Microbiology

• What are the three types of microbes?

  bacteria, fungi, viruses
• What are pathogens?

  Disease causing microorganisms
• How does bacteria reproduce?

  binary fission (splitting in two)
• How do viruses reproduce?

  By infecting living cells
• Example of bacteria


  Food poisoning
• Example of fungi


  Athlete's foot
• Example of virus


  Cold/ Flu
• Different classifications of bacteria

  -Size

  -Shape

  -staining properties (cell wall structure)

  -oxygen requirement

  -Grouping (e.g., single; pairs; chains)

  -metabolic, antigenic and genic features
• Different shapes of bacteria

  coccus, bacillus, spirillum
• Bacillus


  rod-shaped

  
  

  e.g., E.Coli
• coccus (prl) (cocci)


  spherical
• spirillum


  Corkscrew
• Obligate aerobes


  a microorganism that only grows in the presence of oxygen
• Obligate anaerobes


  a microorganism that can not grow in the presence of oxygen
• Facultative anaerobe


  a microorganism that grows best in the presence of oxygen but can grow without it
• What are the two types of cell wall structure?

  Gram positive bacteria and Gram negative bacteria
• What does gram positive bacteria stain?

  Violet/ purple
• What does gram negative bacteria stain?

  Pink
• Gram positive bacteria structure

  -Thicker peptidoglycan/ murein cell wall

  -No lipopolysaccharide layer
• Gram negative bacteria structure

  -Thinner peptidoglycan/ murein cell wall

  -Lipopolysaccharide layer
• What is the peptidoglycan layer made of?

  Polysaccharides and polypeptides
• What effect does having no lipopolysaccharide layer have on staining?

  Allows the stain to bind more effectively to peptidoglycan layer
• What does having no lipopolysaccharide layer in Gram positive bacteria make it more susceptible to?

  More susceptible to antibiotic, penicillin and the enzyme, lysozyme
• What does the lysozyme do to bacteria?

  hydrolyses the bonds holding the peptidoglycan molecules together
• What does penicillin do to bacteria?

  Prevents bonds inter-linking peptidoglycan molecules from forming

  Makes the cell walls weaker and more prone to collapse (by osmosis which bursts the cell)
• How do you control Gram negative bacteria?

  By a different class of antibiotics that interfere with the cells ability to make proteins
• What is the purpose of a lipopolysaccharide layer?

  Protects the cell and prevents dyes (crystal violet)
• Name the stages of Gram staining

  1) Fixation

  2) Crystal violet

  3) Iodine

  4) Decolouration (ethanol)

  5) Safranin
• On treatment with alcohol, what happens to the lipopolysaccharide layer?

  The gram negative cell wall lose their lipopolysaccharide layer (so crystal violet and iodine are washed from gram negative)

  Turns it colourless
• Why does Gram Positive bacteria remain purple after safranin (red counterstain)?


  Purple stain is stronger than red counterstain
• What are the two ways of counting bacteria?

  1) Directly (counting cells)

  2)Indirectly (measuring the turbidity of the cell)
• Viable counts


  describe living cells only
• Total counts


  Describe dead and living cells
• What is haemocytometry?


  Direct/ Total

  
  

  Known volume of sample placed on haemocytometry slide on high magnification

  Stains dead and living
• What is a pure culture?

  Only one type of microorganism
• What does a culture media contain?

  - carbon source (e.g., glucose)

  -Nitrogen

  -Water

  -Growth factors like vitamins

  -Agar
• Defined medium


  known ingredients
• Undefined medium


  not all components are known e.g., yeast extract
• Selective medium


  only allows certain bacteria to grow
• Requirements for growth of microorganisms

  - pH (slightly alkaline (7.4))

  - Temperature (metabolism is regulated by enzymes (25-45))

  - Oxygen requirement