Microbiology

• Microbiology


  The study of organisms that are too small to be seen with the naked eye
• Why microbiology is studied

  • Disease prevention
  • Disease treatment
  • Stopping disease spread
  • Vaccines
• Types of microorganisms


  • Bacteria
  • Viruses
  • Protozea
  • Algae
  • Fungi
• Microorganisms first observed and described as little animals in rain water


  1674
• Link between microorganisms and disease established by Robert Koch


  1876
• Microscopes


  • Light microscopes used for bacteria, fungi, protozoa
  • Magnification: x4, x10, x40, x100 (all immersion)
  • Total magnification = Objective mag x Ocular lenses
• Cellular microorganisms


  Bacteria, fungi, protozoa
• Viruses


  Ultramicroscopic, require living organisms for growth and replication, specialized labs needed, samples taken from biopsies
• Fungi


  Free living in the environment, can be observed without visual aid, characteristic smell, spread through contact and wind spores
• Protozoa


  Unicellular eukaryotic organisms, mostly aquatic, can be intra or extracellular, visualised with light or electron microscopes
• Bacteria


  Prokaryotic, single-celled microorganisms, decomposers, mostly harmless but some pathogenic
• Bacterial cell components


  • Cell membrane
  • Cytoplasm
  • Nucleoid (contains DNA)
  • Ribosomes
  • Cell envelope (maintains shape, protects from lysis)
  • Capsule (protects, adheres to surfaces)
  • Cell wall (aids structure and support)
• Gram staining

  Crystal violet, iodine, alcohol, safranine used to differentiate between gram positive (thick peptidoglycan layer) and gram negative (thin peptidoglycan, outer membrane) bacteria
• Bacterial growth requirements

  • Water (90% water required for metabolic reactions)
  • Nutrients (carbon, hydrogen, nitrogen, phosphorus, iron for growth)
  • Oxygen (obligate aerobes, obligate anaerobes, microaerophilic, facultative anaerobes)
  • Temperature (psychrophilic, mesophilic, thermophilic)
  • pH (acidophilic, neutrophilic, alkaliphilic)
• Bacterial spores


  Formed when conditions become unfavourable, allow bacteria to survive heat, drying, chemicals
• Bacterial toxins


  • Endotoxins (released from outer membrane of gram negative bacteria when they die, cause endotoxic shock)
  • Exotoxins (soluble toxins secreted by live bacteria, can poison host animals)
• Bacterial diseases


  • Gram positive cocci: Staphylococcus aureus (mastitis), Streptococcus pyogenes (sore throat)
  • Gram positive spore forming bacilli: Bacillus anthracis (anthrax), Clostridium tetani (tetanus)
  • Gram negative aerobic bacilli: Pseudomonas aeruginosa (infections), Brucella abortus (zoonotic abortion), Bordetella bronchiseptica (kennel cough)
  • Gram negative coccobacilli: Pasteurella multocida (pneumonia)
• Bacterial growth


  1. Binary fission (asexual replication)

  2. Mutations can occur in DNA replication (e.g. MRSA)

  3. Bacterial conjugation (transfer of plasmids between cells)

  4. Lag phase (adaptation to new environment)

  5. Log/exponential phase (maximal growth)

  6. Deceleration phase (growth rate declines)

  7. Stationary phase (reproductive rate equals death rate)

  8. Death phase (death rate exceeds growth rate)
• Open vs closed systems

  Open systems constantly exchange matter, closed systems do not
• Agar plates


  Permissive (allow growth), selective (encourage desired bacteria), differential (identify types of bacteria), enriched (extra nutrients)
• Types of agar

  • Blood agar
  • MacConkey agar
  • Mannitol salt agar
  • Brilliant green agar
• Nutrient broth


  Complex liquid media, growth determined by turbidity
• Fungi


  • Eukaryotic, unicellular or multicellular, reproduce sexually and asexually using spores
  • Hyphae - branching filaments, septate (distinct cell walls) or aseptate (no walls)
  • Mycelium - mass of intertwined hyphae
  • Conidia - spores formed by mitotic division in hyphae
• Asexual reproduction in fungi

  1. Spores are released

  2. Spores germinate

  3. Offspring are identical to parent
• Sexual reproduction in fungi

  1. Hyphae of two organisms fuse

  2. Azygote is produced

  3. Azygote undergoes meiosis

  4. Spores are produced

  5. Offspring have genetic characteristics from both parents
• Hyphae


  • Branching filaments
  • Larger than bacterial cells
  • Require light microscope to see
• Types of hyphae


  • Septate
  • Aseptate
• Septate hyphae


  Each cell has distinct wall between it and neighbouring cell, has own organelles and nucleus, have pores in wall to allow movement of nutrients, pores can close if damaged to prevent damage to whole cell
• Aseptate hyphae


  Internally no walls to separate, cytoplasm free flowing, primitive mould
• Growth of hyphae


  1. Hyphae intertwine and form a mass called mycelium

  2. Mitotic divisions in hyphae produce identical clones to increase size of organism

  3. Conidiospores produced to increase spores and number of organisms
• Yeasts


  • Unicellular, oval or spherical cells
  • Colonies often look similar to bacterial colonies
• Yeast reproduction


  • Asexual reproduction by budding - yeast cell produces a bud that eventually breaks away from parent cell
  • Sexual reproduction - 2 yeast cells fuse to form an ascus containing 1-8 ascospores which are released
• Fungal growth requirements


  • Moisture/humidity
  • Nutrients - organic matter
  • Atmosphere - moulds are aerobes, yeasts are facultative anaerobes
  • Warmth - usually ambient temperature
  • pH
• Sabouraud dextrose agar


  Culture medium used for fungi, high sugar concentration, mildly acidic
• Pathogenic fungi are widespread in the environment
• Opportunistic pathogens


  Not infectious under normal conditions, but can cause infection if conditions change e.g. ageing, illness, injuries, antibiotics
• Fungal diseases


  • Candidiasis
  • Malassezia dermatitis
  • Dermatophytosis
  • Aspergillosis
• Candidiasis


  Caused by Candida, affects mouth, nose, ear, skin (warm, damp places)
• Malassezia dermatitis


  Skin infection caused by Malassezia pachydermatitis, causes erythema, pruritic, primary exudate, musty/yeasty
• Dermatophytosis


  Skin infection known as ringworm, caused by Microsporum (humans) or Trichophyton (animals), causes classic ring-shaped lesion, alopecia, crusting