Fungal Morphology

• Mycology

  The study of fungi
• The term "mycology" is derived from the Greek word "mykos" meaning fungi
• Fungal kingdom

  • Most organisms normally live a saprophytic existence in nature, enriched by nitrogenous matter
• Morphologic features of the fungi

  • The presence of chitin (a long chain polymer of N – acetylglucosamine) in the cell wall
  • The presence of ergosterol in the cell membrane
  • Reproduction by means of spores, produced either asexually or sexually
  • The lack of chrolophyll
  • Lack of susceptibility to antibacterial antibiotics
  • They are chemoheterotrophs (require organic compounds for both carbon and energy sources)

  
• Fungi Perfecti

  • Fungi that have recognized sexual reproductive structures
  • Phylum: Zygomycetes, Ascomycetes, & Basidiomycetes
• Fungi Imperfecti

  • Fungi that lack recognized sexual reproductive structure
  • Phylum Deuteromycetes
  • Telemorph – sexual phase of fungi imperfecti and reclassified into one of the other phyla
  • Anamorph – asexual name used to describe a fungal species in the laboratory

  
• Fungal cell wall

  • A stratified structure consisting of chitinous microfibrils embedded in a matrix of small polysaccharides, proteins, lipids, inorganic salts, and pigments
  • CHITIN is a (β1-4) – linked polymer of N-acetyl-D-glucosamine
  • Produced in the cytosol

  
• Fungal plasma membranes

  • Similar to mammalian plasma membranes, differing in having the nonpolar sterol ergosterol, rather than cholesterol, as the principal sterol
  • The plasma membrane regulates the passage of materials into and out of the cell by being selectively permeable

  
• Fungal microtubules

  • Composed of the protein tubulin
  • Long, hollow cylinders approximately 25 nm in diameter that occur in the cytoplasm as a component of larger structures
  • The principal components of the spindle fibers, which assist in the movement of chromosomes during mitosis and meiosis

  
• Many pathogenic fungi are dimorphic, forming hyphae at ambient temperatures but yeasts at body temperature
• Modes of Reproduction

  • Fission of somatic cells
  • Budding of somatic cells or spores
  • Segmentation or disjointing hyphal cell
  • Spore formation
• Types of Spores

  • Sporangiospores
  • Conidiospores or conidia
  • Oidia or Arthrospores
  • Chlamydospores
  • Blastospores

  
• Sexual reproduction in fungi

  • Carried out by fusion of the compatible nuclei of two parent cells
  • Sex organelles of fungi if they are present, are called gametangia
  • Male gametangia: antheridia
  • Female gametangia: oogonia

  
• Basic structural unit of molds

  • The main body of the fungi that is made up of fine, branching, usually colorless threads
  • Mass or bundle of hyphae
  • Vegetative mycelium
  • Aerial mycelium
  • Fertile mycelium are aerial hyphae that bear reproductive structures such as conidia or sporangia
  • Have cross-walls (septate or aseptate) containing pores for communication
  • Conidiophores are septate portion of a combination of septate and aseptate
  • Sparsely septate (coenocytic) are aseptate with part that is septate (occasional cross-walls)

  
• Hyphae

  • Branch at acute angles such as Aspergillus species with narrow hyphae
  • Presence of a constriction at the junction
  • Restriction in size of the daughter cell
• Zygomycetes

  • Mucor
  • Rhizopus
  • Lichteimia
  • Absidia
• Zygomycetes

  • Produce large, ribbonlike hyphae that are irregular in diameter with occasional septa
  • Specific identification is the saclike fruiting structure (sporangia) whit internally spherical, yellow or brown spores (sporangiosphore)

  
• Dermatophytes

  • Trichophyton
  • Microsporum
  • Epidermophyton
• Trichophyton

  Usually grows on hair, skin and nails
• Microsporum

  Invades the hair and skin
• Epidermophyton

  Invades the skin and nails
• Trichophyton species

  • Smooth, club-shaped, thin-walled macroconidia with 3 – 8 septa
  • Macroconidia are borne singly at the terminal ends of hyphae or on short conidiophores
  • Microconidia ("birds on a fence") predominate and usually are spherical, pyriform, or clavate
  • T. rubrum - Slow-growing produces flat or heaped-up colony, white to reddish, with cottony or velvety appearance, Cherry-red on reverse side of colony
  • T. mentagrophytes - Downy variety is recovered from patients with tinea pedis, Granular variety is recovered from lesions acquired by animal contact, Rapid growing with cream-colored to yellow, cottony or downy colony
• Microsporum species

