The differences in how bacterial cells are built play a big role in how we classify and identify them. This is really important for medical microbiology.

1. Cell Wall Composition:

   • Gram-positive Bacteria: These have a thick layer that helps them hold onto a blue dye called crystal violet when looked at under a microscope.
   • Gram-negative Bacteria: These have a much thinner layer that is trapped between two membranes. They lose the blue dye but take up a red dye called safranin.

2. Shapes:

   • Bacteria come in different shapes. They can be cocci (round), bacilli (rod-shaped), or spirilla (spiral). About 70% of bacteria that can make people sick are round (cocci).

3. Extra Structures:

   • Some bacteria have special features like capsules (which can be thick), flagella (long tails that help them move), and pili (tiny hair-like structures). These features help bacteria stick to places and can make them more harmful. Around 75% of bacteria that cause disease have one or more of these special features.

4. Genetic Material:

   • Most bacteria have one ring of DNA. They can also have small circles of DNA called plasmids, which can give them some extra abilities, like resisting antibiotics. About 50% of harmful bacteria have plasmids.

These differences in structure help scientists group bacteria and understand how dangerous they can be. This knowledge is really important for figuring out how to diagnose and treat infections.