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Plaque Assay Titration - (Nov/14/2013 )

In my experiment with bacteriophages, several dilutions gave me plaques between 30 and 300, so which dilution shall I use to calculate the phage titer?

Thank you very much.

-biology.student2013-

Any of them in theory - however, higher counts, if done correctly will be more accurate.

-bob1-

Thank you very much Bob1.

Do you mean the plate with higher counts of plaques or the plate with higher dilution?

-biology.student2013-

The plate with the higher count should (in principle) give a better statistical estimate of the phage abundance.

-phage434-

Yes, the higher count - if you think about it like this:  Say you have a plate with 30 plaques, and you find that you miscounted and there are actually 34 plaques - so your percent error is (30-34)/3*100 = 13%, but if you have a plate with 100 plaques, and it actually has 104 = 4% error...

-bob1-

Thank you very much Bob1 and Phage434 for your response.

 

Thanks a lot Bob1 for nicely explaining the statistical significance of choosing higher counts  

-biology.student2013-

Thank you very much Bob1 and Phage434 for your response.

 

Thanks a lot Bob1 for nicely explaining the statistical significance of choosing higher counts  

 

Yes, the higher count - if you think about it like this:  Say you have a plate with 30 plaques, and you find that you miscounted and there are actually 34 plaques - so your percent error is (30-34)/3*100 = 13%, but if you have a plate with 100 plaques, and it actually has 104 = 4% error...

 

Do keep 1 thing in mind:

 

the example bob1 gives is only good if you miscount 4.

 

The chances of miscounting more on a plate with more plaques is also bigger.....

Keep this in mind... because it can be important too!

This is statistics too...

 

I would not just use 1 dilution, but work with averages.

They should not vary too much if its the same settings of the experiment etc...

 

btw when you say: several dilutions gave me plaques between 30 and 300, I am assuming you mean that the end result was 30 up to 300 plaques for the same dilution?

-pito-

Yeah, I know.  The best way to do these things is with replicates. I'd typically do 3 plates for each dilution and average the counts.

-bob1-