culturing microorganisms

• what are the two main risks associated with culturing microorganisms?

  • mutation can take place, making the strain pathogenic
  • contamination with pathogenic organisms from the environment
• why are aseptic techniques important?

  • to prevent the growth of harmful/unwanted microorganisms/pathogens
  • therefore preventing contamination
• state the process of inoculating broth

  • make a suspension of bacteria to be grown
  • nutrient broth prepared
  • mix a known volume of bacteria suspension and add to nutrient broth by inoculation
  • stopper the flask with cotton wool to prevent contamination from the air
  • incubate at suitable temperature, shake regularly to aerate bacteria to provide oxygen
• state the process of inoculating agar

  • wire inoculating loop held in a Bunsen burner until it glows red hot
  • doesn't touch any surfaces to avoid contamination
  • loop dipped in bacterial suspension
  • remove petri dish lid and apply bacteria, making zig zag applications across agar surface
  • petri dish sealed lightly with cello tape so oxygen can enter, preventing the growth of anaerobic bacteria
  • incubate at suitable temperature
• state two techniques for culturing microorganisms

  • inoculating agar
  • inoculating broth
• state the individual stages of a bacterial growth phase

  • lag phase
  • log phase
  • stationary phase
  • death phase

  
• what are the limiting factors preventing exponential growth in a culture of bacteria?

  • nutrients available- more competition for food as population grows
  • oxygen levels- demand for respiratory oxygen increases
  • temperature- affects enzymes involved
  • build up of waste- can poison and kill culture
  • change in pH- low pH affects enzyme activity
• what does a serial dilution look like?

  Series of tubes with decreasing concentrations of bacteria

  
• at what point in a population growth curve for bacteria is death rate the highest?

  the stationary phase