Mycology and Virology

• Mycology is the study of fungi, including their taxonomy, environmental impact, genetic, and biochemical properties

  
• General features of fungi:

  • Eukaryotic cell with nuclei and membrane-bound organelles
  • Possess a cell wall made of chitin
  • Reproduce by spores either sexually or asexually
  • Lack chlorophyll for photosynthesis
• Two phases of fungi:

  A. Yeasts:

  • Unicellular phase
  • Invasive in tissues at 35-37 degrees Celsius

  B. Molds:

  • Multicellular phase
  • Infective to humans at 25-30 degrees Celsius
• Dimorphism of Dimorphic fungi:

  • Exhibit either a yeast or mold form
  • Produce a mold form in room temperature and yeast form in body temperature
• Nutritional requirements of fungi:

  • Fungi are chemoheterotrophs
  • Grow best at room temperature
  • Grow best at a pH of 5.0
  • Most molds are aerobic while yeasts are facultative anaerobes
• Harmful effects of fungi:

  • Fungous allergies
  • Mycotoxicosis caused by fungal toxins like aflatoxin
  • Mycoses, infections of the human body caused by fungi
• Beneficial effects of fungi:

  1. Source of drugs like Penicillin and Cephalosporin

  2. Preparation of vaccines like Hepatitis B virus

  3. Induced Alcoholic fermentation

  4. Preparation of bread
• Hyphae are the long, thin, branching filaments that make up the body of the fungus, connected by septae, which are cross-walls
• Spores are the reproductive units of the fungus, produced in the sporangia at the ends of the hyphae, released for dispersion, germination, and growth into new hyphae
• Rhizoids are root-like structures that anchor the fungus to the ground and absorb nutrients
• Fragmentation is a form of asexual reproduction in fungi, where a new organism forms from a fragment of the parent organism
• A hypha is a filamentous structure of a fungus, oomycete, or actinobacterium, involved in nutrient absorption, growth, and reproduction
• Classification of hyphae:

  • Aerial Hyphae support reproductive structures like spores
  • Vegetative Hyphae (Thallus) for water and nutrient absorption
• Classification of hyphae:

  • Septate Hyphae have cross-walls
  • Aseptate Hyphae (Coenocytic Hyphae) lack cross-walls, seen in Zygomycetes like Rhizopus, Absidia, Mucor
• Mycelia are root-like structures of fungi consisting of branching, thread-like hyphae, occurring only in the mold phase
• Pseudohyphae occur in the yeast phase, with constricted septa, resulting from incomplete budding where cells elongate but fail to detach after division
• Dimorphism in fungi exhibits either a yeast or mold form, with mold form at room temperature and yeast form at body temperature
• Zygomycetes have aseptate/coenocytic hyphae, including members like Rhizopus, Absidia, Mucor, with rhizoids as root-like structures
• Hyaline hyphae are colorless fungal structures, while dematiaceous hyphae are dark and pigmented, including members like Curvularia, Alternaria, Phialophora, Exophiala, Fonsecaea
• Hyphal shapes:

  • Spiral: spirally coiled hyphae like Trichophyton mentagrophytes
  • Pectinate: short unilateral projections resembling a broken comb like Microsporum audouinii
  • Favic Chandelier: antler-like or chandelier hyphae like Trichophyton schoenleinii
  • Nodular organ: enlargement in the mycelium consisting of closely twisted hyphae like Microsporum canis
  • Racquet: swollen on one end, tapered on the other end, club-like shaped like Epidermophyton floccosum
• Diagnostics in mycology include routine tests like saline mount and KOH preparation, and special tests like India Ink or Nigrosin for Cryptococcus neoformans capsule identification
• Fungal culture media:

  • Sabouraud Dextrose Agar: general isolation medium for fungi
  • Dermatophyte Test Medium: primary recovery of Dermatophytes
  • Brain Heart Infusion: recovery for saprobic and pathogenic fungi
  • Birdseed Agar/Niger Seed Agar: identification of Cryptococcus neoformans
• Yeast is a single-celled organism that reproduces by budding, while mold is a multicellular organism that reproduces by spores

  
• Yeast is used in the production of bread, wine, and beer, while mold is used in the production of cheese and soy sauce

