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A Gram stain of mixed Staphylococcus aureus (S. aureus ATCC 25923, gram-positive cocci, in purple) and Escherichia coli (E. coli ATCC 11775, gram-negative bacilli, in red), the most common Gram stain reference bacteria. Gram stain (Gram staining or Gram's method), is a method of staining used to classify bacterial species into two large groups ...
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Schematic of typical Gram-positive cell wall showing arrangement of N-Acetylglucosamine and N-Acetylmuramic acid; Teichoic acids not shown.. The Gram-positive cell wall is characterized by the presence of a very thick peptidoglycan layer, which is responsible for the retention of the crystal violet dyes during the Gram staining procedure.
Labeled diagram showing differences in the outer cell walls of Gram-positive and Gram-negative bacteria cell walls. British English A labelled diagram showing the differences in outercell layers between Gram-positive and Gram-negative bacteria.
Gram-positive cell walls are thick and the peptidoglycan (also known as murein) layer constitutes almost 95% of the cell wall in some Gram-positive bacteria and as little as 5-10% of the cell wall in Gram-negative bacteria. The peptidoglycan layer takes up the crystal violet dye and stains purple in the Gram stain.
Starch is a substance common to most plant cells and so a weak iodine solution will stain starch present in the cells. Iodine is one component in the staining technique known as Gram staining, used in microbiology. Used as a mordant in Gram's staining, iodine enhances the entrance of the dye through the pores present in the cell wall/membrane.
Aggregatibacter actinomycetemcomitans is a Gram-negative coccobacillus prevalent in subgingival plaques. Acinetobacter strains may grow on solid media as coccobacilli. Bordetella pertussis is a Gram-negative coccobacillus responsible for causing whooping cough. Yersinia pestis, the bacterium that causes plague, is also coccobacillus. [26]
The Gram stain, developed in 1884 by Hans Christian Gram, characterises bacteria based on the structural characteristics of their cell walls. [176] [77] The thick layers of peptidoglycan in the "Gram-positive" cell wall stain purple, while the thin "Gram-negative" cell wall appears pink. [176]