Refer to the figure (right) for questions 1-3. Determine the concentration or di
ID: 278092 • Letter: R
Question
Refer to the figure (right) for questions 1-3. Determine the concentration or dilution factor for the flasks and plates. From the original culture I mL of broth was transferred to Flask A which contains 99 mL CULTURE of sterile water. Then I mL from Flask A is transferred to Flask B and then I mL from Flask B is transferred to Flask C. 1 ml 99 ml 99 ml 99 ml Give the dilution of: Flask A Flask B lask C Plate A Plate B Plate C 0.1 ml 0.1 ml I. What is the dilution from the original to Flask A? If 17 colonies grew on plate A, how many 1.0 ml 1.0 ml Colony Forming Units (CFU) were in the 2. What is the dilution from Flask A to Flask B? What is the dilution from the original to Flask B? What is 3. What is the dilution from the original to Flask C? If 133 colonies grew on plate C how many CFU were 4. Asa ple was diluted by placing a 0.1mL aliquot into 0.9 mL of diluent, and 10? L of this dilution was 5. original? the dilution from Flask B to Flask C in the original? pour-plated. After incubation, 253 colonies appeared. What is the CFU/mL in the original specimen? A serial dilution was prepared by adding 0.1 mL to 9.9 mL, and 0.I of that to 9.9 mL of fresh diluent. Then, 0.I mL of the last dilution was spread. Later, 76 colonies were counted. What was the original CFU/mLExplanation / Answer
1. Tube 1: Undiluted sample
Tube 2: Dilution 1 = 1 mL of undiluted sample + 99 mL diluent: Dilution factor = 10^-2
If 17 colonies appeared on plate A,
CFU of the original undiluted sample = 1700 CFU/mL
2. Tube 3: Dilution 2 = 1 mL of dilution 1 + 99 mL diluent: Dilution factor = 10^-2
Original dilution (From undiluted sample to B) = 10^-2 X 10^-2 = 10^-4
3. Tube 4: Dilution 3 = 1 mL of dilution 2 + 99 mL diluent: Dilution factor = 10^-2
Original dilution (From undiluted sample to C) = 10^-4 X 10^-2 = 10^-6
If 33 colonies appeared on plate C,
CFU of the original undiluted sample = 33 X 10^6 CFU/mL
4. Dilution = 0.1 mL in 0.9 mL = 10^-1
Number of colonies appeared = 253/100 uL = 2530/mL
CFU of the original undiluted sample = 2.53 X 10^4 CFU/mL
5.
Dilution 1 = 0.1 mL + 9.9 mL = 10^-2
Dilution 2 = 0.1 mL + 9.9 mL = 10^-2
Observed CFU = 76 CFU/0.1 mL = 760 CFU/mL
CFU of the original undiluted sample = 7.6 X 10^6 CFU/mL