To determine whether bacterial cells are motile, they can be observed microscopically in a:

• A. fixed and heat-killed slide
• B. negative stain
• C. wet mount preparation
• D. Gram-stained smear

Answer: (C)

Verified step by step guidance

1. Understand the purpose of the test: To determine bacterial motility, you need to observe live bacteria moving under the microscope.
2. Evaluate each option: A fixed and heat-killed slide contains dead bacteria, so motility cannot be observed.
3. Consider the negative stain: This technique stains the background but does not keep bacteria alive or allow observation of movement.
4. Gram-stained smear involves fixing and staining bacteria, which kills them, so motility cannot be assessed.
5. Wet mount preparation involves placing a drop of liquid culture on a slide and covering it with a coverslip, allowing observation of live, motile bacteria in real time.