#4. You have been given a tube of E. coli. You areasked to make 1 mL total volume of 10-1 dilution of thebacterial culture. Explain how you would do this.Show all necessary calculations.
#5 You have bacteria at a concentration of 5 x 108CFU/mL. You spread 1 mL of this sample on an agar plate to obtainisolated colonies. How many colonies do you expect to findthe next day after incubation at 370C? Can you countthese colonies? Can you use this plate for determiningconcentration?
#6. You have bacteria at a concentration of 1 x 103CFU/mL (in real life – you don’t know this, but we are just workingon math skills here). You transfer 1 mL of this sample into 9 mL ofwater and then spread 1 mL on a plate of agar. How manycolonies do you expect to find the next day after incubation at370C? Can you count these colonies? Can you use thisplate for determining concentration?
#7 You take 0.05 mL of a culture of bacteria at a concentrationof 4 x 107 CFU/mL, and add 4.95 mL of water to it.What is the dilution that you have performed? What is theconcentration of bacteria (CFU/mL) in the dilutedculture?
#8. You have diluted a sample by 1000 fold (1/1000) and plated 1mL on an agar plate. You observe 55 colonies. What was theconcentration of the original sample in CFU/mL?
#9. A bacterial sample has a concentration of 3x107CFU/mL. You make serial dilutions of 10-3followed by 10-2 and 10-1 dilutions. Youfinally plate 1 mL of the last dilution on an agar plate andincubate it at 370C.  What is thetotal dilution? How many colonies do you expect tosee on the plate?
Total dilution:
# of colonies expected on plate:
#10. This time, you see 10 timesfewer colonies than you had expected to see.What could havegone wrong? How will you fix this problem?
