GRAM stain


Gram stain or also known as Gram stain is the name given to a type of differential stain that is used in the area of ​​bacteriology to visualize bacteria, especially in clinical samples. The name of this coloration is due to the Danish bacteriologist Christian Gram, who was responsible for developing the technique in 1884. Gram’s main objective was to obtain a test that would allow him to differentiate various groups of bacteria so that he could study them and develop a classification of them. Gran’s experiments turned out to be a complete success and it would quickly establish itself as one of the main techniques used to study bacteria, since it allowed them to be identified quickly and effectively in an infection and select the most appropriate antibiotic. to treat this infection.

The procedure to perform a staining is as follows: the first thing is to take the sample of bacteria that is to be colored, then with a swab it must be spread on a slide and then it must be allowed to dry at room temperature or, failing that, use a lighter, taking special care not to burn the bacteria. After that, the sample must be fixed on the slide using methanol for approximately 1 minute.

Subsequently, the gentian violet dye is placed on the slide and allowed to stand for 1 minute. It is important to note that this dye has the ability to pass through any type of bacterial wall and that is why it can stain both Gram-positive and negative bacteria. After that, the sample should be rinsed with water and then Lugol added, so that said substance covers the entire sample and waited for one minute. Lugol is a compound that is largely made up of iodine, which in this case is responsible for fixing the gentian violet dye to the sample.

After the steps described above, the slide must be washed with a mixture of alcohol and acetone for a period of approximately 30 days, it is in this step, when the Gram stain really ends, this is because the mixture of alcohol and acetone is responsible for dissolving the lugol and gentian violet complexes.