Which stain is known for its dark blue coloration when staining Helicobacter?

Toluidine blue is a metachromatic dye that is often used to highlight certain cellular components and structures in histological preparations. When staining Helicobacter, especially Helicobacter pylori, this stain is recognized for producing a distinct dark blue coloration. The metachromatic properties of toluidine blue allow it to bind to different tissue components, resulting in varied shades when applied to various cells. This is particularly advantageous for visualizing the presence of Helicobacter in gastric tissues, as the bacteria can be easily seen against the background of surrounding tissues.

Other staining techniques mentioned, like the Masson-Fontana technique, are generally used for different purposes, such as staining for melanin or demonstrating reticular fibers. Giemsa stain is primarily utilized in blood smears and cytological specimens to identify parasites and to provide information about cell morphology, while Wade-Fite stain is better suited for demonstrating microorganisms in specific types of tissue or infections. Thus, toluidine blue stands out due to its specific application and the clarity of the coloration it provides for Helicobacter species.