A plaque assay is performed beginning with 1 mL of a solution containing bacteriophages. This solution is serially diluted three times by combining 0.1 mL of each sequential dilution with 9.9 mL of liquid medium. Then 0.1 mL of the final dilution is plated in the plaque assay and yields 17 plaques. What is the initial density of bacteriophages in the original 1 mL?

Key Concepts

Bacteriophage Titer

Bacteriophage titer refers to the concentration of bacteriophages in a solution, typically expressed as plaque-forming units (PFU) per milliliter. It is determined by performing a plaque assay, where each plaque represents a single infectious bacteriophage that has lysed a bacterial cell. Understanding how to calculate titer is essential for quantifying viral populations in microbiological studies.

Serial Dilution

Serial dilution is a method used to reduce the concentration of a substance in a solution systematically. In this case, 0.1 mL of the original solution is mixed with 9.9 mL of liquid medium, creating a tenfold dilution. This process is repeated multiple times, allowing for the determination of the concentration of bacteriophages in the original sample by analyzing the resulting dilutions.

Plaque Assay

A plaque assay is a technique used to quantify the number of viral particles in a sample by measuring the number of plaques formed on a bacterial lawn. Each plaque corresponds to a single bacteriophage that has infected and lysed a bacterial cell. The number of plaques can be used to calculate the initial concentration of bacteriophages in the original sample, making it a crucial method in virology.