Canadian Society for Medical Laboratory Science (CSMLS) Practice Exam

What is the purpose of fixing a bacterial smear?

1. Remove crystal violet stain repost

2. Adhere samples to the slide

3. Destroy all organisms

4. Remove excess protein

The correct answer is: Adhere samples to the slide

Fixing a bacterial smear primarily serves to adhere samples to the slide, which is crucial for the subsequent staining and analysis processes. When a bacterial smear is prepared, the organisms are suspended in a liquid medium and spread over the surface of a microscope slide. The fixation process, often involving heat or chemical agents like methanol or formaldehyde, effectively secures these bacteria to the slide, preventing them from washing away during the staining and rinsing processes. This adherence is important because it ensures that the cells remain in place while the slide is being processed and viewed under the microscope. Without this fixation step, it would be challenging to obtain accurate and reliable microscopic observations, as the bacteria might detach during handling. The other processes listed do not accurately describe the main purpose of fixation. For example, while some agents used to fix the smear may have mild effects on proteins, the primary goal is not to remove excess protein. Similarly, fixation does not destroy all organisms; instead, it preserves their structure and morphology for easier examination. Lastly, the fixation process does not involve removing the crystal violet stain; rather, it prepares the cells to be stained effectively by stabilizing them on the slide.