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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 ...
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.
In Berlin, in 1884, Gram developed a method for distinguishing between two major classes of bacteria. [1] This technique, known as Gram staining, continues to be a standard procedure of medical microbiology. This work gained Gram an international reputation. The staining method later played a major role in classifying bacteria. Gram was a ...
A major milestone in medical microbiology is the Gram stain. In 1884 Hans Christian Gram developed the method of staining bacteria to make them more visible and differentiated under a microscope. This technique is widely used today. [8]
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.
Both gram-positive and gram-negative bacteria commonly have a surface layer called an S-layer. In gram-positive bacteria, the S-layer is attached to the peptidoglycan layer. Gram-negative bacteria's S-layer is attached directly to the outer membrane. Specific to gram-positive bacteria is the presence of teichoic acids in the cell wall. Some of ...
EMB is often used to confirm the presence of coliforms in a sample. It contains two dyes, eosin and methylene blue in the ratio of 6:1. EMB is a differential microbiological media, which inhibits the growth of Gram-positive bacteria and differentiates bacteria that ferment lactose (e.g., E. coli) from those that do not (e.g., Salmonella ...
The principle behind this test is to use enzymes native to the organism to create a colored product in the presence of foreign molecules. The chemical 5-bromo-4-chloro-3-indolyl-beta-D-galactoside is used in the test because N. lactamica can hydrolyze it with the production of β- galactosidase , turning the solution into a blue color.