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In: Biology

The cell density of the original broth was ‘x’ bacteria/ml. After two serial 1:100 dilutions and...

The cell density of the original broth was ‘x’ bacteria/ml. After two serial 1:100 dilutions and two 1:10 dilutions, the final spread plate has 25 distinct colonies. Estimate the cell density ‘x’ of the original broth.

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Expert Solution

Ans:- The cell density in original culture can be determined by serially diluting the sample and then spread the diluted sample onto the LB agar plate, followed by incubation of plate for 14-16 hrs. You will see the colony onto the agar plate and count the number of colony. Once you have counted the colony multiply by dilution factor (means how many times you have diluted the original sample before spreading), you will get the number of colony /ml or bacteria/ml in original culture.

Step 1:- .Here, the original cell density is X bacteria /ml.

Step 2:- Two serial dilution of 1:100 = 1:100 * 1:100 = 1:10000 and two serial dilution of 1:10 = 1:10 * 1:10 = 1:100.

Step 3:- So, the total dilution factor is the multiplication of both the dilution factor = 1:10000 * 1:100 = 1:1000000. This means the original broth is diluted to 10-6.

Step 4:- The colony count is 25. So, the original cell density= colony count * dilution factor = 25 * 106 . = 2.5 *    107bacteria/ml.

Thus, the value of X = 2.5 * 107 . Thus, the original cell density is 2.5 * 107bacteria/ml or 25 * 106 bacteria/ml.

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