Feb 8, 2004 18:11
21 yrs ago
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English term
S Angel-Jones-Fitton
gram variable
English
Medical
Biology (-tech,-chem,micro-)
microbiology
what does it mean
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6 mins
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Give ambiguous or mixed results when stained
Gram stain is "a method for differential staining of bacteria; smears are fixed by flaming, stained in a solution of crystal violet, treated with iodine solution, rinsed, decolorized, 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" (Stedman's Medical Dictionary).
Some gram-positive bacteria give ambiguous or mixed results. They are called "gram-variable."
Some gram-positive bacteria give ambiguous or mixed results. They are called "gram-variable."
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+1
4 mins
gram variable
this glossary might help
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Note added at 2004-02-08 18:16:38 (GMT)
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Gram Variable: Some Gram-positive cells occur in an otherwise Gram-negative pure culture.
Gram-positive: To describe a prokaryotic cell whose cell wall stains purple (positive) in Gram stain. The cell wall of a gram-positive bacterium consists chiefly of peptidoglycan and lacks the outer membrane of gram-negative cells.
Gram-negative: To describe a prokaryotic cell whose cell wall stains pink (negative) in Gram stain. The cell wall of a gram-negative bacterium contains relatively little peptidoglycan but contains an outer membrane composed of lipopolysaccharide (LPS), lipoprotein, and other complex macromolecules.
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Note added at 2004-02-08 18:16:38 (GMT)
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Gram Variable: Some Gram-positive cells occur in an otherwise Gram-negative pure culture.
Gram-positive: To describe a prokaryotic cell whose cell wall stains purple (positive) in Gram stain. The cell wall of a gram-positive bacterium consists chiefly of peptidoglycan and lacks the outer membrane of gram-negative cells.
Gram-negative: To describe a prokaryotic cell whose cell wall stains pink (negative) in Gram stain. The cell wall of a gram-negative bacterium contains relatively little peptidoglycan but contains an outer membrane composed of lipopolysaccharide (LPS), lipoprotein, and other complex macromolecules.
8 mins
David Russi
United States
United States
Native in English
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English
United States
30+ years, stopped counting...
Native in: English 
, Spanish
Works in: English to Spanish, Spanish to English
Organisms that sometimes retain the blue colour [of tand sometimes do not are known as gram-variable
From the link below:
The best known and most widely used bacteriological staining method, it is almost always the first test performed for the identification of bacteria.
The primary stain of the Gram's method is crystal violet. Crystal violet is sometimes substituted with methylene blue, which is equally effective. Bacteria are first stained with the crystal violet and then treated with Lugol's solution, consisting of 1 part iodine, 2 parts potassium iodide, and 300 parts water.
After being washed with ethyl alcohol, the bacteria will either retain the strong blue colour of gentian violet or be completely decolourised. Sometimes a counterstain such as fuchsine or eosin is applied to give the decolourised bacteria a red colour to make them more visible.
Bacteria that retain the blue stain are known as gram-positive; those that do not are known as gram-negative. Organisms that sometimes retain the blue colour and sometimes do not are known as gram-variable.
The difference between Gram-positive and Gram-negative bacteria is in the permeability of the cell wall to these "purple collared iodine-dye complexes" when treated with the decolourising solvent.
Typical gram-positive bacteria are those staphylococci that produce boils; typical gram-negative bacteria are the bacilli that cause whooping cough; typical gram-variable bacteria are the bacilli that cause tuberculosis.
The best known and most widely used bacteriological staining method, it is almost always the first test performed for the identification of bacteria.
The primary stain of the Gram's method is crystal violet. Crystal violet is sometimes substituted with methylene blue, which is equally effective. Bacteria are first stained with the crystal violet and then treated with Lugol's solution, consisting of 1 part iodine, 2 parts potassium iodide, and 300 parts water.
After being washed with ethyl alcohol, the bacteria will either retain the strong blue colour of gentian violet or be completely decolourised. Sometimes a counterstain such as fuchsine or eosin is applied to give the decolourised bacteria a red colour to make them more visible.
Bacteria that retain the blue stain are known as gram-positive; those that do not are known as gram-negative. Organisms that sometimes retain the blue colour and sometimes do not are known as gram-variable.
The difference between Gram-positive and Gram-negative bacteria is in the permeability of the cell wall to these "purple collared iodine-dye complexes" when treated with the decolourising solvent.
Typical gram-positive bacteria are those staphylococci that produce boils; typical gram-negative bacteria are the bacilli that cause whooping cough; typical gram-variable bacteria are the bacilli that cause tuberculosis.
Reference:
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