Nature of Fungi

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Nature of Fungi
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Taxonomy

• Superkingdom Eukaryoteae
• Kingdom Fungi
• Cells possess a cell wall
• Composed of chitin
• Are not plants not capable of photosynthesis
• Heterotrophic Saprophytes

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Mycology The study of Fungi

• Characteristics of Fungi
• Unicellular or multicellular filamentous
  eucaryotic organisms possessing both
  asexual(anamorphic) and sexual(teleomorphic)
  means of reproduction
• Unicelluar fungi are known as yeasts
• single-celled fungi reproduce asexually by
  mitosis
• Since the daughter cells are unequal in size, the
  smaller cell is called a bud, or blastospore
  Thus, the process is called budding
• Multicellular fungi are known as molds
• Hypha basic morphological unit of a mold
  fungus
• septate vs. aseptate
• vegetative vs. aerial(reproductive)
• mycelia mass of hyphae
• thallus the complete body of fungal growth
• Fungal Cells (yeast and molds)
• eucaryotic cells having a complex cell membrane
  called a plasmalemma which is a
  phosolipid-protein bilayer that contained the
  sterol, ergosterol.
• multilayered cell wall composed of chitin, a
  polymer of N-acetylglucosaminae, and many
  polysaccharide and protein derivatives
• Three health effects of fungi allergens,
  poisons, infections

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Definition

• Unicellular and multicellular eucaryotic
  organisms which reproduce both sexually and
  asexually.
• Unicellular yeasts
• Multicellular molds

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Mycology The study of Fungi

• Fungal Metabolism
• most fungi are aerobes, but some carry out
  anaerobic fermentation
• vegetative cells are heterotrophic having much
  metabolic versatility this accounts for their
  significant role in destruction of foods and
  recycling of nutrients
• pathogenic fungus are often dimorphic they grow
  as molds at 25 C and as yeasts at 37 C
• Fungi as human/animal pathogens mycoses
• with only a few exceptions, the human-fungus
  interaction is accidental
• only unicellular fungi, Candida, are considered
  normal microflora
• some fungi have increased virulence due to long
  term association with humans this is mostly as
  survival adaptation.
• Classification of Fungi
• Kingdom Fungi(Mycetae)
• Phylum/Class Zygomycota, Dikaryomycota,
  Deuteromycotina
• This classificatin is based most on the type of
  spores formed during sexual reproduction

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Unicellular Fungi

• Yeasts
• Unicellular eukaryotes
• Reproduce asexually by mitosis
• Telophase is unequal thus, yielding the parent
  cell plus a blastospore or bud sometimes called
  budding
• Some form pseudohyphae
• Sexual Reproduction
• Two cells fuse forming a diploid cell
• Diploid cell divides by meiosis yielding more
  haploid vegetative cells

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Multicellular Fungi

• Molds
• Multicellular many cells that are the same
• No cellular differentiation or specialization
• Hypha the basis unit of a multicellular fungus
• Asexual Reproduction specialized hyphae produce
  spores by mitosis spores conidia
• Sexual Reproduction specialized cells fuse
  together the resulting cells then go thru meiosis

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Dimorphic Fungi

• Fungi which exhibit both vegetative stages
• i.e. yeast phase and mold phase
• Some environment variable like temperature
  determines which phase
• Many pathogenic fungi are dimorphic
• Unicelluar at 37 C in the human body
• Muticellular at 25 c room temperature in the lab

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Effects on Human Health

• Allergens
• The asexual spores of many environmental fungi
  are very allergenic
• Stimulating type 1 hypersensitivity (atopy)
• Poisons
• Some of the most toxic substances known to
  science come from fungi
• When ingested are highly fatal
• Infections
• Vegetative cells of some fungi can enter the
  human tissues where they grow causes cellular
  changes resulting in disease

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Superficial Fungi

• Pityriasis versicolora is a superficial mycosis
  which appears on the upper torso, arms, and
  abdomen as hyper/hypo pigmented macular lesions
  which scale leaving the area looking dry and
  chalky
• Malassezia furfur is a lipophilic yeast which is
  part of the normal microflora of the skin grows
  mostly a a yeast, but sometime produces a hyphal
  form.
• grow in the skin is activated by certain
  predilecting factors like exposure to sunlight,
  etc.
• organism is identified in KOH preparation of the
  white, chalky scales organism appears a yeast
  cells among hypae

