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Consequently, the need to identify human pathogens was a major impetus for the development of techniques to identify bacteria. [ 177 ] The Gram stain , developed in 1884 by Hans Christian Gram , characterises bacteria based on the structural characteristics of their cell walls.
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 ...
The manual was published subsequent to Bergey's Manual of Determinative Bacteriology, though the latter is still published as a guide for identifying unknown bacteria. [1] First published in 1923 by David Hendricks Bergey , it is used to classify bacteria based on their structural and functional attributes by arranging them into specific ...
Spiral bacteria are another major bacterial cell morphology. [2] [30] [31] [32] Spiral bacteria can be sub-classified as spirilla, spirochetes, or vibrios based on the number of twists per cell, cell thickness, cell flexibility, and motility. [33] Bacteria are known to evolve specific traits to survive in their ideal environment. [34]
Pathogenic bacteria are bacteria that can cause disease. [1] This article focuses on the bacteria that are pathogenic to humans. Most species of bacteria are harmless and many are beneficial but others can cause infectious diseases. The number of these pathogenic species in humans is estimated to be fewer than a hundred. [2]
One prominent scientist who opposes the three domain system is Thomas Cavalier-Smith, who proposed that the Archaea and the Eukaryotes (the Neomura) stem from Gram positive bacteria (Posibacteria), which in turn derive from gram negative bacteria (Negibacteria) based on several logical arguments, [57] [58] which are highly controversial and ...