Comparative Characteristics of Gram-Positive

and Gram-Negative Bacteria

Characteristic

Gram-positive

Gram-negative

Gram reaction

Retain crystal violet dye and stain dark violet or purple

Can be decolorized to accept counterstain (safranin); stain red

Peptidoglycan layer

Thick (multilayered)

Thin (single-layered)

Teichoic acids

Present in many

Absent

Periplasmic space

Absent

Present

Outer membrane

Absent

Present

Lipopolysaccharide (LPS) content

Virtually none

High

Lipid and lipoprotein content

Low (acid-fast bacteria have lipids linked to peptidoglycan)

High (due to presence of outer membrane)

Flagellar structure

2 rings in basal body

4 rings in basal body

Toxins produced

Primarily exotoxins

Primarily endotoxins

Resistance to physical disruption

High

Low

Inhibition by basic dyes

High

Low

detergents

High

Low

Resistance to sodium azide

High

Low

Resistance to drying

High

Low