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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] The name comes from the Danish bacteriologist Hans Christian Gram, who developed the technique in 1884. [2]
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 ...
Other bacteria are commonly identified with a microscope by staining them with Gram stain. However, the mycolic acid in the cell wall of M. tuberculosis does not absorb the stain. Instead, acid-fast stains such as Ziehl–Neelsen stain, or fluorescent stains such as auramine are used. [4]
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 ...
A Gram stain of a urethral exudate showing typical intracellular Gram-negative diplococci, which is diagnostic for gonococcal urethritis [17]. Neisseria species are fastidious, Gram-negative cocci (though some species are rod-shaped and occur in pairs or short chains) that require nutrient supplementation to grow in laboratory cultures. [18]
A Ziehl–Neelsen stain is an acid-fast stain used to stain species of Mycobacterium tuberculosis that do not stain with the standard laboratory staining procedures such as Gram staining. This stain is performed through the use of both red coloured carbol fuchsin that stains the bacteria and a counter stain such as methylene blue .
The Ziehl-Neelsen stain is a two step staining process. In the first step, the tissue is stained with a basic fuchsin solution, which stains all cells pink. In the second step, the tissue is incubated in an acid alcohol solution, which decolorizes all cells except for acid-fast cells, which retain the color and appeared as red.
Fungal yeast forms are inconsistently stained with Acid-fast stain which is considered a narrow spectrum stain for fungi. [21] In a study on acid-fastness of fungi, [ 22 ] 60% of blastomyces and 47% of histoplasma showed positive cytoplasmic staining of the yeast-like cells, and Cryptococcus or candida did not stain, and very rare staining was ...