introduction to Gram’s stain is post where we will have quick introduction to what is stain , what is dye , what it’s actually process to make it and all the things .
Let’s have a quick intro
A simple stain such as loffler’s is of great value for many purposes.but another staining procedure, devised by danish scholar christian gram in 1884, is more valuable because it enables us to differentiate between kinds of bacteria that are morphologically indistinguishable yet of different species. It is therefore called differential stain.
To the smear which , for purpose of discussion, we shall assume to contain a variety of bacteria, crystal violet solution is applied for 30 seconds. This is gently rinsed off and an iodine solution is applied for 30 seconds. This , in turn , is rinsed off. All of the cell are deeply stained. 95% ethyl alcohol is applied and renewed until all but the thickest parts of smear have ceased to give off dye. This usually takes from 20 seconds to one minute. The differential feature of the method is now apparent . examination with the microscope will reveal the fact that as gram found while many bacteria resin the violet-iodine combination , others will have yielded it largely to the alcohol and are almost as nearly invisible as before. Those species of bacteria which retain the stain are gram positive and those which yield it to the alcohol are called gram negative.
But the staining process is not yet complete. There is still the important final step of applying the counterstain- a dye of some contrasting colors usually eosine(red), saffranine(red), brilliant green or bismarck brown. Any one of therese dyes colors the gram-negative species; they become as visible as the gram-positive ones but are readily differentiated by their color.
Thus, by applying gram’s stain, which takes but five to six minutes, one can learn a great deal about any bacterium. We make visible not only form, size and certain other structural details, but we can at once assign the organisms to one of the great artificial groups of bacteria.
1)Gram positive bacteria
2) Gram negative bacteria
Some organisms are “borderline” case, in respect to gram’s stain, sometimes being positive, other times negative. And sometimes both positive and negative cells of the same organism are seen in the same culture.