Differential staining is a method used by laboratory analysts to distinguish between different cell types. It involves treating a sample with a series of dyes to impart colors to the cell, making the parts more visible under a microscope. This method is commonly used in bacterial identification, with the Gram stain being a useful first step. Animal cells can also be sorted using differential staining, with Wright’s stain being an example that can identify the types of blood cells present in a sample.
Although microbes or animal cells may be visible under a microscope, individual parts of the tiny cell can be difficult to differentiate as colors under a microscope may appear the same or the cell appears transparent. Laboratory analysts who specialize in the microscopic analysis of cells use staining methods to impart colors to the cell so they can see the parts clearly. Differential staining refers to the type of staining that allows the analyst to distinguish between different cell types; is a general term encompassing a variety of staining procedures.
When an animal is broken down into its cells, the cells can vary in appearance and function. Commonly different species have sets of cells that appear individual under a microscope. A common example of the difference between species and groups is how most bacteria can be divided into two groups based on their reaction to a particular type of stain called a Gram stain. Hans Christian Gram was a Danish microbiologist who first invented the stain in 1844, which is still in common use as a useful first step in bacterial identification in a laboratory setting.
In differential staining, a sample of a bacterial population is treated with a series of dyes in a process that includes steps such as heating and washing the samples so that the dye enters all cells. The various steps use dyes such as crystal violet and fuchsin, along with other substances such as alcohol and iodine to help set the color. Cells that appear pink are identified as Gram negative, while cells that are blue at the end of the process are Gram positive. This color difference helps the microbiologist pinpoint the cell wall type of the species, which helps narrow down the possible list of species to which an unknown sample belongs. In addition to indicating Gram type, the differential staining process makes the shapes and arrangements of the cells more apparent, which also aids in identification.
Animal cells can also be sorted under a microscope with differential staining. For example, cells circulating in the blood react differently to certain stains. One example is Wright’s stain, which incorporates dyes such as eosin and methylene blue, and which can tell a laboratory analyst what types of blood cells are present in a sample and at what concentration. For example, an eosinophilic cell tends to take in a lot of eosin staining compared to other blood cells. Analysts generally use the staining of the spots identified through differential staining along with other cellular characteristics such as size, shape, and internal structures to figure out which cells are present in a sample.
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