What Is the Spread Plate Technique?

The spread plate technique is a method for transferring bacteria to an agar plate and distributing it evenly. The technique makes it easier to quantify bacteria in a solution.

In order to count the number of bacteria in a sample, scientists use a method that allows an even growth of bacterial colonies. The spread plate technique creates an even distribution of diluted bacteria on an agar plate.

The spread plate technique involves using a sterilized spreader with a smooth surface made of metal or glass to apply a small amount of bacteria suspended in a solution over a plate. The plate needs to be dry and at room temperature so that the agar can absorb the bacteria more readily, according to the American Society for Microbiology.

The scientist needs to distribute the bacteria immediately after applying it to the plate by positioning the spreader in a way that allows the bacteria to travel evenly after the application of an even pressure. Spinning the plate manually or using a turntable without allowing any pooling of the bacteria along the spreader offers a more even distribution. Alternatively, the scientist can rotate the spreader for the same effect.

After leaving the agar plate in a closed humidified container, bacterial colonies develop. The scientist can then quantify the growth of bacteria by inspecting the plate.