Answer:
The units used to measure the concentration of phage in a lysate are plaque-forming units per milliliter (pfu/ml)1. This is based on the number of clear spots or plaques that form on a bacterial lawn after the phage infects and kills the bacteria. A higher number of plaques indicates a higher concentration of phage in the lysate. Lysates with a final concentration greater than 10^9 pfu/ml are considered “High Titer” lysates.