Which statement about the acridine orange stain is not true?

• A. Binds to the teichoic acid of the cell wall
• B. Requires the use of a fluorescence microscope
• C. Is more sensitive than the Gram stain
• D. Is recommended for fluid and exudates with low bacterial concentrations

Answer: (A)

Acridine orange is a fluorescent stain that detects bacteria by binding to nucleic acids (DNA and RNA), not by sticking to cell wall components. This dye is excited by UV or blue light and viewed under a fluorescence microscope, where the stained bacteria stand out clearly against the background. Because fluorescence enhances contrast, acridine orange can reveal bacteria at lower concentrations than the Gram stain, making it more sensitive in many rapid-detection scenarios. It’s particularly useful for fluids and exudates where bacterial numbers are low, providing quicker, more visible results.

The statement about binding to teichoic acid is not true because acridine orange’s mechanism is nucleic-acid binding, not specific interaction with teichoic acids in the cell wall. This is why it doesn’t target a particular cell-wall component; instead, it highlights bacterial presence by staining their genetic material. The other points—requiring a fluorescence microscope, generally being more sensitive than Gram staining, and being useful for specimens with low bacterial concentrations—are all consistent with how acridine orange is used in practice.