FOR #4 A & B I don't know if I did it correctly.....Pleasecheck & the other questions I'm having a heard time on.Thanks!
A. You have been given a tube of E. coli. You are askedto make 1 mL total volume of 10-1 dilution of thebacterial culture. Explain how you would do this.Show all necessary calculations.
____ ml cells  +   _____ ml water   = 1ml   (total volume)
V1 D1 X V2 D2
1 mL X 1 = V2 X 10^-1
V2 = 1 mL/10^-1 so V2 = 10 mL.
But because V1 is part of V2. The answer is: 10 mL-1 mL= 9 mL ofdiluent must be added.
V1 D1 X V2 D2
1 mL X 1 = V2 X 10^-2
V2 = 1 mL/10^-2 so V2 = 100 mL.
But because V1 is part of V2. The answer is: 100 mL-1 mL= 99 mL ofdiluent must be added.
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?
A. 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?
You take 0.05 mL of a culture of bacteria at a concentration of4 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?
A. 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?
A. 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:
C. This time, you see 10 times fewercolonies than you had expected to see.What could have gonewrong? How will you fix this problem?
  A bacterial sample has a concentration of 2x106 CFU/mL. Show a scheme of dilutions toobtain 30-300 colonies on a plate. Your scheme shouldcontain the volume of diluent (sterile water), volume of sampletransferred each time, the concentration of bacteria (CFU/mL) ineach dilution. You can assume you are plating 1 mL of the dilutionon plates of nutrient agar. See Figure 1 in protocol.
These are the results of the experiment described in theprotocol. From the data shown in the results section of StandardPlate Count protocol, calculate the concentration ofbacteria (CFU/mL) in the original sample of E.coli.  Show your calculations. Hint:remember that we don’t use plates that have less than 30 or morethan 300 colonies to do these calculations.
