What it teaches

The Gram stain as a differential procedure: what each of the four reagents does, why the order is fixed, and why decolorization is the step that decides the result. Scoped to entry-level bench training.

Sources

Bench durations follow the CDC How to Perform a Gram Stain job aid and the ASM Gram Stain Protocols: 15 s crystal violet, 15 s iodine, 30 s safranin.

The decolorizer carries no stated duration on purpose. CDC cues it on runoff clarity, which varies with decolorizer formulation and smear thickness, so the module models the runoff rather than printing a number that does not exist.

Decolorization here is tuned for 95% ethanol. A commercial acetone-alcohol decolorizer runs considerably faster.

What it deliberately omits

• Reagent formulation variants (Hucker's and Kopeloff's)
• Decolorizer strength differences (95% ethanol, acetone-alcohol, acetone)
• Fixation method alternatives (heat versus methanol)
• Gram-variable organisms and loss of gram-positivity in ageing cultures
• Organisms the stain cannot resolve, including Mycobacteria and cell-wall-free Mycoplasma
• Quality-control organisms and specimen-type variation

These are omitted so the core procedure stays legible, not because they are unimportant. Each one belongs in training that follows this.