BIOLOGY Volume 2 - A Guide to General Biology - 2004

12. MICROBIOLOGY AND BIOTECHNOLOGY

12.7. Stained Bacteria — Gram Staining

Although living Bacteria can be observed using a phase-contrast Microscope, they are more commonly fixed and stained beforehand.

One of the staining techniques that helps identify bacteria is Gram staining. This method was first developed by the Danish physician Hans Christian Gram in 1884. Before staining, all bacteria are colorless; after staining, Gram-positive bacteria appear purple, while Gram-negative bacteria appear red. The differences between these Two Types of bacteria are described in Section 2.5.1 (Cell wall).

Details of the Staining Procedure are provided in Experiment 12.2 in Section 12.9.

Last update: 06/08/2026

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