1. Classification by Structure
Eubacteria cell walls are made of Peptidoglycan.
Thickness of cell wall and other membranes protects bacteria against some kinds of antibiotics by preventing their entry into the cell.

2. Gram Stain
Most species of bacteria can be grouped into 2 categories based on their response to a laboratory technique called Gram Staining
Taxonomists divide bacteria
into various subgroups
including Gram-Positive
& Gram-Negative Bacteria

3. Gram Stain
Technique involves staining bacteria with purple dye (Crystal violet) & iodine
Then rinsed with alcohol
Then restained with a red dye (Safranin)
Gram-Positive Bacteria will retain the PURPLE DYE and appear Purple.
Gram-Negative Bacteria will appear RED (pink) from the RED DYE
Depending on cell walls, bacteria absorbs either purple/red dye

4. Gram Stain
Gram-Positive bacteria have thicker layer of peptidoglycan in cell wall
Gram-Positive and Negative differ insusceptibilities to antibacterial drugs, produce different toxic materials, & react differently to disinfectants.
Gram + (top), Gram – (bottom)
Note: Gram-negative bacteria have cell wall including an outer membrane composed of a layer of lipids and sugars: “glycocalyx”