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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]
The Nugent Score is a Gram stain scoring system for vaginal swabs to diagnose bacterial vaginosis (BV).The Nugent score is calculated by assessing for the presence of large Gram-positive rods (Lactobacillus morphotypes; decrease in Lactobacillus scored as 0 to 4), small Gram-variable rods (Gardnerella vaginalis morphotypes; scored as 0 to 4), and curved Gram-variable rods (Mobiluncus spp ...
Colonial morphology serves as the first step in the identification of microbial species from clinical samples. [10] Based on the visual appearance of the colonies, microbiologists can narrow down the list of possible organisms, allowing them to select appropriate tests to provide a definitive diagnosis.
Owing to their morphological properties, spirochetes are difficult to Gram-stain but may be visualized using dark field microscopy or Warthin–Starry stain. [35] Examples include: Leptospira species, which cause leptospirosis. Borrelia species, such as Borrelia burgdorferi, a tick-borne bacterium that causes Lyme disease
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 ...
Despite there being little agreement on the major subgroups of the Bacteria, Gram staining results were most commonly used as a classification tool. Consequently, until the advent of molecular phylogeny, the Kingdom Prokaryota was divided into four divisions, [ 41 ] A classification scheme still formally followed by Bergey's manual of ...
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.
Koser’s agar, developed by Stewart A. Koser in 1923, is a clear, colorless agar that allows the observation of bacterial growth by turbidity. [6] With a colorless agar, misinterpreting negative results as positives is more common, which can be reduced by Simmons’ modification of adding bromothymol blue.