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What is Gram Staining?
Gram staining is a laboratory technique used to identify bacteria by staining their cell walls. The bacteria either appear purple or pink depending on their cell wall structure.
Gram-Positive Bacteria
Gram-positive bacteria have a thick layer of peptidoglycan in their cell walls, which gives them strength and stability. These bacteria also contain teichoic acids, which help in cell wall maintenance.
- Positivity: Gram-positive bacteria appear purple when stained with Gram stain.
- Examples:
- Staphylococcus aureus (can cause skin infections)
- Streptococcus pneumoniae (can cause pneumonia)
Properties of Gram-Positive Bacteria:
1. They have a thick peptidoglycan layer in their cell wall.
2. They do not have an outer membrane.
3. Teichoic acids are present, providing additional support.
4. These bacteria are generally more susceptible to antibiotics like penicillin.
Gram-Negative Bacteria
Gram-negative bacteria have a thin layer of peptidoglycan, and they are surrounded by an outer membrane containing lipopolysaccharides (LPS), which act as endotoxins.
- Negativity: Gram-negative bacteria appear pink/red after Gram staining.
- Examples:
- Escherichia coli (can cause food poisoning)
- Salmonella typhi (causes typhoid fever)
Properties of Gram-Negative Bacteria:
1. They have a thin peptidoglycan layer.
2. They have an outer membrane that provides additional protection.
3. Gram-negative bacteria are often more resistant to antibiotics due to their outer membrane.
Conclusion
- Gram-positive bacteria stain purple in Gram staining and have a thick peptidoglycan layer in their cell walls.
- Gram-negative bacteria stain pink/red and have a thin peptidoglycan layer along with an outer membrane, making them more resistant to antibiotics.
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