  
• Hyphae are the long, thin, branching filaments that make up the body of the fungus
• Hyphae are connected together by septae, which are cross-walls allowing controlled growth and branching
• Hyphae contain nuclei, the genetic material of the fungus
• Spores are the reproductive units of the fungus, produced in sporangia at the ends of hyphae, released for dispersion by wind or water, and can germinate into new hyphae forming colonies
• Rhizoids are root-like structures anchoring the fungus to the ground and absorbing nutrients
• Fragmentation is a form of asexual reproduction where a new organism forms from a fragment of the parent organism breaking off and developing into a new individual

  
• A hypha is a filamentous structure forming the mycelium of a fungus

  
• Hyphae are the basic unit of growth in filamentous fungi, involved in nutrient absorption, growth, and reproduction

  
• Hyphae are branching, filamentous structures forming the vegetative body of a fungus

  
• Different types of fungi and their growth at different temperatures:

  • Primary Recovery of Dermatophytes (Microsporum, Epidermophyton, Trichophyton) on Brain Heart Infusion
  • Birdseed Agar/ Niger Seed Agar for identification of Cryptococcus neoformans
  • Cornmeal Agar with Tween 80 for identification of Candida albicans by chlamydospore production
  • Cottonseed Agar for conversion of Blastomyces dermatitidis from mold to yeast form
  • Czapek's Agar for identification of Aspergillus spp. and Nocardia
  • Potato Dextrose Agar for pigment production by Trichophyton rubrum
  • Rice Medium Agar for identification of Microsporum audouinii
  • Urea Agar to differentiate Trichophyton mentagrophytes from Trichophyton rubrum

  
• Reproduction of Fungi: Asexual (Imperfect Fungi):

  • Production of Conidia following mitosis (conidiogenesis)
  • Asexual Reproduction is also known as Anamorph
  • Fragmentation of hyphae
  • Includes: Sporangiospore, Chlamydospore, Arthrospore, Macroconidia and microconidia, Blastospore, Phialides
• Types of Conidia:

  • Conidia are asexual spores produced in long chains or clusters by specialized vegetative hyphae known as conidiophore
  • Conidiophore may branch into secondary segments known as phialides

  1. Blastoconidia/ Blastospore: Daughter cells bud off from the mother cell and are pinched off

  2. Chlamydospores: Spherical shaped, thick-walled resistant spores formed by Candida spp.

  3. Arthrospores: Box-like or barrel in shape, produced by the fragmentation of hyphae into compartments

  4. Sporangiospore: Spores contained in sporangium or sacs, unique among fungi with nonseptate or coenocytic hyphae

  5. Macroconidia and microconidia:

  • Macroconidia: Large, septate, spindle-shaped, club-shaped
  • Microconidia: Smaller, round, pyriform-shaped, born singly or in graped-like structures along the hyphae
• Reproduction of Fungi: Sexual (Perfect Fungi):

  • Requires joining of 2 compatible nuclei following Meiosis
  • Also known as Telemorph
  • Includes Basidiospores, Ascospores, Zygospores, and Oospores

  1. Basidiospores: Spores contained in a club-shaped Basidium

  2. Ascospores: Produced in a round, sac-like ascus

  3. Zygospores: Fusion of 2 identical cells arising from the same hyphae

  4. Oospores: Fusion of cells from two separate and non-identical hyphae
• Other Fungal Structures:

  1. Cleistothecium: Large, round, multicellular structure that surrounds the asci and ascospores until the structure ruptures releasing the ascospores

  2. Columella: Sterile dome-shaped, swollen sporangiophore tip that extends into the sporangium

  3. Phialide: Vase-shaped or flask-shaped structure that produces phialoconidia
• Fungal Infections:

  A. Superficial Mycoses:

  • Malassezia furfur: Causes Tinea Versicolor or Pityriasis
  • Piedraia hortae: Causes Black Piedra
  • Trichosporon beigelii (Trichosporon cutaneum): Causes White Piedra
  • Hortaea werneckii: Causes Tinea Nigra

  B. Cutaneous Mycoses:

  • Affects Hair, Nails, and Skin
  • Disease: Tinea or Ringworm
  • Culture media: Dermatophyte Test Medium
  • Microsporum, Epidermophyton, Trichophyton