investigating growth

• We need to count microorganisms to see whether their growth/ reproduction has been affected by various factors.

  i.e. to find out the optimal temperature for a fermenter, or whether a bacteria can survive without a particular nutrient, or to test how effective an antibiotic/ antifungal medicine is.
• Counting microorganisms is difficult because they are so small.

  There are various methods of counting microorganisms/ estimating how many microorganisms are in a culture:

  • Cell count (using a haemocytometer)
  • Flow cytometry
  • Serial dilution and dilution plating
• We can use a cell count method by using a microscope and a sampling grid engraved onto a slide.
• Turbidity = how cloudy a solution is.

  The more turbid a solution the more particles there are in it.

  It can therefore be used as a proxy measurement for how many microorganisms there are in a broth.
• • Flow cytometry is where cells in a sample are passed one at a time through a tube.
  • A laser is shone at the cells as they pass.
  • The way the light scatters/reflects/transmits through the cells is detected.
  • This can provide an accurate cell count amongst many other things.
• Dilution plating is where you perform serial dilutions of a broth and culture the bacteria on agar plates until you can count individual colonies.