You are to microbiologist for the Minnesota Department of Health. A sample of âsuspectâ ground beef from Jimboâs Grocery in Minneapolis is brought to your lab. After performing a set of serial dilutions on 2 cm3 of the food, you inoculate corresponding agar plates with 0.1 ml of the appropriate diluent. The next day, you count 125 colonies on the nutrient agar plate from the 1 X 10-5 dilution tube. Likewise, you count 206 colonies (109 of which are pink) on a similarly inoculated MacConkey Agar plate from the 1 X 10-4 dilution. You inoculated each plate one-tenth (0.1) ml of sample from the tube. Based on this data, determine the following bacterial population densities (cfu/ml) that were in the original sample of this âburger:
⢠Gram-negative, lactose-fermenting bacilli: ______________ CFU/ml
⢠Non- Gram negative bacteria: _________________ CFU/ml
⢠Total bacteria: ____________ CFU/ml
You are to microbiologist for the Minnesota Department of Health. A sample of âsuspectâ ground beef from Jimboâs Grocery in Minneapolis is brought to your lab. After performing a set of serial dilutions on 2 cm3 of the food, you inoculate corresponding agar plates with 0.1 ml of the appropriate diluent. The next day, you count 125 colonies on the nutrient agar plate from the 1 X 10-5 dilution tube. Likewise, you count 206 colonies (109 of which are pink) on a similarly inoculated MacConkey Agar plate from the 1 X 10-4 dilution. You inoculated each plate one-tenth (0.1) ml of sample from the tube. Based on this data, determine the following bacterial population densities (cfu/ml) that were in the original sample of this âburger:
⢠Gram-negative, lactose-fermenting bacilli: ______________ CFU/ml
⢠Non- Gram negative bacteria: _________________ CFU/ml
⢠Total bacteria: ____________ CFU/ml
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FOR #4 A & B I don't know if I did it correctly.....Please check & the other questions I'm having a heard time on. Thanks!
A. You have been given a tube of E. coli. You are asked to make 1 mL total volume of 10-1 dilution of the bacterial culture. Explain how you would do this. Show all necessary calculations.
____ ml cells + _____ ml water = 1 ml (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 of diluent 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 of diluent must be added.
You have bacteria at a concentration of 5 x 108 CFU/mL. You spread 1 mL of this sample on an agar plate to obtain isolated colonies. How many colonies do you expect to find the next day after incubation at 370C? Can you count these colonies? Can you use this plate for determining concentration?
A. You have bacteria at a concentration of 1 x 103 CFU/mL (in real life â you donât know this, but we are just working on math skills here). You transfer 1 mL of this sample into 9 mL of water and then spread 1 mL on a plate of agar. How many colonies do you expect to find the next day after incubation at 370C? Can you count these colonies? Can you use this plate for determining concentration?
You take 0.05 mL of a culture of bacteria at a concentration of 4 x 107 CFU/mL, and add 4.95 mL of water to it. What is the dilution that you have performed? What is the concentration of bacteria (CFU/mL) in the diluted culture?
A. You have diluted a sample by 1000 fold (1/1000) and plated 1 mL on an agar plate. You observe 55 colonies. What was the concentration of the original sample in CFU/mL?
A. A bacterial sample has a concentration of 3 x107CFU/mL. You make serial dilutions of 10-3 followed by 10-2 and 10-1 dilutions. You finally plate 1 mL of the last dilution on an agar plate and incubate it at 370C. What is the total dilution? How many colonies do you expect to see on the plate?
Total dilution:
# of colonies expected on plate:
C. This time, you see 10 times fewer colonies than you had expected to see.What could have gone wrong? How will you fix this problem?
A bacterial sample has a concentration of 2 x106 CFU/mL. Show a scheme of dilutions to obtain 30-300 colonies on a plate. Your scheme should contain the volume of diluent (sterile water), volume of sample transferred each time, the concentration of bacteria (CFU/mL) in each dilution. You can assume you are plating 1 mL of the dilution on plates of nutrient agar. See Figure 1 in protocol.
These are the results of the experiment described in the protocol. From the data shown in the results section of Standard Plate Count protocol, calculate the concentration of bacteria (CFU/mL) in the original sample of E. coli. Show your calculations. Hint: remember that we donât use plates that have less than 30 or more than 300 colonies to do these calculations.
