Gram's stain

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Related to Gram stain: Gram negative, Gram positive

Gram's stain,

laboratory staining technique that distinguishes between two groups of bacteria by the identification of differences in the structure of their cell walls. The Gram stain, named after its developer, Danish bacteriologist Christian Gram, has become an important tool in bacterial taxonomy, distinguishing between so-called gram-positive bacteria, which remain colored after the staining procedure, and gram-negative bacteria, which do not retain dye. In the staining technique, cells on a microscope slide are heat-fixed (killed) and stained with a basic dye, crystal violet, which stains all bacterial cells blue; then they are treated with an iodine-potassium iodide solution that allows the iodine to enter the cells and form a water-insoluble complex with the crystal violet dye. The cells are treated with alcohol or acetone solvent in which the iodine-crystal violet complex is soluble. Following solvent treatment, only gram-positive cells remain stained, possibly because of their thick cell wall, which is not permeable to solvent. After the staining procedure, cells are treated with a counterstain, i.e., a red acidic dye such as safranin or acid fuchsin, in order to make gram-negative (decolorized) cells visible. Counterstained gram-negative cells appear red, and gram-positive cells remain blue. Although the cell walls of gram-negative and gram-positive bacteria are similar in chemical composition, the cell wall of gram-negative bacteria is a thin layer sandwiched between an outer lipid-containing cell envelope and the inner cell membrane, whereas the gram-positive cell wall is much thicker, lacks the cell envelope, and contains additional substances, such as teichoic acids, polymers composed of glycerol or ribitol. The difference in reactivity between gram-positive and gram-negative bacteria is linked with differences in physiological properties of the two groups. Gram-positive bacteria are generally more sensitive to growth inhibition by dyes, halogens, many antibioticsantibiotic,
any of a variety of substances, usually obtained from microorganisms, that inhibit the growth of or destroy certain other microorganisms. Types of Antibiotics
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, and to attack by phagocytosis (see endocytosisendocytosis
, in biology, process by which substances are taken into the cell. When the cell membrane comes into contact with a suitable food, a portion of the cell cytoplasm surges forward to meet and surround the material and a depression forms within the cell wall.
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), and are more resistant to digestion by the enzymes pepsinpepsin,
enzyme produced in the mucosal lining of the stomach that acts to degrade protein. Pepsin is one of three principal protein-degrading, or proteolytic, enzymes in the digestive system, the other two being chymotrypsin and trypsin.
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 and trypsintrypsin,
enzyme that acts to degrade protein; it is often referred to as a proteolytic enzyme, or proteinase. Trypsin is one of the three principal digestive proteinases, the other two being pepsin and chymotrypsin.
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 and enzymes in animal sera.

Gram's stain

[′gramz ‚stān]
(microbiology)
A differential bacteriological stain; a fixed smear is stained with a slightly alkaline solution of basic dye, treated with a solution of iodine in potassium iodide, and then with a neutral decolorizing agent, and usually counterstained; bacteria stain either blue (gram-positive) or red (gram-negative).
References in periodicals archive ?
POCARED will demonstrate the platform that provides both gram stain and second to-none cell recovery, viability, and robust fractionation capabilities.
Before implementation of the BC-GP (pre-BC-GP), critical calls were made at the time of the Gram stain.
Past gram stain automation options do not meet these three criteria.
Ventana is dedicated to providing laboratories, pathologists and their patients with novel assays, and we are empowering our customers to achieve greater efficiencies by automating common, yet labor-intensive tests like the Gram stain," says Mara G.
Laboratory standard operating procedures for the analysis of CSF require a white cell differential and Gram stain to be performed on samples with a white cell count of [greater than or equal to]5x[10.
Reliability of diagnosing bacterial vaginosis is improved by a standardized method of gram stain interpretation.
Characteristics that are important to note on the sputum Gram stain are very few squamous epithelial cells (less than 25 per low per field, or one to two per high oil field).
WASHINGTON -- Genital Gram stains alone lack the diagnostic ability to detect Chlamydia trachomatis and Neisseria gonorrhoeae infections, based on data from 1,511 emergency department visits, reported Dr.
3] with predominance of neutrophils, a positive CSF Gram stain or culture result, or both, and was further defined as nosocomial according to the 1988 guidelines of the Centers for Disease Control (10) in cases that occurred greater than 48 hours after hospital admission.
All bacterial isolates were characterized based on their gram stain, morphology, and utilization of various carbon sources using the BIOLOG system.
After isolating single bacterial colonies on several kinds of compatible agar, we were able to gram stain all samples.
A variety of diagnostic techniques were used; the analyses were based on the 1,938 women who had complete data for assessment of bacterial vaginosis according to Nugent Gram stain criteria.