Which of the following best describes the Gram stain reaction of Bacillus cereus?

• A. Gram-positive
• B. Acid-fast
• C. Gram-negative
• D. Does not stain with Gram stain

Answer: (A)

Verified step by step guidance

1. Recall that the Gram stain is a differential staining technique used to classify bacteria based on the structure of their cell walls.
2. Understand that Gram-positive bacteria have a thick peptidoglycan layer in their cell walls, which retains the crystal violet-iodine complex, appearing purple under the microscope.
3. Recognize that Bacillus cereus is a rod-shaped bacterium known to have a thick peptidoglycan layer characteristic of Gram-positive bacteria.
4. Eliminate options that do not fit Bacillus cereus characteristics: Acid-fast bacteria have a waxy cell wall and require a different staining method, Gram-negative bacteria have a thin peptidoglycan layer and do not retain the crystal violet stain, and 'Does not stain with Gram stain' is incorrect because Bacillus cereus does stain.
5. Conclude that the best description of the Gram stain reaction of Bacillus cereus is Gram-positive.