Your roommate regularly drinks straight from the milk bottle. One day you decide

Question

Your roommate regularly drinks straight from the milk bottle. One day you decide to analyze milk sample. You record that he opened new milk bottle at 8.00 am on Saturday morning, and drank 300 mL of milk. He was away for the rest of the weekend. No-one else drank from it. On Monday morning, you tale 10 mL of the sample to Micro lab for analysis. a) You record in the table how your prepared serial dilution. You plate 0.1 mL of sample #3 and 24 h later you count 250 cells. You calculate that the cell concentration in the milk sample on Monday morning was You read that the most common psychrophilic that can grow in dairy products have generation time of ~6 hours. If you make that assumption, you are able to infer that on Saturday morning your friend added__ cells into milk while drinking straight from the bottle.

Explanation / Answer

The explanation for the answer is given below:

1) The dilution for the three samples, for sample 1- it is 10-2, for sample 2- it is 10-1 and for sample 3- it is 2 * 10-1. The dilution factor which we will calculate is 1/dilution.

For Sample 1- we get 100 as dilution factor.

For sample 2- we get 10 as dilution factor.

For sample 3- we get 5 as dilution factor.

So, final dilution factor which we get is- 5000.

b) The sample is 0.1ml. After 24hours, the cell grown is 250.

Cell COncentration will be - sample/total volume of milk * no. of cells.

Cell concentration is= 0.1/5 * 250= 5 percent.

c) As there were 250 cells on monday morning when only 10ml of milk was brought to lab, now there was 300ml of milk drank and on saturday morning -

10ml- 250 cells

1ml - 25 cells

300ml- 300*25 cells= 7500cells

So, no of cells will be = 7500/100= 75 cells.

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