Question

The way we measure phages is by observing how many cells it is able to lyse (counting plaques). Same dilution principle as the one used for bacteria. A _______ occurs wherever a single virus initially infected one bacterium in the culture.

Answer 1

Plaques on a bacterial lawn represent individual bacteriophages that have infected and lysed bacterial cells. Counting plaques can determine the concentration of viruses in a lysate. A plaque results from the viral lytic cycle, indicating the progeny of a single infecting virus particle.

Step-by-step explanation:

The process being described is the method of quantifying the number of bacteriophages, which are viruses that infect bacteria. The clearings observed on a bacterial lawn after inoculation with phages are known as plaques. Each plaque corresponds to a single virus particle that initially infected a bacterium and then caused a cascade of infections leading to the lysis of surrounding cells. This forms a visible clearing or plaque representing progeny of the original infecting virus particle.

The example provided illustrates that if 500 plaques are counted on an agar plate, it indicates there were 500 infective virus particles in the volume of lysate applied. The number of plaques can be used to calculate the viral concentration in the original sample before dilution. Given that this sample was the fourth in a series of 10-fold dilutions, the original lysate contained 2,000 phage particles in the same volume (10 µl).