| gram-molecule | <unit> The amount of a substance with a mass in grams equal to its molecular weight; e.g., a gram-molecule of hydrogen weighs 2.016 g, that of water 18.015 g. (05 Mar 2000) |
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| gram-negative | <microbiology> A common class of bacteria normally found in the gastrointestinal tract that can be responsible for disease in man (sepsis). Bacteria are considered to be gram-negative because of their characteristic staining properties under the microscope, where they either do not stain or are decolourised by alcohol during Gram's method of staining. This is a primary characteristic of bacteria that have a cell wall composed of a thin layer of peptidoglycan covered by an outer membrane of lipoprotein and lipopolysaccharide containing endotoxin. The gram staining characteristics of bacteria have resulted in an important classification system for the identification of bacteria. See: gram-positive (06 Oct 1997) |
| gram-negative aerobic bacteria | <microbiology> A large group of aerobic bacteria which show up as pink (negative) when treated by the gram-staining method. (12 Dec 1998) |
| gram-negative aerobic rods and cocci | <microbiology> A group of gram-negative bacteria consisting of rod- and coccus-shaped cells. They are both aerobic (able to grow under an air atmosphere) and microaerophilic (grow better in low concentrations of oxygen) under nitrogen-fixing conditions but, when supplied with a source of fixed nitrogen, they grow as aerobes. (12 Dec 1998) |
| gram-negative anaerobic bacteria | <microbiology> A large group of anaerobic bacteria which show up as pink (negative) when treated by the gram-staining method. (12 Dec 1998) |
| gram-negative anaerobic cocci | <microbiology> A group of anaerobic coccoid bacteria that show up as pink (negative) when treated by the gram-staining method. (12 Dec 1998) |
| gram-negative anaerobic straight, curved, and helical rods | <microbiology> A group of anaerobic, rod-shaped bacteria that show up as pink (negative) when treated by the gram-staining method. (12 Dec 1998) |
| gram-negative bacteria | <microbiology> Bacteria which lose crystal violet stain but are stained pink when treated by gram's method. (12 Dec 1998) |
| gram-negative bacterial infections | <microbiology> Infections caused by bacteria that show up as pink (negative) when treated by the gram-staining method. (12 Dec 1998) |
| gram-negative chemolithotrophic bacteria | <microbiology> A large group of bacteria including those which oxidise ammonia or nitrite, metabolise sulfur and sulfur compounds, or deposit iron and/or manganese oxides. (12 Dec 1998) |
| gram-negative facultatively anaerobic rods | <microbiology> A large group of facultatively anaerobic, rod-shaped bacteria that show up as pink (negative) when treated by the gram-staining method. (12 Dec 1998) |
| gram-negative oxygenic photosynthetic bacteria | <microbiology> Widely distributed unicellular or multicellular bacteria. The cyanobacteria use chlorophyll a and phycobilins for oxygenic photosynthesis while genera in the prochlorales use both chlorophyll a and b but not phycobilins. (12 Dec 1998) |
| Gram's iodine | <microbiology> A solution containing iodine and potassium iodide, used in Gram's stain. (05 Mar 2000) |
| Gram's stain | <microbiology, technique> A method for differential staining of bacteria; smears are fixed by flaming, stained in a solution of crystal violet, treated with iodine solution, rinsed, decolorised, and then counterstained with safranin O. Gram-positive organisms stain purple black and Gram-negative organisms stain pink; useful in bacterial taxonomy and identification, and also in indicating fundamental differences in cell wall structure. (05 Mar 2000) |
| Gram stain | <microbiology, procedure> A method of staining bacteria using a violet stain. The gram staining characteristics (denoted as positive or negative) can assist in the identification of the offending bacteria. A heat fixed bacterial smear is stained with crystal violet (methyl violet), treated with 3% iodine/potassium iodide solution, washed with alcohol and counterstained. The method differentiates bacteria into two main classes, gram-positive and gram-negative. Certain bacteria, notably mycobacteria, that have walls with high lipid content show acid-fast staining the stain resists decolouration in strong acid. (27 Sep 1997) |