Because of a snowstorm, your regular laboratory session was cancelled and the gram staining procedure performed on cultures incubated for a longer period of time. Examination of the stained B. cereus slides revealed a great deal of color variability, ranging from an intense blue to shades of pink. Account for this result.

Bacteria start to die, thereby changing the dye concentration in the medium and producing different colors

Explanation:

Bacillus cereus are Gram-positive, rod-shaped bacteria that form orange-pink colonies in agar media (e.g., BACARA medium, which is used for detection and enumeration of B. cereus). In this case, it is expected that after a long time without taking care of the culture, the bacteria started to die. Subsequently, lysed bacterial cells lost their dye which accumulated in some areas of the medium, thereby showing different colors ranging from an intense blue (areas with dead bacteria) to shades of pink (areas with bacteria still alive and viable).

did you fail the test? xd