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Gram stain (Gram staining or Gram's method), is a method of staining used to classify bacterial species into two large groups: gram-positive bacteria and gram-negative bacteria. It may also be used to diagnose a fungal infection . [ 1 ]
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 ...
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-negative cell wall contains a thinner peptidoglycan layer adjacent to the cytoplasmic membrane than the Gram-positive wall, which is responsible for the cell wall's inability to retain the crystal violet stain upon decolourisation with ethanol during Gram staining.
Radhey Gupta's molecular taxonomy, based on conserved signature sequences of proteins, includes a monophyletic Gram negative clade, a monophyletic Gram positive clade, and a polyphyletic Archeota derived from Gram positives. [65] [66] [67] Hori and Osawa's molecular analysis indicated a link between Metabacteria (=Archeota) and eukaryotes. [68]
Gram-negative bacteria are bacteria that, unlike gram-positive bacteria, do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. [1] Their defining characteristic is that their cell envelope consists of a thin peptidoglycan cell wall sandwiched between an inner ( cytoplasmic ) membrane and an outer ...
[4] [8] In contrast to gram-positive bacteria, all archetypical Gram-negative bacteria are bounded by a cytoplasmic membrane as well as an outer cell membrane; they contain only a thin layer of peptidoglycan (2–3 nm) between these membranes. The presence of both inner and outer cell membranes forms and define the periplasmic space or ...
Porins were first discovered in gram-negative bacteria, but gram-positive bacteria with both types of porins have been found. [9] They exhibit similar transport functions but have a more limited variety of porins, compared to the distribution found in gram-negative bacteria. [9]