Basis of differentiation 

Gram positive cell wall 

Gram negative cell wall

Definition

Refers to the cell wall of Gram positive bacteria

Refers to the cell wall of Gram negative bacteria

Number of peptidoglycan layers

Multilayered peptidoglycan layer

Single peptidoglycan layer

Thickness of peptidoglycan layer

Thick peptidoglycan layer about 15 to 80 nm

Thin peptidoglycan layer about 8-12 nm

Outer membrane

Absent

Present 

Teichoic acids 

Present 

Absent 

Porin proteins

Absent 

Present in the outer membrane

Periplasmic space

Negligible or absent 

Present 

Lipopolysaccharide concentration 

Low 

High 

Outcome of Gram staining

Stains purple in color

Stains pink in color

Retention of crystal violet 

Retains crystal violet

Does not retain crystal violet

Resistance against antibiotics 

Less resistant

Highly resistant 

Toxicity 

Less toxic 

More toxic