Bacteria are microscopic organisms, typically a few micrometers in length. They have a wide range of shapes, ranging from spheres to rods and spirals. They are present in most habitats on Earth, and grow in soil, water, organic matter, and also in plants and animals. They are broadly classified as gram-negative and gram-positive depending on their cell wall structure, and a few other characteristics. The gram staining method is widely used to differentiate between both these bacterial species. It is an important step in the process that is routinely followed to identify a bacterial species as either of the two categories.
When carrying out this study, the property of the species to take on a particular color or stain is used as the basis of differentiation. This method is named after its inventor called Hans Christian Gram. This laboratory technique is mainly used to test bodily fluids under conditions where an infection is suspected, and the time factor is crucial. It works faster for the purpose of differentiating in many conditions.
Apart from the effect of gram staining, both types of bacteria differ in various other characteristics.
Wall Structure: The main difference between them is the arrangement of the outer structure of the cell.
Effect of Dye: A crystal violet dye solution is added to the bacteria to find their type. This process is known as gram staining.
Effect of Antibiotics: Identification of bacterial type is imperative for the treatment of medical conditions, since different bacteria have differing responses to antibiotics like penicillin.
Flagellum: A flagellum is a hair-like structure, which is used by the bacteria for locomotion.
Teichoic Acids: They are strong acidic polymers found in the cell wall. Their main function is to provide rigidity to this wall.
Liproproteins: Bacterial lipoproteins are a set of membrane proteins, which play an important role in various bacterial diseases caused by gram-negative and gram-positive bacteria.
Periplasmic Space: It is present between the layers of peptidoglycan and the secondary cell membrane.
The following table gives a detailed distinguishing points between the gram-negative and gram-positive bacteria.
|Characteristic||Gram-negative Bacteria||Gram-positive Bacteria|
|Wall Structure||They have a thin lipopolysaccharide exterior cell wall.||The peptidoglycan layer or the mesh-like structure that is seen outside the plasma membrane in these bacteria is quite thick. It is made up of close to twenty times the amount of peptidoglycan, which is present in gram negative bacteria.|
|Effect of Dye||They do not retain the crystal violet dye, and react only with a counter-stain. They generally stain pink.||They retain the crystal violet dye, and change into purple during staining identification.|
|Effect of Antibiotics||Bacterial cells are resistant to penicillin, and contain an endotoxin called LPS, which forms a coating on the outer cell wall surface, and protects the inner cell structures from invasions.||These bacteria can be neutralized by administration of penicillin. This antibiotic is still used for treating many gram-positive bacterial infections.|
|Flagellum||If present, the flagellum has four supporting rings, namely 'L' ring, 'P' ring, 'M' ring, and 'S' ring.||The flagellum has two supporting rings, one in the peptidoglycan layer, and the other in the plasma membrane. Since these bacteria already have a thick cell wall that is enough for support, the two additional rings are not required.|
|Teichoic Acids||These compounds are absent.||These acids are present.|
|Liproproteins||They are attached to the polysaccharide backbone.||They are absent.|
|Periplasmic Space||It is present.||It is absent.|
Gram staining method still continues to be the first step for many routine procedures to identify bacterial species, but there are some organisms that are gram variable, or gram indeterminate. Therefore, they cannot be subjected to this test. In addition, this test has now been replaced by more sophisticated methods that use genetic sequences and molecular structures, which are widely recognized as more reliable methods of species identification.