What are the three basic Theories on the principle of gram staining reactions?

Answer 1

The gram stain is a basic differential stain used to determine if a bacterial cell is gram positive or negative. Gram positive cells have a thick peptidoglycan layer that will trap the crystal violet iodine crystalls and apear purple. Gram negative cells only have a thin peptidoglycan layer that allows the crystals to diffuse out of the cell and will only be seen with the application of a counterstain, such as safranin which turns the cells pink.

Answer 2

The gram stain is a basic differential stain used to determine if a bacterial cell is gram positive or negative. Gram positive cells have a thick peptidoglycan layer that will trap the crystal violet iodine crystalls and apear purple. Gram negative cells only have a thin peptidoglycan layer that allows the crystals to diffuse out of the cell and will only be seen with the application of a counterstain, such as safranin which turns the cells pink.

Answer 3

Gram staining (or Gram's method) is an empirical method of differentiating bacterial species into two large groups (Gram-positive and Gram-negative) based on the chemical and physical properties of their cell walls.[1]

The method is named after its inventor, the Danish scientist Hans Christian Gram (1853 - 1938), who developed the technique in 1884 to discriminate between pneumococci and Klebsiella pneumoniae bacteria.[2]

Gram-positive bacteria have a thick mesh-like cell wall made of peptidoglycan (50-90% of cell wall), which stain purple and Gram-negative bacteria have a thinner layer (10% of cell wall), which stain pink. Gram-negative bacteria also have an additional outer membrane which contains lipids, and is separated from the cell wall by the periplasmic space. There are four basic steps of the Gram stain, which include applying a primary stain (crystal violet) to a heat-fixed smear of a bacterial culture, followed by the addition of a mordant (Gram's iodine), rapid decolorization with alcohol or acetone, and counterstaining with safranin or basic fuchsin.

Crystal violet (CV) dissociates in aqueous solutions into CV+ and chloride (Cl - ) ions. These ions penetrate through the cell wall and cell membrane of both Gram-positive and Gram-negative cells. The CV+ ion interacts with negatively charged components of bacterial cells and stains the cells purple. Iodine (I - or I3 - ) interacts with CV+ and forms large complexes of crystal violet and iodine (CV - I) within the inner and outer layers of the cell. When a decolorizer such as alcohol or acetone is added, it interacts with the lipids of the cell membrane. A Gram-negative cell will lose its outer membrane and the peptidoglycan layer is left exposed. The CV - I complexes are washed from the Gram-negative cell along with the outer membrane. In contrast, a Gram-positive cell becomes dehydrated from an ethanol treatment. The large CV - I complexes become trapped within the Gram-positive cell due to the multilayered nature of its peptidoglycan. The decolorization step is critical and must be timed correctly; the crystal violet stain will be removed from both Gram-positive and negative cells if the decolorizing agent is left on too long (a matter of seconds).

After decolorization, the Gram-positive cell remains purple and the Gram-negative cell loses its purple color. Counterstain, which is usually positively-charged safranin or basic fuchsin, is applied last to give decolorized Gram-negative bacteria a pink or red color.[7][8]

Some bacteria, after staining with the Gram stain, yield a Gram-variable pattern: a mix of pink and purple cells are seen. The genera Actinomyces, Arthobacter, Corynebacterium, Mycobacterium, and Propionibacterium have cell walls particularly sensitive to breakage during cell division, resulting in Gram-negative staining of these Gram-positive cells. In cultures of Bacillus, Butyrivibrio, and Clostridium a decrease in peptidoglycan thickness during growth coincides with an increase in the number of cells that stain Gram-negative[9] In addition, in all bacteria stained using the Gram stain, the age of the culture may influence the results of the stain.

Answer 4

Gram staining is the way for people to get knowledge about their specimen , if it is gram negative or gram positive. Gram positive have thick walls and stains purple, gram negative has thin walls and will turn pink after gram staining and bacteria with spores and endospores will show up clear or see through because it cant stain with gram staining dye.

Answer 5

The gram stain is a basic differential stain used to determine if a bacterial cell is gram positive or negative. Gram positive cells have a thick peptidoglycan layer that will trap the crystal violet iodine crystalls and apear purple. Gram negative cells only have a thin peptidoglycan layer that allows the crystals to diffuse out of the cell and will only be seen with the application of a counterstain, such as safranin which turns the cells pink.

Answer 6

The three basic theories on the principle of Gram staining reactions are the physical-chemical theory, the chemical theory, and the biochemical theory. The physical-chemical theory suggests that the cell wall structure of bacteria determines their staining characteristics. The chemical theory proposes that the cell wall components interact with the crystal violet and iodine in the stain to form a complex compound. The biochemical theory suggests that the ability of bacteria to retain the crystal violet-iodine complex is due to the differences in their cell wall composition.