KVV E-Modules

1. Determining Bacteriophage Titer

1. Determining Bacteriophage Titer

Bacteriophages (phage) are obligate intracellular parasites. They multiply inside a bacterium by making use of some or all of the host (ie., bacteria) biosynthetic machinery (viruses that infect bacteria are known as bacteriophage). They enter the bacterial cell by ‘landing’ on the cell wall and injecting their DNA into the bacterial cytoplasm. After entry, the phage DNA acts as a template for production of phage proteins. These proteins replicate the phage and subjugate the cell, eventually causing lysis and death of the host cell. A bacteriophage particle is even harder to see than a bacterium. Viruses are beyond the limits of resolution of the light microscope and can be seen only with electron microscopes. Fortunately, we can use a technique very similar to the colony-counting technique used to measure the number of bacteria to count phage particles, known as the plaque assay. Lytic phages are enumerated by this method.