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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]
A Gram stain is performed to show Gram-positive cocci in chains. Then, the organism is cultured on blood agar . The rapid pyrrolidonyl arylamidase (PYR) test is commonly used, wherein a positive reaction confers a presumptive identification of group A beta-hemolytic streptococci if the appearance and clinical context is consistent.
The encapsulated, Gram-positive, coccoid bacteria have a distinctive morphology on Gram stain, lancet-shaped diplococci. They have a polysaccharide capsule that acts as a virulence factor for the organism; more than 100 different serotypes are known, and these types differ in virulence , prevalence , and extent of drug resistance .
In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall. The Gram stain is used by microbiologists to place bacteria into two main categories, Gram-positive (+) and Gram ...
It is Gram-positive by Gram staining, but Mycobacterium leprae was traditionally stained with carbol fuchsin in the Ziehl–Neelsen stain. Because the bacilli are less acid-fast than Mycobacterium tuberculosis (MTB), the Fite-Faraco staining method, which has a lower acid concentration, is used now. [9] [10] In size and shape, it closely ...
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.
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]
Prolonged incubation (up to six weeks) may be required, as they are slow-growing, but on modern automated machines, the cultures often show positive results within 7 days. On Gram stain, they appear as dense clumps of Gram-negative coccobacilli and are exceedingly difficult to see. In recent years, molecular diagnostic techniques based on the ...