  • Recognized by the presence of large, spindle-shaped, echinulate, rough-walled macroconidia with thick walls containing 4 or more septa
  • Exception: M. nanum = produces macroconidia having two cells
  • Develop either rapidly or slowly producing aerial hyphae that may be velvety, powdery, glabrous, or cotoony
  • Color: whitish, buff, to cinnamon brown

  
• Epidermophyton species

  • E. floccosum is the only member
  • Common cause if tinea cruris and tinea pedis
  • Grows slowly; growth appears olive green to khaki, with periphery surrounded by a dull orange brown
  • Microscopic: Numerous, thin-walled, club-shaped, multiseptated macroconidia, Absent microconidia, Spiral hyphae
  • The absent microconidia is useful in differentiating the organism from Microsporum spp.
• Saprophytic fungi

  • Aspergillus species
  • Fusarium species
  • Penicillium species
• Aspergillus species

  • Rapidly growing that produces a fluffy to granular, white to blue-green colony
  • Mature sporulating colonies most often have blue-green, powdery appearance
  • Usually have "feet cell"
  • Aspergillus fumigatus - Characterized by the presence of septate hyphae and short or long conidiophores with a characteristic "foot cell"
  • Foot cell is T or L shaped at the base of the conidiophores (but not a separate cell)
  • The tip of the conidiophore expands into a large, dome-shaped vesicle with bot
• E. floccosum

  The only member of the species
• E. floccosum

  • Common cause of tinea cruris and tinea pedis
  • Grows slowly
  • Growth appears olive green to khaki, with periphery surrounded by a dull orange brown
• E. floccosum microscopic features

  • Numerous, thin-walled, club-shaped, multiseptated macroconidia
  • Absent microconidia
  • Spiral hyphae

  
• Absent microconidia

  Useful in differentiating the organism from Microsporum spp.
• Most fungi are saprobes
• Saprobic fungi

  • Aspergillus species
  • Fusarium species
  • Penicillium species
• Aspergillus species

  • Rapidly growing that produces a fluffy to granular, white to blue-green colony
  • Mature sporulating colonies most often have blue-green, powdery appearance
  • Usually have "feet cell"
• Aspergillus fumigatus

  • Characterized by the presence of septate hyphae and short or long conidiophores with a characteristic "foot cell"
  • Foot cell is T or L shaped at the base of the conidiophores (but not a separate cell)
  • The tip of the conidiophore expands into a large, dome-shaped vesicle with bottle-shaped phialides covering the upper half or two thirds of its surface
• Aspergillus flavus

  • More rapidly growing species with yellow-green colony
  • Microscopically with globose vesicle
  • Phialides give rise to short chains of yellow-orange elliptical or spherical conidia
• Aspergillus niger

  • Grown usually between 2 and 6 days
  • Colony color initially is yellow and soon becomes black, dotted surface as the colony matures
  • Produces darkly pigmented, roughened spores
  • Microscopically: Septate hyphae, long conidiophores supporting spherical vesicles giving rise to large metulae and smaller phialides
  • The entire surface is involved in sporulation

  
• Fusarium species


  • Grow rapidly (2-5 days)
  • Fluffy to cottony colony
  • Small and septate hyphae with phialides producing either single-celled microconidia
  • Macroconidia are sickle or boat-shaped containing numerous septate
• Penicillium species

  • Colonies are most commonly of green or blue-green (pink or other colors may be seen)
  • Surface of colony may be velvety to powdery (due to conidia)
  • Hyphae are hyaline and septate and produce a brushlike conidiphores which produces a flask-like phialides
• Unicellular organisms

  • Round to oval (2-60um)
  • Reproduce asexually by blastoconidia formation (budding)
  • Reproduce sexually by production of ascospores or basidiospores
  • Far less common, some yeasts reproduce asexually through binary fission
• Size of the yeast

  • Presence or absence of capsule
  • Broad-based vs narrow-necked budding