Which control slide is used for Brown & Brenn Gram staining?

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

Answer: (A)

Brown & Brenn Gram staining is used to visualize bacteria within tissue sections, so a control slide must show bacteria present. An infected tissue section provides bacteria that should take up the Gram stain and appear with the expected colors, confirming that dye penetration, decolorization, and counterstaining are working properly. In contrast, non-infected tissues such as grey matter, spleen or liver, or aorta or skin wouldn’t demonstrate bacteria and wouldn’t verify the staining procedure, making them unsuitable as a positive control. So, the infected tissue slide is the best control.