Differences between Gram Positive and Gram Negative Bacteria: Introduction, and Related Footages
Table of Contents
‘Gram-Positive Bacilli (GPB)‘ is also called Gram-Positive Rods (GPR) bacteria which retain crystal violet dye and stain blue or purple on Gram’s staining. The most common medically important bacteria of GPR are Mycobacterium tuberculosis, Mycobacterium leprae, Listeria monocytogenes, Nocardia asteroides, Actinomyces israelii, Bacillus anthracis, Bacillus cereus, Bifidobacterium species, Corynebacterium diphtheriae, and Clostridium species.
‘Gram-Positive Cocci (GPC)‘ bacteria retain crystal violet dye and stain blue or purple on Gram’s staining. The most common medically important bacteria of GPC are Staphylococcus aureus, Streptococcus pneumoniae, Enterococcus species, Streptococcus pyogenes, Streptococcus agalactiae, and Staphylococcus saprophyticus.
‘Gram-Positive Negative (GNB)‘ is also called Gram-Negative Rods (GNR) bacteria which take safranin after decolorization and stain pink or red on Gram’s staining. Most GNR bacteria are medically important and among them, a few are Escherichia coli, Klebsiella pneumoniae, Salmonella enterica serotype Typhi, Shigella species, Proteus species, Citrobacter, Pseudomonas aeruginosa, and Acinetobacter species.
Medically relevant gram-negative cocci bacteria are Neisseria gonorrhoeae (causative agent of sexually transmitted disease), Neisseria meningitidis (causes meningitis), Moraxella catarrhalis (responsible for respiratory symptoms), and Veillonella parvula (anaerobic gram-negative coccus cause osteomyelitis).
The differences between Gram-Positive and Gram-Negative Bacteria are summarized as follows-
| S. No. | Property | Gram-Positive Bacteria | Gram-Negative Bacteria |
| 1 | Gram Reaction | Take crystal violet (primary stain) and stain violet or purple on staining | Retain safranin (counterstain) after decolorization and stain pink or red on staining |
| 2 | Cell wall thickness | 20-80 nm | 8-10 nm |
| 3 | Peptidoglycan Layer | Multilayered (Thick) | single-layered (Thin) |
| 4 | Rigidity and Elasticity | Rigid and less elastic | Less rigid and more elastic |
| 5 | Outer Membrane | Absent | Present |
| 6 | Variety of amino acid in cell wall | Few | Several |
| 7 | Aromatic and Sulfur-containing amino acid in cell wall | Absent | Present |
| 8 | Periplasmic Space | Absent | Present |
| 9 | Teichoic Acids | Mostly present | Absent |
| 10 | Porins | Absent | Present |
| 11 | Lipopolysaccharide (LPS) Content | Almost None | High |
| 12 | Lipid and Lipoprotein Content | Low (acid-fast bacteria have lipids linked to peptidoglycan) | High (due to presence of outer membrane) |
| 13 | The ratio of RNA and DNA | 8:1 | Nearly 1 |
| 14 | Mesosomes | Fully Prominent | Less Prominent |
| 15 | Flagellar Structure | 2 rings in basal body | 4 rings in basal body |
| 16 | Magnetosomes | Usually absent | Sometimes present |
| 17 | Morphology | Normally cocci or spore-forming rods (except- Lactobacillus and Corynebacterium) | Usually non-spore-forming rods (Except-Neisseria) |
| 18 | Endospore formation | Some produce endospores during unfavorable conditions like Bacillus, Clostridium, Sacchropolyspora, Micromonospora, and Streptomyces. | Normally not producing endospores |
| 19 | Toxin Produced | Exotoxin | Endotoxin or Exotoxin |
| 20 | Pathogens | Only a few are pathogens. | Most of them are pathogens. |
| 21 | Nutritional Requirements | Relatively Complex | Relatively Simple |
| 22 | Resistance to Physical Disruption | High | Low |
| 23 | Cell Wall Disruption by Lysozyme | High | Low ( since it requires pretreatment to destabilize outer membrane) |
| 24 | Susceptibility to Penicillin and Sulfonamide | Sulfonamide High | Low |
| 25 | Susceptibility to Streptomycin, Chloramphenicol, and Tetracycline | Low | High |
| 26 | Inhibition by Basic Dyes | High | Low |
| 27 | Susceptibility to Anionic Detergents | High | Low |
| 28 | Resistance to Sodium Azide | High | Low |
| 29 | Resistance to Drying | High | Low |
| 30 | Rendering | They can render Gram-negative by increasing acidity | They can render Gram-positive by increasing alkalinity |
| 31 | Common Examples | Staphylococcus aureus Streptococcus pnrumoniae Streptococcus pyogenes Streptococcus agalactiae Enterococcus species Bacillus Clostridium Listeria monocytogenes Corynebacterium diphtheriae | Escherichia coli Salmonella Typhi S. Paratyphi, Klebsiella pnumoniae, Proteus vulgaris, Helicobacter pylori Pseudomonas aeruginosa, Acinetobacter spp. |
| 32 | Common Infections | Pneumococcal infections Staphylococcal aureus infections Streptococcal infections Toxic shock syndrome Anthrax Diphtheria Enterococcal infections Erysipelothricosis Listeriosis | E. coli infections, Klebsiella infections, Haemophilus influenzae infections, Cholera, Plague, Typhoid fever, Shigellosis, Brucellosis, Pseudomonas infections, Campylobacter infections |
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