Acid-fast

Acid-fast

The term "acid-fast" refers to a characteristic of certain bacteria and other microorganisms that makes them resistant to decolorization by acids during staining procedures. This property is primarily used in the identification and classification of bacteria, particularly in the diagnosis of diseases such as tuberculosis.

Overview

Acid-fastness is a physical property of certain bacterial cell walls that makes them resistant to decolorization by acids during staining. This property is due to the high lipid content in the cell wall, particularly the presence of mycolic acids. The most well-known acid-fast bacteria are members of the genus Mycobacterium, which includes the pathogens Mycobacterium tuberculosis and Mycobacterium leprae.

Staining Techniques

The most common staining technique used to identify acid-fast bacteria is the Ziehl-Neelsen stain. This method involves the following steps:

1. Primary Stain: The bacteria are stained with carbol fuchsin, a red dye. 2. Decolorization: The slide is then treated with an acid-alcohol solution. Non-acid-fast bacteria will lose the red stain, while acid-fast bacteria retain it. 3. Counterstain: A counterstain, such as methylene blue, is applied. Non-acid-fast bacteria will take up the blue stain, while acid-fast bacteria remain red.

Another method is the Kinyoun stain, which is a cold staining method that does not require heating.

Clinical Significance

Acid-fast bacteria are significant in clinical microbiology due to their role in infectious diseases. Mycobacterium tuberculosis, the causative agent of tuberculosis, is the most notable acid-fast bacterium. The ability to identify acid-fast bacteria quickly and accurately is crucial for the diagnosis and treatment of tuberculosis and other mycobacterial infections.

Other Acid-fast Organisms

While Mycobacterium species are the most well-known acid-fast organisms, other genera such as Nocardia and Cryptosporidium also exhibit acid-fastness. These organisms can cause opportunistic infections, particularly in immunocompromised individuals.

Also see

• Gram stain
• Bacterial cell wall
• Mycobacterium
• Tuberculosis
• Ziehl-Neelsen stain