Bacterial smears are fixed before staining to:

• A. kill the bacteria and adhere them to the slide
• B. increase the thickness of the smear
• C. enhance the color intensity of the stain
• D. prevent the stain from binding to the cells

Answer: (A)

Verified step by step guidance

1. Understand the purpose of fixing a bacterial smear in microbiology: fixing is a preparatory step before staining that serves specific functions.
2. Recognize that fixing primarily serves to kill the bacteria, which is important for safety and to stop cellular processes that might alter the cells during staining.
3. Know that fixing also helps the bacterial cells adhere firmly to the microscope slide, preventing them from washing off during the staining and rinsing steps.
4. Consider the other options: increasing thickness, enhancing color intensity, or preventing stain binding are not the main purposes of fixing; these relate more to staining techniques or smear preparation.
5. Conclude that the correct reason for fixing is to kill the bacteria and adhere them to the slide, ensuring the sample remains intact and safe for microscopic examination.