auraminerhodamine

Auraminerhodamine, commonly referred to as auramine-rhodamine, is a fluorescent dye mixture used as a staining reagent in acid-fast staining to detect acid-fast organisms, particularly Mycobacterium tuberculosis, in clinical specimens. The stain typically combines auramine O and rhodamine B and is applied to prepared smears in microbiology laboratories.

The stain works by binding to lipid-rich components of the cell walls of acid-fast bacteria, such as mycolic acids. When exposed to blue or near-ultraviolet excitation light, the stained organisms fluoresce with bright yellow to orange colors against a dark background. This fluorescence makes a smear easier to screen rapidly under fluorescence microscopy compared with conventional bright-field stains.

Procedure and interpretation rely on a sequence commonly used in acid-fast testing: a smear is stained with the auramine-rhodamine solution, then decolorized with acid-alcohol, and briefly rinsed. The acid-fast organisms retain the fluorescent stain and appear as bright, filamentous or rod-shaped elements, while most background material does not fluoresce as strongly. A fluorescence-equipped microscope is necessary, and the method is valued for its sensitivity and rapid screening capability.

Advantages of the auramine-rhodamine technique include higher sensitivity for detecting mycobacteria in sputum and other specimens and the ability to scan slides quickly. Limitations include the potential for false positives from non-mycobacterial fluorophores or debris, photobleaching, and the need for appropriate fluorescence equipment and trained personnel. Proper safety handling and waste disposal are required due to the chemical nature of the dyes.