Differences Between Gram Positive and Gram Negative Bacteria

Bacteria are a huge group of single-celled microscopic organisms categorized as prokaryotic cells (lack true nucleus). Their inner structure is simple composing mainly of capsule, cellular wall, cytoplasm, ribosomes, DNA, pili, and flagellum. Bacteria can either be a gram-positive or gram-negative, and to find it out, a gram-staining technique has to be used.

Gram Staining technique is the most important and widely used microbiological differential staining technique. It categorizes bacteria according to their Gram character (Gram positive or Gram negative).

Along with their staining characteristics, Gram Positive and Gram Negative bacteria differ from each other in various aspects which are listed below :

S.N.	Characteristics	Gram Positive	Gram Negative
1.	Gram Reaction	Retain crystal violet dye and stain blue or purple.	Accept safranin and stain pink or red
2.	Cell Wall Structure	Structure of Gram Positive cell wall :	Structure of Gram Negative cell wall :
3.	Cell Wall Thickness	Thick (20-80 nm)	Thin (8-10 nm)
4.	Chemical Composition of Cell Wall	Peptidoglycan, Teichoic acid Lipotechoic acid	Lipopolysaccharide, Lipoproteins and Peptidoglycans
5.	Peptidoglycan Layer	Thick (Multilayered)	Thin (Single layered)
6.	Teichoic Acid in Cell Wall	Present	Absent
7.	Lipopolysaccharide Layer (Outer Layer)	Absent	Present
8.	Lipid Content	Absent or lower content of lipids than Gram Negative bacteria	Contains higher content of lipids than Gram positive bacteria (due to presence of outer membrane)
9.	Porin Proteins	Absent	Present
10.	Flagellar Structure	2 rings in basal body	4 rings in basal body
11.	Periplasmic Space	Absent	Present
12.	Mesosome	More prominent	Less prominent
13.	Ratio of RNA:DNA	8:1	Almost 1
14.	Toxins Produced	Primarily Exotoxins	Endotoxins and Exotoxins (Primarily Endotoxins)
15.	Resistance to Physical Disruption	High	Low
16.	Cell Wall Disruption by Lysozyme	High. After digestion of peptidoglycan layer, Gram +ve bacteria become Protoplast.	Low. After digestion of peptidoglycan layer, Gram -ve bacteria become Spheroplast.
17.	Susceptibility to Penicilin and Sulphonamide	High	Low
18.	Susceptibility to Streptomycin, Chloramphenicol and Tetracycline	Low	High
19.	Inhibition by Basic Dyes	High	Low
20.	Susceptibility to ionic detergents	High	Low
21.	Resistance to Sodium Azide	High	Low
22.	Resistance to Drying	High	Low
23.	Isoelectric Range pH	2.5-4.0	4.5-5.5
24.	Nutritional Requirements	Relatively Complex	Relatively Simple
25.	Rendering	They can rendered Gram -ve by increasing acidity	They can rendered Gram +ve by increasing alkalinity
26.	Morphology	Usually cocci or spore forming rods (exception : Lactobacillus and Corynebacterium)	Usually non-spore forming rods (Exception : Neisseria)
27.	Examples	Staphylococcus Streptococcus Bacillus Clostridium Nocardia Propionibacterium Enterococcus Corynebacterium Listeria Lactobacillus Gardnerella	Escherichia Salmonella Klebsiella Proteus Helicobacter Hemophilus Vibrio Shigella Neisseria Enterobacter Pseudomonas

Frequently Asked Questions

What are the examples of gram-positive bacteria?

Some of the common gram-positive bacteria you will encounter in the healthcare setting as they are the leading causes of clinical infections are:

• Staphylococcus

• Streptococcus

• Bacillus

• Clostridium

• Nocardia

• Propionibacterium

• Enterococcus

• Corynebacterium

• Listeria

• Lactobacillus

• Gardnerella

Which is more harmful- gram-positive bacteria or gram-negative bacteria?

Of the two, gram-negative bacteria are more harmful as their outer membranes are protected by a slim layer hiding antigens present in the cell. If the infection is caused by gram-negative bacteria, it would require a strong dose of antibiotics and strict compliance to the course of treatment to thoroughly get rid of the harmful bacteria.

Is it easier to kill gram-positive bacteria?

Yes. Gram-positive bacteria’s cell wall can easily absorb antibacterial cleaning products and antibiotics because of their outer peptidoglycan layer.

What infections are caused by gram-positive bacteria?

Some of the infections caused by gram-positive bacteria include the following:

• Urinary tract infection
• Tuberculosis
• Diphtheria

What infections are caused by gram-negative bacteria?

Some of the infections caused by gram-negative bacteria are:

• Bloodstream infections
• Pneumonia
• Meningitis

Is E coli gram positive?

No. It is a rod-shaped gram-negative bacterium.

What kills gram negative bacteria?

Gram-negative bacteria are more difficult to destroy than gram-positive. The most effective approach is to use a combination therapy, especially antibiotics with dual-mechanism action.

Are gram negative bacteria curable?

Yes. It needs a strong dose of antibiotic and combination treatment to thoroughly destroy the pathogen.

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• Difference between Endotoxin and Exotoxin