# Calculating Virus Titre

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1. Remove plates from incubator

2. Plaques formed should look like cleared out circles on the lawn

3. Each plaque is the result of one phage lysis one host bacterium, with the progeny from this lysis killing the surrounding bacteria

4. Determine which dilutions have about 70-300 plaques each

5. Count the number of plaques and write them down

a. Use the ipad ticker and a sharpie for fast counting

6. After counting, average the amount between replicates for each dilution

7. Take the number of plaques per plate and divide by the serial dilution number for that plate, then multiply according to volume added

a. For Example: 75 plaques on the 10^-5 plates, so divide 75 by 10^-5, giving you 7,500,000

8. This number represents the amount of virus in your original tubes per ml

a. We used 100 uL when plating, so multiplying the number above x10 gives us 1 mL

b. In the case of the example: 7.5 x 10^7 PFU / 1 mL