An example of a negative stain is?

A negative stain is a method used to visualize bacteria by staining the background rather than the cells themselves. This technique allows for the observation of cell morphology and size because the cells remain clear against a colored background. The India ink stain is a classic example of a negative stain; it effectively provides contrast by darkening the background, making encapsulated organisms, like Cryptococcus neoformans, stand out.

In contrast, the other stains mentioned do not qualify as negative stains. For instance, the auramine-rhodamine stain is primarily used for the detection of mycobacteria and stains the organisms themselves rather than the background. The Gram stain is a fundamental bacteriological technique that distinguishes bacteria based on their cell wall composition by staining the cells. Methylene blue, on the other hand, is a basic stain that directly colors the bacterial cells, making them the focus of visualization rather than the background.