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 ?
Also the substantial agreement between Gram stain and culture highlights the importance of Gram stain in aetiological diagnosis in resource poor settings.
Comparison of bacterial antigen test and gram stain for detecting classic meningitis bacteria in cerebrospinal fluid.
Matching of the results of clue cells in the Gram stain and isolation of G.
Patient showed no signs of improvement even after 2 weeks of ATT, so a planned fiberoptic bronchoscopy of the patient was carried out and BAL sample was taken and sent for Gram stain and culture.
Date and time of 4 processing events were recorded: (1) initial detection time (instrument signal or alarm), (2) Gram stain processing completed, (3) Gram stain microscopic examination completed and results ready to be reported, and (4) results successfully reported to appropriate clinical staff.
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.
Reproducibility of a scoring system for gram stain diagnosis of bacterial vaginosis.
But the most significant part of the Gram stain is the presence of a homogenous distribution of bacteria, not a collection for three to five different types of organisms.
gonorrhoeae, along with Trichomonas vaginalis wet preps and genital Gram stains performed on patients seen in an emergency department between January 2004 and December 2004.
In addition to coverage of specific infections, there is also material on basic concepts such as the use of a gram stain, interpretation of bacterial cultures, the meaning of a minimal inhibital concentration, and specific drugs and dosages.
In a study of 116 patients presenting with an exacerbation of COPD, the combination of a negative sputum Gram stain, a nonclinical decrease in lung function, and fewer than two exacerbations in the previous 12 months was 100% predictive of a nonbacterial exacerbation.
A Gram stain of the vaginal secretions was obtained upon admission to labor and delivery.