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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]
Medical microbiology, the large subset of microbiology that is applied to medicine, is a branch of medical science concerned with the prevention, diagnosis and treatment of infectious diseases. In addition, this field of science studies various clinical applications of microbes for the improvement of health.
Gram stain of cells from the vagina (the same magnification) with normal bacterial flora (top) and the bacteria that cause vaginosis (bottom). A variety of diagnosis techniques are currently available for identifying Gardnerella vaginalis such as the OSOM BV Blue assay, FemExam cards and nucleic acid amplification tests (NAATs), resulting in the determination of ongoing BV.
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 ...
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.
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 ...
Although L-forms can develop from Gram-positive as well as from Gram-negative bacteria, in a Gram stain test, the L-forms always colour Gram-negative, due to the lack of a cell wall. The cell wall is important for cell division, which, in most bacteria, occurs by binary fission.
Gram-negative bacteria will stain a pink color due to the thin layer of peptidoglycan. If a bacteria stains purple, due to the thick layer of peptidoglycan, the bacteria is a gram-positive bacteria. [4] In clinical microbiology numerous other staining techniques for particular organisms are used (acid fast bacterial stain for mycobacteria).