1. Bacterial Cell Walls

2. Cell
membrane

5. Gram Stain The most widely used staining procedure in bacteriology.
Differential stain: differentiates between gram- positive and gram-negative bacteria.
Bacteria that stain-
purple are gram-positive
pink are gram-negative

7. Gram Stain Technique:
1. The bacteria are first stained with crystal violet.
2. The bacteria are then treated with gram's iodine solution. This allows the stain to be retained better by forming an insoluble crystal violet-iodine complex.
3. A decolorizer, ethanol or acetone, is then added. This is the differential step.
4. The counterstain safranin is applied. Since the gram-positive bacteria are already purple, they are not affected. Gram-negative bacteria become stained by the safranin.

9. http://faculty. ccbcmd
du/courses/bio141/lab manua/lab6/images/gr am_stain_11.swf
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