What is gram-negstive?

Answer 1

There are two categories of bacteria, gram-positive and gram-negative. They are categorized based on the structural differences of their cell wall.

While gram-(+) only have one layer of membrane, gram-(-) has an outer and inner membrane. The thick lipid bilayer making up the outer membrane is harder to penetrate with antibiotics.

Staining

• Gram-(+) retains crystal violet dye after being washed with solution and will appear purple. This happens because it's membrane is 50-90% peptidolglycan, a sugar and peptide.
• Gram-(-) does not retain the crystal violet dye after being washed with solution and will appear pink because of the counter-stain in the solution, usually Safranin. This happens because the outer membrane is only ~10% peptidolglycan.

Pathogenic Properties

• Gram-(-) have lipopolysaccharides (LPS) made up of toxic fatty acids (lipid A) and a polysaccharide (which includes antigen O) in their outer membrane. LPS at high levels in the body causes septic shock.

Antibiotic resistance:

Both gram-(+) and gram-(-) can show antibiotic resistance.

Gram-(-) is more likely to show antibiotic resistance because:

1. Their outer membrane (see above)
2. They generally have greater facility in exchanging DNA among other cells of the same species.

Examples:

• Some gram-(+) bacteria: streptococcal, staphylococcal
• gram-(+) types can cause: step throat, toxic shock, blood poisoning
• Some gram-(-) bacteria: shigella, salmonella, E. coli
• gram-(-) types can cause: pneumonia, gonorrhea,