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Safranin (Safranin O or basic red 2) is a biological stain used in histology and cytology. Safranin is used as a counterstain in some staining protocols, colouring cell nuclei red. This is the classic counterstain in both Gram stains and endospore staining. It can also be used for the detection of cartilage, [2] mucin and mast cell granules.
Gram-positive bacteria have a thick mesh-like cell wall made of peptidoglycan (50–90% of cell envelope), and as a result are stained purple by crystal violet, whereas gram-negative bacteria have a thinner layer (10% of cell envelope), so do not retain the purple stain and are counter-stained pink by safranin. There are four basic steps of the ...
Crystal violet stains both Gram positive and Gram negative organisms. Treatment with alcohol removes the crystal violet colour from gram negative organisms only. Safranin as counterstain is used to colour the gram negative organisms that got decolorised by alcohol. While ex vivo, many cells continue to live and metabolize until they are "fixed".
Gram-positive bacteria have a thick peptidoglycan layer in their cell wall, which retains the crystal violet during Gram staining, resulting in a purple color. Gram-negative bacteria have a thin peptidoglycan layer which does not retain the crystal violet, so when safranin is added during the process, they stain red.
Depending on pH growth conditions, the peptidoglycan forms around 40 to 90% of the cell wall's dry weight of gram-positive bacteria but only around 10% of gram-negative strains. Thus, presence of high levels of peptidoglycan is the primary determinant of the characterisation of bacteria as gram-positive. [ 5 ]
One commonly recognizable use of differential staining is the Gram stain. Gram staining uses two dyes: Crystal violet and Fuchsin or Safranin (the counterstain) to differentiate between Gram-positive bacteria (large Peptidoglycan layer on outer surface of cell) and Gram-negative bacteria. Acid-fast stains are also differential stains.
Figure 1: A bi-phasic bacterial growth curve.. A growth curve is an empirical model of the evolution of a quantity over time. Growth curves are widely used in biology for quantities such as population size or biomass (in population ecology and demography, for population growth analysis), individual body height or biomass (in physiology, for growth analysis of individuals).
Cell growth refers to an increase in the total mass of a cell, including both cytoplasmic, nuclear and organelle volume. [1] Cell growth occurs when the overall rate of cellular biosynthesis (production of biomolecules or anabolism) is greater than the overall rate of cellular degradation (the destruction of biomolecules via the proteasome, lysosome or autophagy, or catabolism).