Gram-Positive vs. Gram-Negative

What is the main component of the bacterial cell wall?

Peptidoglycan.

What is the function of the bacterial cell wall?

It determines cell shape and prevents lysis from changing osmotic pressures.

What is the main structural difference between Gram-positive and Gram-negative cell walls?

Gram-positive cells have a thick peptidoglycan wall, while Gram-negative cells have a thin peptidoglycan layer and an outer membrane.

What is found in the Gram-positive cell wall besides peptidoglycan?

Teichoic acid and lipoteichoic acid.

How thick is the Gram-positive peptidoglycan layer?

About 20–80 nm.

What is found in the outer membrane of Gram-negative bacteria?

Lipopolysaccharide (LPS).

What part of LPS is endotoxin?

The lipid portion.

What are porins?

Proteins in the Gram-negative outer membrane that regulate molecules entering and leaving the cell.

Which bacterial group has an outer membrane?

Gram-negative bacteria.

Which bacterial group has the thicker peptidoglycan layer?

Gram-positive bacteria.

Which bacterial group has an extensive periplasmic space?

Gram-negative bacteria.

Which bacterial group is more penetrable to molecules?

Gram-positive bacteria.

What is the Gram stain?

A differential stain that distinguishes Gram-positive from Gram-negative bacteria.

What color are Gram-positive bacteria after Gram staining?

Purple.

What color are Gram-negative bacteria after Gram staining?

Pink.

Why do Gram-positive bacteria stain purple?

They retain crystal violet.

Why do Gram-negative bacteria stain pink?

They lose crystal violet and take up the safranin counterstain.

What is an acid-fast stain used to diagnose?

Infections caused by organisms such as Mycobacterium and Nocardia.

What is unusual about Mycoplasma?

It lacks a cell wall.

What stabilizes the cell membrane of Mycoplasma?

Sterols.