please help answer the first paragraph (5 points) and the one after that (2 poin
ID: 209507 • Letter: P
Question
please help answer the first paragraph (5 points) and the one after that (2 points). The very last one which is also two points doesn't need to be answered.
PC, you perform a dilution series in order to figure out the original bacterial concentration of e puddle sa mple in order to compare it to your traditional SPC result. You perform the following dilution set: from your 1 L puddle s removed 450 L and added into another 8.5 x 103 L ofsterile water. Then you dilute this once again by taking 100 into 99000 of sterile water. You take a 10 mL sample of this and add it to 0.999 L. Your final odd-unit dilution nvolves 3.5 mL of the previous dilution into 67.5 mL of sterile water. You then plate out 120 onto an agar plate and incubate at room temperature overnight to find 278 colonies on the plate. What was the original microbial concentration of the puddle water sample? Based on your calculation, how many viable bacterial cells were present in your initial puddle sample? (Show your work for partial credit, hand written work is preferred over computer generated, 5 points) 2910 Up loo Finally, you decide to carry out an OD spectrophotometer reading from your sample. You find that your reading is 1.1 from the spectrophotometer. Given the following equation (y- 1.3274 x-1.045 x2+2.6232 x), what is the cell density given that Y represents cell density as the value x 10 cells/mL(this is identical to the table you worked from in lab)? What does this OD measurement represent in terms of your puddle sample? (Show your work for partial credit, hand written work is preferred over computer generated, 2 points) At the end of your puddle sample enumerating inquiry, you decide to meet your friend's downtown. They ask you your evening was thus far, at which point you decide to tell them about your puddle enumerating fiasco. if they are interested in knowing the overall bacterial count of your puddle sample, which of the above method results do you tell them about and WHY? (Typed answer worth 2 points)Explanation / Answer
First of all we will calculate the dilution factor in each of the serial dilutions-
1st dilution- 6ml into 84520micro.L of water or 6000 microL in 84520micro.L of water. Therefore the dilution factor can be calculated as (84520 +6000)/6000= 15.08 or 15 (we take the whole number only).
2nd dilutio-n 450 micro.L in 8.5 x 10-3 L or 450 micro.L in 8500micro.L. Therefore, dilution factor is equal to (8500+450)/450 = 20.
3rd dilution- 100 microL in 99000micro.L of water. The dilution factor in this case is equal to (99000+100)/100 = 1000
4th dilution- 10ml in 0.999L or 10ml in 999ml of water. Therefore, dilution factor can be calculated to be equal to (999+10)/10 = 100.
5th dilution- 3.5ml in 67.5ml. Hence the dilution factor = (67.5+3.5)/3.5 = 20.
Therefore, the total dilution factor, which is the product of all dilution factors = 15*20*1000*100*20 = 6 x 108 .
Now, CFU/ml = (no. of colonies x dilution factor) / volume of culture plate in ml = 278x 6x108)/(120 x10-3)
= 13.9 x 1011 CFU/ml. This is also the number of viable cells in your original sample.
To calculate Y, you will put x = 1.1 in the equation- y = 1.3274x3 -1.045x2+2.6232x,
Therefore, y = 1.3274(1.1)3 - 1.045(1.1)2 + 2.6232 (1.1), which gives y = 3.39.
Therefore, the cell density Y = y x 108 cells/ml = 3.39 x 108 cell/ml or 3.4 x 108 cells/ml
Hope this help. Thanks!
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