Question

you complete a gram stain on streptococcus bacteria and observe long chains of pink spheres. what could be the reason for this?
○ they are gram negative cocci.
○ you over decolorized the bacteria.
○ these bacillus bacteria must be contaminated.
○ you forgot to add counterstain to the slide.

question 10 (bonus) (1 point)
in a completed gram stain, gram-negative bacteria are colorless.
○ true
○ false

Explanation:

First Question (Gram Stain Observation)

• Option 1: Streptococcus is typically gram - positive (purple in Gram stain), so being gram - negative is incorrect.
• Option 2: Over - decolorization in Gram staining can remove the crystal violet - iodine complex from gram - positive bacteria, making them take up the counterstain (safranin) and appear pink, which matches the observation of pink spheres (cocci) in chains (Streptococcus is coccus - shaped and in chains).
• Option 3: Streptococcus is coccus, not bacillus, so this is incorrect.
• Option 4: If counterstain was forgotten, gram - negative bacteria would be colorless, but gram - positive would be purple. The observation is pink, so this is incorrect.

In a completed Gram stain, gram - negative bacteria take up the counterstain (safranin) and appear pink/red, not colorless. So the statement "In a completed Gram stain, gram - negative bacteria are colorless" is false.

Answer:

B. You over decolorized the bacteria.

Second Question (Gram - negative Bacteria Color in Gram Stain)