Answer
See the explanation below
Work Step by Step
She left the crystal violet on the slide far too long (a whole week).
Why this ruins the stain
Crystal violet is the primary stain in a Gram stain.
If it stays on too long, the bacteria will all look dark purple, even the ones that should NOT be purple.
This means she won’t be able to tell if the bacteria are Gram-positive or Gram-negative
Would she get good results using last week’s bacterial culture?
No, she would not get good, reliable results.
Why not?
Old cultures (older than 24 hours) start to die or weaken.
Gram-positive bacteria lose their ability to hold the crystal violet stain.
They may look pink like Gram-negative bacteria, even if they are actually Gram-positive.
This gives a false Gram reaction.
