Question

One of your lab partners has followed the recommended procedure of running Gram-positive and Gram-negative control organisms on her Gram stain of unknown species. Her choices of controls were E. coli and B. subtilis. She tries several times and each time concludes she is decolorizing too long because both controls have pink cells (one more than the other). What might you suggest she try and why?

Answer 1

Answer:

The correct answer is "I would suggest her to change the Gram positive control from Bacillus subtilis to other bacteria".

Explanation:

Bacillus subtilis, and the species from the genre Bacillus, are known for losing the crystal violet coloration during Gram testing. It is likely that B. subtilis might look pink under the procedure for this reason. I would suggest to change her Gram positive control from B. subtilis to other bacteria. For instance, she could try with Staphylococcus aureus, a widely used bacteria as Gram positive control.