Microorganisms in their natural state, are colorless, and nearly invisible to the naked eye, even under a light microscope. To make them visible, the cell structures have to be contrasted from their environment by applying chromogenic dye or stains, and the technique is called staining.
Staining helps to differentiate various morphological types (by shape, size, arrangement, etc.), determine the staining characteristic of the organism, and demonstrate the purity of the culture. Staining also gives a presumptive idea for direct diagnosis of infections and aids in the study of various internal and external structures of microorganisms such as cytoplasmic membrane, nucleus, flagella, capsule, endospores, etc.
Slide-culture is a rapid method of preparing fungal colonies for examination and identification with little disturbance as possible.
Giemsa stain is a type of Romanowsky stain, primarily designed for the demonstration of malarial parasites in blood smears.
Reagents are primary stain (crystal violet), mordant (iodine), decolorizer (ethanol or acid-alcohol), and counterstain (safranin or dilute carbol-fuchsin).
The best way to visualize capsule is to stain the background using an acidic stain and to stain the cell itself using a basic stain.
Any basic dye such as methylene blue, safranin, or crystal violet can be used to color the bacterial cells. Not performed routinely in a diagnostic lab.
KOH preparation is used for the rapid detection of fungal elements in clinical specimens but it may not necessarily identify the species of the fungi.
QBC is based on acridine orange staining of centrifuged peripheral blood samples in a microhematocrit tube and examination under UV light.
Acridine orange is a dye that binds with the nucleic acid ( either DNA or RNA) present in organisms and fluoresce to emit various colors.
Albert stain is a type of differential stain used for staining metachromatic granules or volutin granules found in Corynebacterium diphtheriae.
In Schaeffer-Fulton`s method, primary stain-malachite green is forced into the spore by steaming the smear, safranin is counterstain.
Auramine-rhodamine fluorochrome staining also known as "Truant method of staining", is used to visualize Acid-fast bacilli (AFB).
Gram-positive bacteria retain the crystal violet-iodine complex and stain purple, whereas gram-negative bacteria stain pink.
Lactophenol cotton blue solution is a mounting medium and staining agent used in the preparation of slides for microscopic examination of fungi.
Bacteria are easier to detect in broth culture if the preparation is stained using toluidine blue rather than stained by the Gram staining technique.
Simple and useful wet-mount technique for staining bacterial flagella.
Ziehl-Neelsen acid fast stain is designed to stain bacterial cells containing long chain fatty (mycolid acids) such as Mycobacterium.
Based on the types and number of dyes used, staining can be categorized simple stain, negative stain, impregnation methods and differential stain.