Staining Techniques

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.

Calcofluor White Staining: Principle, Procedure, and Application

Calcofluor White Staining: Principle, Procedure, and Application

Calcofluor white staining uses fluorescent dye, which especially stains the chitin present in the cell wall of fungi.

Periodic acid-Schiff (PAS) Staining: Principle, Procedure, and Application

Periodic acid-Schiff (PAS) Staining: Principle, Procedure, and Application

Periodic acid-Schiff (PAS) staining is a staining technique for demonstrating the carbohydrates and fungal cell wall components.

Slide Culture for Fungi: Principle, Procedure, Results

Slide Culture for Fungi: Principle, Procedure, Results

Slide-culture is a rapid method of preparing fungal colonies for examination and identification with little disturbance as possible.

Giemsa Stain: Principle, Procedure, Results

Giemsa Stain: Principle, Procedure, Results

Giemsa stain is a type of Romanowsky stain, primarily designed for the demonstration of malarial parasites in blood smears.

Preparation of Gram stain Reagents

Preparation of Gram stain Reagents

Reagents are primary stain (crystal violet), mordant (iodine), decolorizer (ethanol or acid-alcohol), and counterstain (safranin or dilute carbol-fuchsin).

Capsule Stain: Principle, Procedure, Results

Capsule Stain: Principle, Procedure, Results

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.

Simple Staining: Principle, Procedure, Uses

Simple Staining: Principle, Procedure, Uses

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 Mount: Principle, Procedure, Results, Uses  

KOH Mount: Principle, Procedure, Results, Uses  

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.

Quantitative Buffy Coat (QBC) Test

Quantitative Buffy Coat (QBC) Test

QBC is based on acridine orange staining of centrifuged peripheral blood samples in a microhematocrit tube and examination under UV light.

Acridine Orange Staining: Principle, Procedure, Results

Acridine Orange Staining: Principle, Procedure, Results

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: Principle, Procedure and Results

Albert Stain: Principle, Procedure and Results

Albert stain is a type of differential stain used for staining metachromatic granules or volutin granules found in Corynebacterium diphtheriae.

Endospore Staining: Principle, Procedure, Results

Endospore Staining: Principle, Procedure, Results

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

Auramine-Rhodamine Fluorochrome Staining

Auramine-rhodamine fluorochrome staining also known as "Truant method of staining", is used to visualize Acid-fast bacilli (AFB).

Gram Staining: Principle, Procedure, Results

Gram Staining: Principle, Procedure, Results

Gram-positive bacteria retain the crystal violet-iodine complex and stain purple, whereas gram-negative bacteria stain pink.

Lactophenol Cotton Blue (LPCB) Mounts

Lactophenol Cotton Blue (LPCB) Mounts

Lactophenol cotton blue solution is a mounting medium and staining agent used in the preparation of slides for microscopic examination of fungi.

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Toluidine Blue Staining in Microbiology: Procedure, Uses

Bacteria are easier to detect in broth culture if the preparation is stained using toluidine blue rather than stained by the Gram staining technique.

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Flagella Staining: Procedure, Results

Simple and useful wet-mount technique for staining bacterial flagella.

Ziehl-Neelsen Technique-AFB Staining

Ziehl-Neelsen Technique-AFB Staining

Ziehl-Neelsen acid fast stain is designed to stain bacterial cells containing long chain fatty (mycolid acids) such as Mycobacterium.

Types of Staining Techniques Used in Microbiology

Types of Staining Techniques Used in Microbiology

Based on the types and number of dyes used, staining can be categorized simple stain, negative stain, impregnation methods and differential stain.