Gram positive and gram negative
organisms are two different types of bacteria that can be differentiated by a laboratory staining technique called the Gram stain. The key difference between these two types of bacteria is in their cell wall structure.
Gram positive bacteria have a thick peptidoglycan layer in their cell wall that retains the crystal violet stain used in the Gram staining process, making them appear dark purple under the microscope. They also have teichoic acids in their cell wall that help maintain its structure. Some examples of Gram positive bacteria include Staphylococcus aureus, Streptococcus pneumoniae, and Bacillus subtilis.
Gram negative bacteria, on the other hand, have a thinner peptidoglycan layer and an outer membrane that contains lipopolysaccharides and porins. These components make the cell wall more complex and resistant to certain antibiotics. Gram negative bacteria do not retain the crystal violet stain and instead appear pink or red under the microscope after being counterstained with safranin. Some examples of Gram negative bacteria include Escherichia coli, Salmonella typhi, and Pseudomonas aeruginosa.
Knowing whether a bacterium is gram positive or gram negative is important in determining appropriate treatment options, as different antibiotics target specific components of the cell wall.
Gram-positive and gram-negative are two types of bacteria that are distinguished by the way they react to a staining technique called the Gram stain. This staining method was developed by Hans Christian Gram in 1884 and is widely used in microbiology to identify and classify bacteria.
1. Gram-positive bacteria:
- Structure: Gram-positive bacteria have a thick cell wall composed mainly of peptidoglycan, a complex polymer made of sugars and amino acids. They also have a cytoplasmic membrane.
- Staining: When stained with the Gram stain, the cell wall retains the crystal violet dye, imparting a purple color to the bacteria.
- Retention of stain: Gram-positive bacteria retain the purple color even after the application of a decolorizing agent, such as ethanol or acetone.
- Examples: Common gram-positive bacteria include Staphylococcus aureus, Streptococcus pyogenes, and Clostridium difficile.
2. Gram-negative bacteria:
- Structure: Gram-negative bacteria have a thinner cell wall composed of a thin layer of peptidoglycan surrounded by an outer membrane. The outer membrane contains lipopolysaccharides (LPS) and porins.
- Staining: When stained with the Gram stain, the cell wall of gram-negative bacteria does not retain the crystal violet dye initially. Instead, it takes up a counterstain called safranin, which imparts a pink or red color to the bacteria.
- Loss of stain: Gram-negative bacteria lose the purple color when subjected to the decolorizing agent due to the thinner peptidoglycan layer. The outer membrane and LPS provide a barrier that prevents the retention of the crystal violet dye.
- Examples: Common gram-negative bacteria include Escherichia coli, Pseudomonas aeruginosa, and Salmonella enterica.
It is important to note that the classification into gram-positive and gram-negative bacteria is based on the staining characteristics and is not indicative of their pathogenic potential or clinical significance. Both types of bacteria can cause a range of infections and have different characteristics and responses to antibiotics.