Photo courtesy of the US CDC Gram staining is a common technique used to differentiate two large groups of bacteria based on their different cell wall constituents. The Gram stain procedure distinguishes between Gram positive and Gram negative groups by coloring these cells red or violet. Gram positive bacteria stain violet due to the presence of a thick layer of peptidoglycan in their cell walls, which retains the crystal violet these cells are stained with. Alternatively, Gram negative bacteria stain red, which is attributed to a thinner peptidoglycan wall, which does not retain the crystal violet during the decoloring process.
Gram devised his technique not for the purpose of distinguishing one type of bacterium from another but to make bacteria more visible in stained sections of lung tissue.
It is used mainly to make a preliminary morphologic identification or to establish that there are significant numbers of bacteria in a clinical specimen.
It cannot identify bacteria to the species level, and for most medical conditions, it should not be used as the sole method of bacterial identification. In clinical microbiology laboratories, it is used in combination with other traditional and molecular techniques to identify bacteria. Some organisms are gram-variable meaning they may stain either negative or positive ; some are not stained with either dye used in the Gram technique and are not seen.
In a modern environmental or molecular microbiology lab, most identification is done using genetic sequences and other molecular techniques, which are far more specific and informative than differential staining. Gram staining has been suggested to be as effective a diagnostic tool as PCR in one primary research report regarding gonococcal urethritis.
Gram-negative bacterial infection and Gram-positive bacterial infection Gram stains are performed on body fluid or biopsy when infection is suspected. Gram stains yield results much more quickly than culturingand is especially important when infection would make an important difference in the patient's treatment and prognosis; examples are cerebrospinal fluid for meningitis and synovial fluid for septic arthritis.
There are four basic steps of the Gram stain: Applying a primary stain crystal violet to a heat-fixed smear of a bacterial culture. Heat fixation kills some bacteria but is mostly used to affix the bacteria to the slide so that they don't rinse out during the staining procedure The addition of iodidewhich binds to crystal violet and traps it in the cell Rapid decolorization with ethanol or acetone Counterstaining with safranin.
These ions penetrate through the cell wall and cell membrane of both gram-positive and gram-negative cells. Iodine is often referred to as a mordantbut is a trapping agent that prevents the removal of the CV—I complex and, therefore, color the cell.
The CV—I complexes are washed from the gram-negative cell along with the outer membrane. The large CV—I complexes become trapped within the gram-positive cell due to the multilayered nature of its peptidoglycan.Jan 22, · Gram staining is a quick procedure used to look for the presence of bacteria in tissue samples and to characterise bacteria as Gram-positive or Gram-negative, based on the chemical and physical properties of their cell walls%(10).
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Amount and location of peptidoglycan in the prokaryotic cell wall determines if a bacterium is Gram-positive or Gram-negative.
Photos and video. A Gram stain is a lab test used to detect bacteria or fungi in a sample taken from the site of a suspected infection. It gives relatively quick, preliminary results as to whether microbes are present and, if so, the general type(s) causing an infection.
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Gram Staining Introduction. The gram stain permits the separation of all bacterial species into two large groups, those which retain the primary dye (gram-positive), and those which lose the primary dye and take the color of the secondary dye (gram-negative).