How is a smear for an acid-fast stain fixed?

In the context of preparing a smear for an acid-fast stain, fixing the smear to the slide is an essential step that ensures the cells adhere properly and can be stained effectively. The correct method for fixing a smear for an acid-fast stain involves using a slide warmer at 65 degrees Celsius for a specified period, typically around 2 hours. This controlled heat ensures that the bacteria are adequately killed and fixed to the slide without causing damage that could lead to loss of structural integrity.

The application of heat also assists in the penetration of the stain, particularly in the case of acid-fast organisms like Mycobacterium species, which have waxy cell walls that resist typical staining methods. By using heat fixation, the phospholipid bilayer is altered in a way that enhances dye retention, making it crucial for successful acid-fast staining.

In this context, the other options would not provide the same effective fixation method. For example, methyl alcohol is typically used in different staining protocols but does not involve the necessary heat treatment required for acid-fast stains. Acid-alcohol is more commonly used as a decolorizing agent in the staining process after fixation, and Tergitol No. 7 is a surfactant useful in certain contexts but not applicable for the fixation