Acid-fast stain

Acid-Fast Stain

The acid-fast stain is a type of laboratory staining technique used to detect a type of bacteria known as acid-fast bacilli. Acid-fast organisms are characterized by their high degree of resistance to decolorization by acids and alkalis. This makes the acid-fast stain useful for visualizing and identifying members of the mycobacterium family, such as Mycobacterium tuberculosis, which is the most common cause of tuberculosis.

Preparation

The acid-fast stain is usually performed on samples of sputum, bronchial secretions, and respiratory tissue. The sample can be prepared with a standard fixative such as ethanol or acetone.

Procedure

The acid-fast stain involves four main steps:

• Applying the first stain: Crystal violet is used to make the cell walls of the acid-fast organisms crystal violet in color.
• Destaining with acid-alcohol: This step uses an acid-alcohol solution to remove the crystal violet color from non-acid-fast organisms.
• Applying the second stain: The cells are then treated with the counterstain malachite green.
• Destaining with acid-alcohol: This step uses an acid-alcohol solution to remove the malachite green color from all bacteria.

Types

There are two main types of acid-fast stain:

• Ziehl-Neelsen (ZN) stain: This is the most commonly used acid-fast stain and is used to detect members of the mycobacterium family.
• Kinyoun stain (also known as the modified ZN stain): This acid-fast stain is more sensitive than the ZN stain and is often used to detect other types of acid-fast bacilli.

Risks

Acid-fast stains are generally considered to be safe for use in the laboratory. However, the acid-alcohol solutions used to prepare samples and destain cells can be irritating to the skin and eyes, so appropriate protective clothing and eye protection should be worn.

Why Should We Use Acid-fast Stain?

Acid-fast stains are used to identify and visualize the presence of acid-fast bacteria such as Mycobacterium tuberculosis, which are important causes of disease in humans. The acid-fast stain can also be used to differentiate between species of acid-fast bacilli.

When to Use Acid-Fast Stain?

The acid-fast stain is usually used to diagnose tuberculosis and other Mycobacterium infections. It can also be used to diagnose other diseases caused by acid-fast bacilli, such as leprosy or brucellosis.