![]() ![]() Staining mechanism Purple-stained gram-positive (left) and pink-stained gram-negative (right) Gram stains yield results much more quickly than culturing, and are 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. Gram stains are performed on body fluid or biopsy when infection is suspected. Furthermore, for cases having undergone culture, Gram stain is shown as a major determinant for further workup. In this setting, Gram stain is used even before agar plate cultures for blood and cerebrospinal fluid specimens. Medical Example of a workup algorithm of possible bacterial infection in cases with no specifically requested targets (non-bacteria, mycobacteria etc.), with most common situations and agents seen in a New England community hospital setting. 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. 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. Gram staining is not used to classify archaea, since these microorganisms yield widely varying responses that do not follow their phylogenetic groups. Gram staining is a bacteriological laboratory technique used to differentiate bacterial species into two large groups ( gram-positive and gram-negative) based on the physical properties of their cell walls. The small oval chlamydospores are 2–4 µm in diameter. Uses Gram stain of Candida albicans from a vaginal swab. ![]() He published his method in 1884, and included in his short report the observation that the typhus bacillus did not retain the stain. 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. The method is named after its inventor, the Danish scientist Hans Christian Gram (1853–1938), who developed the technique while working with Carl Friedländer in the morgue of the city hospital in Berlin in 1884. This gives rise to gram-variable and gram-indeterminate groups. While Gram staining is a valuable diagnostic tool in both clinical and research settings, not all bacteria can be definitively classified by this technique. ![]() Gram staining is almost always the first step in the identification of a bacterial group. Lugol's iodine solution is always added after addition of crystal violet to strengthen the bonds of the stain with the cell membrane. They are stained pink or red by the counterstain, commonly safranin or fuchsine. Gram-negative cells have a thinner peptidoglycan layer that allows the crystal violet to wash out on addition of ethanol. Gram-positive cells have a thick layer of peptidoglycan in the cell wall that retains the primary stain, crystal violet. Gram staining differentiates bacteria by the chemical and physical properties of their cell walls. The name comes from the Danish bacteriologist Hans Christian Gram, who developed the technique in 1884. ![]() In microbiology and bacteriology, Gram stain ( Gram staining or Gram's method), is a method of staining used to classify bacterial species into two large groups: gram-positive bacteria and gram-negative bacteria. coli ATCC 11775, gram-negative bacilli, in red), the most common Gram stain reference bacteria aureus ATCC 25923, gram-positive cocci, in purple) and Escherichia coli ( E. Investigative procedure in microbiology A Gram stain of mixed Staphylococcus aureus ( S. ![]()
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