha or by segmentation of a vegetative hypha

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Figure 5.19
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Deuteromycetes Pathogens

• Histoplasmosis, also known
• as Darling's disease, is a
• disease caused by the fungus
• Histoplasma capsulatum.
• Symptoms of this infection vary
• greatly, but the disease primarily
• affects the lungs.

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Deuteromycetes Pathogens

• Histoplasmosis
• Occasionally, other organs are
• affected this is called
• disseminated histoplasmosis,
• and it can be fatal if untreated.
• Histoplasmosis is common
• among AIDS patients because of
• their lowered immune system.
• Found in soil and associated with
• poultry feces and bat guano.

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Deuteromycetes Pathogens

• Sporothrix schenckii is the causative agent of
• Sporotrichosis or rose-handler's disease.
• Sporotrichosis is a subcutaneous infection and it
  
• starts following entry of the infecting fungus
• through the skin via a minor injury and may
• affect an otherwise healthy individual.
• Following entry, the infection may spread via the
  
• lymphatic route (nodular lymphangitis may
• develop). Patients infected with Sporothrix
• schenckii may be misdiagnosed as pyoderma
• gangrenosum due to the large ulcerations
• observed during the course of sporotrichosis.

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Deuteromycetes Pathogens

• Coccidioides immitis is a
• pathogenic fungust hat resides
• in the soil in certain parts of
• the southwestern United States.
• It can cause a disease called
• coccidioidomycosis (Valley Fever), and it
• is a rare cause of meningitis, mostly in
• Immunocompromised persons. It has
• been declared a select agent by both
• the U.S. Department of Health and
• Human Services and the U.S.
• Department of Agriculture and is
• considered a biosafety level 3 pathogen.
• Infects lungs and skin
• mainly.

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Deuteromycetes Pathogens

• Blastomyces s a fungal genus responsible for the
• medical condition blastomycosis.
• The most well known species of the genus is
• Blastomyces dermatitidis. B. dermatitidis is a
• dimorphic fungal pathogen, found primarily in the
  
• Mid-West and Northern United States and Canada.
• It exists in the soil in a filamentous form that
• produces spores directly upon the wall of the
• hyphae, lacking any kind of fruiting body to aid
  in
• aerosolization/dissemination of the spores.
• The natural reservoir of this organism in the
• environment is not clearly defined, but it seems
  to
• be associated with rivers and lakes. Blastomyces
  is
• endemic to the Mississippi and Ohio river valleys
  
• and the vicinity of the Great Lakes.

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Deuteromycetes Pathogens

• These agents infect human and animal hosts
• when they are inhaled. At the elevated
• temperature of 37C in a host, the
• fungus undergoes a phase transition to the
• pathogenic yeast form.
• Yeast form cells multiply in the lung and may
• cause disease in immuno-competent hosts,
• sometimes disseminating to the skin, central
• nervous system and bones.

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Dimorphism

• Some fungi exhibit different
• morphologies--grow as filamentous
• forms in soil and media, but in a suitable
• animal host form yeast. May display
• dimorphism just by changing environment
• and/or nutritional conditions.
•  
• Histoplasma capsulatum - mold on media at
• room temperature, yeast at 37C
• Candida albicans yeast at room temperature,
• pseudohyphae in body
•  
• 1. Dimorphism is advantageous because it allows
  them to reproduce more rapidly
• 2. Fends off immune response (encapsulate)
• 3. Allow them to obtain nutrition more rapidly

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Opportunistic Pathogens - Ringworm

• Ringworm is a fungal infection of the
• skin in humans and domestic animals
• such as sheep and cattle.
• Those that cause parasitic infection
• (dermatophytes) feed on keratin, the
• material found in the outer layer of
• skin, hair, and nails.
• These fungi thrive best on skin that is
• warm and moist.

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Opportunistic Pathogens - Ringworm

• Causative agents of Ringworm
• Dermatophytes
• Trichophyton spp
• Epidermophyton spp
• Microsporium spp

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Opportunistic Pathogens - Ringworm

• Causative agents of Ringworm
• Medically dermatophytes are
• classified as Tinea and the area they
• are infecting.

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Opportunistic Pathogens - Ringworm

• Tinea capitis
• Tinea pedis

• Tinea pubis
• Tinea corporis

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Opportunistic Pathogens - Ringworm

• Tinea ungum

• Tinea manum
• Tinea corporis

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Opportunistic Pathogens - Ringworm

• Malassezia furfur aka Tinea
• versicolor
• Mottled, discolored skin
• pigmentation is characteristic of s
• uperficial skin infection

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Opportunistic Pathogens - yeasts

• Candida albicans
• Causes oral and anal thrush
• Associated with yeast
• infections of vagina especially
• after a course of antibiotics.

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Opportunistic Pathogens - yeasts

• Cryptococcus neoformans
• Causes infections of brain,
• meninges, and skin
• Associated with
• immunocompromised individuals
• especially those with AIDS.

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Sick Building Syndrome

• Causative agents
• Stachybotrysis
• Cladiosporium
• Toxins produces by the fungi
• produce the clinical
• symptoms.

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Sick Building Syndrome

• Causative agents
• Water leaks lead to
• contamination

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Fungi in Symbiosis the Lichens
INSERT FIGURE 12.27
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• Fungi are Friends and Foes
• Not only involved in infections
• Allergies
• Poisoning
• Agricultural damage
• Benefits of fungi
• Decomposing organic matter and returning
  essential minerals to the soil
• Mycorrhizae increase the ability of plant roots
  to absorb water and nutrients
• Production of
• Antibiotics
• Alcohol
• Organic acids
• Vitamins