Phage Discovery Guide: Serial Dilution Protocol

For POLS Labs

The number of infectious bacteriophages in your stocks may seem absurdly high.  For example, for some experiments, we may expect there to be 1-100 billion (1e9 to 1e11) phage per milliliter of your stock.  To be able to “count” the number of infectious bacteriophages are in your sample, you will need to dilute your sample an absurd amount.

In this video, you will see that the method to achieve such diluted sample is through serially (time after time) diluting your sample a reasonable amount.  The steps are:

1. Dilute 1 part sample into 9 parts water, then…     (*label this tube 1e-1 or 10^-1)
2. Dilute 1 part of that diluted sample into 9 parts water, then…   (*label this tube 1e-2)
3. Dilute 1 part of that diluted sample into 9 parts water, then…   (*label this tube 1e-3)
4. Dilute 1 part of that diluted sample into 9 parts water, then…   (*label this tube 1e-4)
5. Dilute 1 part of that diluted sample into 9 parts water, then…   (*label this tube 1e-5)
6. Dilute 1 part of that diluted sample into 9 parts water, then…   (*label this tube 1e-6)
7. Dilute 1 part of that diluted sample into 9 parts water, then…   (*label this tube 1e-7)
8. Dilute 1 part of that diluted sample into 9 parts water, then…   (*label this tube 1e-8)
9. Stop at some logical point

The serially-diluted bacteriophage can then be used in a spot titer or full plate protocol.  The spot titer is a variation of the spot test protocol where you will use some (or all) of your serially-diluted samples to “spot” your top agar.