Question

This

week you’ll count plaques on your phage titer plates to determine the original phage titer in

the tube we sampled from. Let’s say you counted 34 plaques on your clan’s “7” plate. Make a

table or diagram that shows how many phage particles were in each tube

of your dilution series.

Answer 1

Let us assume the following situation -

In tube 1, the orignial sample of phages was present. The concentration of this was x.

In tube 2, we added 1 ml of x and 9 ml of water to dilute it. This dilution is 10 fold dilution of tube 1. The concentration of this will be 1/10 of x or 0.1 x or 10^-1 x.

​​​​​​[dilution factor = final volume (9+1) / initial volume (1)]

In tube 3, we added 1 ml of 0.1 x and 9.9 ml of water. The dilution is 10 fold dilution of tube 2 or 100 fold of tube 1. The concentration of this will be 0.01 x or 10^-2 x.

Similarly, we can perform 10 fold dilution of each tube until the required dilution is reached (here, 10^-7 x is to be reached).

Tube 4 = 10^-3 x

Tube 5 = 10^-4 x

Tube 6 = 10^-5 x

Tube 7 = 10^-6 x

Tube 8 = 10^-7 x

Now it is given that the last tube, tube 8 contains 34 colonies. We know that it is 10 times diluted than tube 7, so tube 7 will contain 340 colonies.

Tube 7 contains 340 colonies and we know that it is 10 times diluted than tube 6, so tube 6 will have 3400 colonies.

Similarly,

Tube 5 will have 34000 colonies per ml.

Tube 4 will have 340000 colonies per ml.

Tube 3 will have 3400000 colonies per ml.

Tube 2 will have 34000000 colonies per ml.

Tube 1, the original sample contains 340000000 colonies per ml.

For better understanding, see diagram below -

Colonies are used in bacteria and titer is used in phages.

Please rate.