Differences between Gram Positive and Gram negative bacteria

Bacteria are classified as Gram-positive and Gram-negative based on their response to the Gram staining technique, which relies on differences in their cell wall structure. This classification is essential in microbiology for identifying bacteria and determining their susceptibility to antibiotics.

Gram Positive Bacteria

• Stain dark purple because the thick peptidoglycan layer in their cell wall retains the primary stain, Crystal violet, even after being washed with alcohol.
• Have a simpler cell wall structure without an outer membrane.
• Example: Staphylococcus aureus, a common bacterium responsible for skin infections and other diseases.

Gram Negative Bacteria

• Stain red or pink because they do not retain the Crystal violet dye but instead take up the counterstain, Safranin. This happens due to their thin peptidoglycan layer and the presence of an outer membrane.
• Possess a more complex cell wall structure, making them more resistant to certain antibiotics.
• Example: Escherichia coli, a bacterium commonly found in the intestines, some strains of which can cause food poisoning.

Detailed Differences Between Gram Positive and Gram Negative Bacteria

Feature	Gram Positive Bacteria	Gram Negative Bacteria
Staining	Retain Crystal violet; stain purple.	Decolorized, retain Safranin; stain pink/red.
Peptidoglycan Layer	Thick, multilayered (20-80 nm), forming up to 90% of the cell wall.	Thin, single-layered (2-10 nm), forming about 10% of the cell wall.
Outer Membrane	Absent.	Present; contains lipopolysaccharides (LPS).
Periplasmic Space	Absent.	Present between the outer membrane and the cytoplasmic membrane.
Teichoic Acids	Present; provide rigidity and play a role in ion transport.	Absent.
Lipid Content	Low (1-4%).	High (11-22%), contributing to their structural complexity.
Resistance to Disruption	High resistance to physical disruption and drying due to the thick cell wall.	Low resistance to physical disruption and drying.
Cell Wall Thickness	100-120 Å; single-layered.	70-120 Å; two-layered with an additional outer membrane.
Antibiotic Susceptibility	More susceptible to antibiotics like penicillin due to lack of outer membrane.	More resistant due to the protective outer membrane.
Toxins Produced	Primarily exotoxins, which are secreted proteins.	Primarily endotoxins (lipopolysaccharides in the outer membrane).
Flagella Structure	If present, flagella have two basal body rings.	If present, flagella have four basal body rings.

 

Significance of These Differences

1. Pathogenicity: Gram-negative bacteria are often more pathogenic due to their lipopolysaccharide layer, which can trigger strong immune responses.

2. Antibiotic Resistance: The outer membrane of Gram-negative bacteria acts as a barrier to many antibiotics and detergents, making infections harder to treat.

3. Staining for Diagnosis: The Gram stain is a rapid and inexpensive diagnostic tool used to guide initial treatment decisions for bacterial infections.