Name DATA SHEET Date Lab Section 6-1 continued) I was present and performed this
ID: 132208 • Letter: N
Question
Name DATA SHEET Date Lab Section 6-1 continued) I was present and performed this exercise finitials) 23 You are told that a sample has betueen 2.5 × 10' and 2.5 × 10s cells/mL. Devise a complete but efficient (that is, no extra plates!) dilution scheme that will ensure getting a countable plate. 24 A sample has between 3.3 x 10" and 3.3 x 10 CFU/ml. Devise a complete but efficient (that is, no extra plates!) dilution scheme that will ensure getting a countable plate. Two plates recette d 100? L rom the same dilution tube. The irst plate had 293 colonies, whereas the second had 158 colonies. Suggest reasonable sources of error 26 Two parail disation series were made from the same original sample. The plates with sample volumes of 10- mL from each dilution series yielded 144 and 93 colonies. Suggest reasonable sources of errorExplanation / Answer
The range for countable CFU is from 30-300 colonies and this also provides statistical accuracy.
23) If the no of cell/mL is between 2.5X103 to 2.5X105 then the dilution scheme that will ensure countable CFU will be as follows: We will take 0.1 mL of the cell and will mix with 0.9 mL of setrile saline solution, the total volume will be 1.0 mL and it will be represented as 10-1 dilution. From 10-1 dilution 0.1 mL will be taken and mix with 0.9 mL of setrile saline solution, the total volume will be 1.0 mL and it will be represented as 10-2 dilution. Like wise 10-3 and dilutions will be prepared. The expected number of cells/mL in 10-1 will range from around 2.5X102-2.5X104 , in 10-2 will range from around 25-2.5X103 cells/mL whereas in 10-3 will range from around 2.5-2.5X102 cells/mL. Thus we can 0.1 mL of pick 10-2 and 10-3 dilutions and spread on growth media plate and incubate at desired tempreture and for required time period. This will result in countable CFU.
24) Refer the above solution for understanding the concept
If the no of cell/mL is between 3.3X104 to 3.3X106 then the dilution scheme that will ensure countable CFU will be as follows: We will prepare dilutions upto 10-4 . The expected number of cells/mL in 10-1 will range from around 3.3X103-3.3X105 , in 10-2 will range from around 3.3X102-3.3X104 cells/mL, in 10-3 will range from around 33-3.3X103 cells/mL whereas in 10-4 will range from around 3.3-3.3X102 cells/mL. Thus we can 0.1 mL of pick 10-3 and 10-4 dilutions and spread on growth media plate and incubate at desired tempreture and for required time period. This will result in countable CFU.
25) The error might have arised due to use of Hot Spreader that had killed inoculum in one othe dilution resulting in growth of less number of colonies in the plate. Or else the dilution is not prepared correctly due to which CFU count is varying.
26) The error might have arised due to improper spreading of inoculum on the media plate and because of which resulted in poor saperation of colonies. Overlapping colonies or mat formation in areas might have resulted in difference in CFU count
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