Final answer:
After the Ziehl-Neelsen staining, acid-fast bacteria appear red or pink because they retain the primary stain carbol fuchsin, while non-acid fast bacteria are counterstained and appear blue.
Step-by-step explanation:
The Ziehl-Neelsen procedure is a powerful staining technique that highlights the distinct structural features of acid-fast bacteria, particularly those belonging to the genus Mycobacterium. The key characteristic of acid-fast bacteria is the presence of waxy mycolic acids in their cell walls, rendering them resistant to conventional staining methods.
During the Ziehl-Neelsen procedure, acid-fast bacteria exhibit a remarkable resistance to decolorization. The initial step involves staining with carbol fuchsin, a red-colored primary stain. Acid-fast bacteria retain this stain even after exposure to a decolorizer, often an acid-alcohol solution. This resistance is attributed to the impermeability of the waxy cell wall to the decolorizing agent. As a result, acid-fast bacteria maintain their red or pink appearance, creating a sharp contrast against the background.
Conversely, non-acid fast bacteria lack the waxy cell wall structure and readily lose the primary stain during decolorization. Subsequently, these bacteria are counterstained with methylene blue, imparting a blue coloration to the cells. This differential staining approach allows for a clear differentiation between acid-fast and non-acid fast bacteria based on their coloration.
The Ziehl-Neelsen staining technique is particularly valuable in the identification of acid-fast pathogens, such as Mycobacterium tuberculosis, the causative agent of tuberculosis. The distinctive color contrast facilitates the detection of acid-fast bacilli in clinical samples, aiding in the diagnosis of diseases caused by these bacteria. Overall, the Ziehl-Neelsen procedure is an essential tool in microbiology, contributing to the accurate identification of specific bacterial species with unique cell wall characteristics.