I'm reading a protocol for phage display. It says to isolate the phages, then prepare a phage dilution series from 10-4 to 10-13 cfu, then use these dilutions to infect E. coli and count the cfu to determine the phage library titer. But how can I prepare a specific cfu dilution series before I count the cfu?
I guess that what they mean is that you should prepare 10-fold dilutions starting with 10-4 until 10-13. They are probably not talking about the amount of cfu, but about dilution factors.
In my hands, typical purified phage preps are about 10 13 cfu/ml. If you also know the concentartions you usually get (after titration, of course), you can decide whether this dilution range is appropriate in your case or not.
To further simplify.... Add 990 ul dilution solution (LB media) with your 10 ul phage that gives you 10^3 dilution and dilute serially to 10^5 10^7 etc. Finally you can determine the titer of your phage by plaque assays. If you see too many colonies (Phage lysis or blue colonies incase of IPTG/x-gal) dilute further to get the cfu/ml phage.
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