Which tissue serves as the control slide for Brown & Brenn Gram stain?

• A. Infected tissue
• B. Grey matter
• C. Spleen or liver
• D. Aorta or skin

Answer: (A)

The main idea here is using a proper control to verify the staining procedure when staining tissue sections for bacteria with the Brown & Brenn Gram stain. A positive control must have actual bacteria so you can confirm that the staining steps—crystal violet uptake, iodine mordanting, decolorization, and counterstaining—are working correctly. An infected tissue provides visible bacteria, allowing you to see the expected Gram-positive organisms staining purple and Gram-negative organisms staining pink after counterstaining, which confirms the procedure produced reliable results.

Using tissue like grey matter, spleen or liver, or aorta or skin as a control is less reliable because these tissues may be sterile or might not consistently contain bacteria in the expected forms. They wouldn’t reliably demonstrate that the stain and decolorization steps are functioning, which is why an infected tissue is the best choice for a control slide.