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Cutaneous Fungi-Dermatophytes

• Dermatophyte Fungi - are mold fungi which grow
  in tissues containing keratin Thus, they are
  limited to skin, hair and nails.
• cellular immune response to the presence of fungi
  in the skin evokes an inflammatory response often
  described as ringworm or tinea
• infections are often classified by the area
  affected such as tinea capitis, tinea pedis,
  tinea manus, tinea ungium, etc.
• there are three main dermatophyte genera which
  infect humans
• Trichophyton
• Epidermophyton
• Microsporium
• species within these genera are grouped based
  upon their source
• anthropophilic humans
• zoophilic animals
• geophilic soil
• dermatophytes are diagnosed by finding septate
  hypha and asexual(anamorphic) spores in the
  scraping of infected tissue.
• specific identification of the fungi is made by
  culture

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Subcutaneous Fungi- Mycosis

• Lymphocutaneous Sporotrichosis nodular and
  ulcerative lesions which develop along the
  lymph channels which drain the primary site of
  inoculation when the lymph gland is infected,
  the fungus disseminates to other areas
• Sporothrix schenckii a dimorphic fungus
• fungus grow in soil and on plants and spores are
  inoculated into subcutaneous tissues by thorns
  and sharp needle of certain plants, like roses.
• Diagnosis is based upon finding yeast cells in
  lymphatic fluid from lesions
• In the laboratory at 25 C, characteristic
  colonies containing delicate branching hyphae
  with unique rosette conidia

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Systemic Fungi Systemic Mycoses

• Histoplamosis acute necrotizing, caseous
  granuloma of the lungs in immunocompromised
  people or those exposed to high infectious
  dose, the yeast cells invade the mediastinal and
  hilar lymph nodes and disseminate via
  macrophages to the liver and spleen in
  immunocompetent people the cellular immune
  response limits the spread of the yeast and
  confines the infection to mild flu-like
  symptoms most primary infections are
  asymptomatic has many features similar to
  tuberculosis
• Histophasma capsulatum dimorphic fungus found in
  nature mutiplies extensively in area where
  bird feces accumulate
• Epidemiology endemic geographical area
  macroconidia(spores) are inhalated and taken into
  the lungs
• Blastomycosis chronic granulomatous ans
  suppurative disease of the lungs resulting in
  small areas of pulmonary consolidation when
  confined to the lungs resolution results in
  scarring dissemiation involves the skin,
  bones,
• Blastomyces dermatiditis dimorphic fungus found
  in nature
• Epidemiology broad geographic area with source
  unknown

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Systemic Fungi - Systemic Mycoses

• Coccidioidomycosis chronic, necrotizing mycotic
  infection of the lungs which pathologically
  resembles tuberculosis begins as a
  bronchopneumonia with its inflammatory
  infiltrate disseminates in immunocompromised
  people to many sites including skin, bones,
  meninges,liver, spleen. symptoms range from
  asymptomatic to mild respiratory symptoms to
  diverse set of symptoms associated with the
  affected areas another great imitator
• Coccidioides immitis dimorhic fungus which grows
  in the soil of the S.W. United States spores
  called arthrospores are inhaled into the alveoli
  and terminal bronchioles where they enlarge into
  spherules spherules fill with
  endospores(yeast-like cells) which are released
  to form more spherules
• Epidemiology
• Diagnosis

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Systemic Fungi Systemic Mycoses

• Cryptococcosis primary disease of the lungs with
  gramulomas and consolidation readily spreads
  to the meninges and brain causing
  meningoencephalitis
• Cryptococcus neoformans only systemic fungus
  which is not dimophic its is a highly
  encapsulated yeast which accounts for its
  virulence
• Epidemiology
• Diagnosis

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Opportunistic Fungi Mycoses

• Candidia albicans
• a common unicelluar fungus which is part of the
  flora of the oral cavity, vagina, and
  gastrointestinal tract in this setting in
  becomes an opportunist especially in
  immunocompromised people
• in culture, it grow as blastospores,
  pseudohyphae, and septate hyphae
• candidiasis the collective term for infection
  involving Candida
• cutaneous
• vaginal
• systemic
• Aspergillus fumigatus/ A. flavus
• Pneumocystis carnii