Divide the number of plaques by the dilution factor , (ex. 10 – 6 for the most diluted sample) toobtain the number of Plaque Forming Units (PFU) in 100 μL of phage mixture.
What is meant by plaque forming units?
A measure of viable bacteriophage particles , determined by plating a known volume of a solution on to a bacterial lawn and subsequently counting the areas of bacterial lysis (plaques).
How is plaque assay calculated?
The titer of a virus stock can be calculated in plaque-forming units (PFU) per milliliter . To determine the virus titer, the plaques are counted. To minimize error, only plates containing between 10 and 100 plaques are counted, depending on the size of the cell culture plate that is used.
Is PFU the same as CFU?
403, “Analogous to the concept of a colony forming unit (CFU) in bacteriology. ... Note that, as is the case with CFU, the number of PFU reflects the number of phages able to form plaques in a sample, not the total number of virions.”
How do you calculate the number of plaque forming units?
To count, select a plate with between 30 and 300 plaques. Count the number of plaques, then multiply by 10, then multiply by the reciprocal of the dilution of that plate to give the number of plaque forming units per milliliter.
Why do we not use a TNTC or Tftc plaque assay plate?
Plates showing greater than 300 PFUs are too numerous to count (TNTC); plates showing fewer than 30 PFUs are too few to count (TFTC).
How many viruses are needed to form a plaque?
One virus is enough to form a plaque. So for one-hit kinetics, the number of plaques is directly proportional to the first power of the concentration of the virus inoculated.
What is a CFU count?
A colony forming unit, or CFU, is a unit commonly used to estimate the concentration of microorganisms in a test sample . The number of visible colonies (CFU) present on an agar plate can be multiplied by the dilution factor to provide a CFU/ml result.
What is PFU ratio?
Specific infectivity can be described as the number of viral particles present for every one particle that is able to infect a cell in culture. This is often represented as the ratio of particles per PFU; a lower ratio means that more of the viral particles yield plaques in the cell culture system tested (14, 15).
How is a plaque formed?
Plaque forms when bacteria in your mouth mix with sugary or starchy foods , such as milk, juice, soft drinks, bread, pasta and fruit. These bacteria release acids that break down carbohydrates in food and drinks.
How do you calculate Moi?
For figuring out the amount of virus you need to add for a certain MOI, use the formula: #cells * desired MOI= total PFU (or Plaque Forming Units
What is a high pfu mL?
A value of 1 means that every virus particle in the sample is able to form a plaque. For animal viruses, the particle-to-pfu ratio is often much higher, from 1 to 10,000 (the image shows values for different animal viruses – click to enlarge). These high values complicate the study of animal viruses.
Does a plaque forming unit necessarily equal a single infectious particle?
Theoretically, the plaque-forming unit includes only the infectious virus particles since a virus particle failing to infect a host cell will not be able to produce a plaque, hence, will not be counted. PFU rules out possible multiple-hit phenomena and include only the particles capable of infecting cells on their own.
What is the principle of plaque assay?
The plaque assay (Figure 2) is based on incorporation of host cells, preferentially in log-phase growth, into the medium . This creates a dense, turbid layer of bacteria able to sustain viral growth. An isolated phage can subsequently infect, replicate within, and lyse one cell.
What is the purpose of the plaque assay?
Plaque assays are used to count infectious particles . Samples are diluted and aliquots of each dilution are added to cultured cells. The cells are covered with an agaroseoverlay. Virus produced from an infected cell can infect nearby cells.
What is hard agar?
The hard agar is the substrate for bacterial growth . The soft agar is used to mix the bacteria and phage dilutions which is then spread over the hard agar.
