Gram stain, is a laboratory technique that is routinely used in microbiological studies of bacteria. It was designed by Christian Gram, a Danish scientist, in 1884. The goal was to get a Gram test that was possible to differentiate different groups of bacteria in order to study and classify them. The test was a success and soon became a very useful technique not only for the study of bacteria, but also to quickly identify an infection and select the most appropriate antibiotic to treat it.
The technique is based on applying a set of dyes to a sample of any origin (sputum, urine, pus, etc.) supposedly containing unidentified bacteria. The dyes stain the wall purple bacteria and after a few minutes, washing the dye is performed. After that the dye can remain in the bacterial cell wall or gone. In the first case the purple remain and would be Gram positive and, in the second wall would have a pink color, and would Gram negative.
These two groups of bacteria are the pillars on which the classification of the vast majority of bacteria is based. Each of the groups responds differently to each type of antibiotics so it is a useful technique to select the initial antimicrobial drug to an infection. Keep in mind that in certain situations (such as sepsis)It is very important to initiate appropriate antibiotic treatments early, so Gram stain is used in emergency situations on many occasions.
Gram stain also has certain limitations. Some bacteria have wall, such as the chlamydial, and can not be identified, like viruses. In those cases staining not color any germ. Another negative aspect of the test is that it can not identify the exact type of bacteria responsible for the infection. This requires performing a microbiological culture is always accompanied by an antibiogram to study accurately the most effective antibiotic.