When performing a Gram stain on Bacillus megaterium, what staining result is expected under the microscope?

• A. Gram-positive purple cocci in clusters
• B. Acid-fast red rods after decolorization with acid-alcohol
• C. Gram-positive purple rods
• D. Gram-negative pink rods

Answer: (C)

Verified step by step guidance

1. Recall the characteristics of Bacillus megaterium: it is a Gram-positive bacterium and has a rod (bacillus) shape.
2. Understand the principle of Gram staining: Gram-positive bacteria retain the crystal violet stain and appear purple under the microscope, while Gram-negative bacteria do not retain it and appear pink after counterstaining.
3. Identify the shape and arrangement: Bacillus megaterium is rod-shaped, not cocci (spherical) or arranged in clusters like staphylococci.
4. Eliminate options that describe acid-fast staining results, as Bacillus megaterium is not acid-fast and will not appear red after acid-alcohol decolorization.
5. Conclude that the expected result after Gram staining Bacillus megaterium is purple rods, indicating Gram-positive rods under the microscope.