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.

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

Thank you very much Bob1.

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

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

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...

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 on Sun Nov 17 21:01:24 2013 said:

Thank you very much Bob1 and Phage434 for your response.

 

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

bob1 on Sat Nov 16 20:43:36 2013 said:

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?

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.