A staining technique for the preliminary identification of bacteria, in which a violet dye is applied, followed by a decolorizing agent and then a red dye. The cell walls of certain bacteria (denoted Gram-positive) retain the first dye and appear violet, while those that lose it (denoted Gram-negative) appear red. Also called Gram’s method.
- The use of standard biochemical testing rather than commercial systems has been recommended for identification of Gram-negative nonfermenting bacteria.
- Endotoxin, the highly inflammatory surface component of Gram-negative bacteria, has been previously implicated in the morbidity and mortality of a number of clinical settings, including patients undergoing cardiac surgery.
- Moreover, single findings can occasionally be very powerful and definitive, just as the results of certain formal diagnostic tests (such as a spinal fluid Gram stain showing bacteria).
Late 19th century: named after Hans C. J. Gram (1853–1938), the Danish physician who devised the method.
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Syllabification: Gram stain
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