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Plaque Assay Titration

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#1 biology.student2013

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Posted 14 November 2013 - 01:27 PM

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.

#2 bob1

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Posted 14 November 2013 - 02:27 PM

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

#3 biology.student2013

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Posted 16 November 2013 - 01:45 AM

Thank you very much Bob1.

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

#4 phage434

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Posted 16 November 2013 - 06:10 AM

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

#5 bob1

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Posted 16 November 2013 - 12:43 PM

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...

#6 biology.student2013

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Posted 17 November 2013 - 01:01 PM

Thank you very much Bob1 and Phage434 for your response.

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

#7 pito

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Posted 29 November 2013 - 02:33 PM

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?

If you don't know it, then ask it! Better to ask and look foolish to some than not ask and stay stupid.

#8 bob1

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Posted 29 November 2013 - 02:36 PM

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.