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Gram-positive bacteria have a thick mesh-like cell wall made of peptidoglycan (50–90% of cell envelope), and as a result are stained purple by crystal violet, whereas gram-negative bacteria have a thinner layer (10% of cell envelope), so do not retain the purple stain and are counter-stained pink by safranin. There are four basic steps of the ...
Gram-positive bacteria take up the crystal violet stain used in the test, and then appear to be purple-coloured when seen through an optical microscope. This is because the thick layer of peptidoglycan in the bacterial cell wall retains the stain after it is washed away from the rest of the sample, in the decolorization stage of the test.
However, it acquired an important practical use with the advent of serum therapy to treat certain types of pneumococcal pneumonia in the 1920s because selection of the proper antiserum to treat an individual patient required correct identification of the infecting pneumococcal serotype, and the quellung reaction was the only method available to ...
The Journal of Bacteriology is a monthly peer-reviewed scientific journal established in 1916. It is published by the American Society for Microbiology and the editor in chief is George A. O'Toole Jr. ( Dartmouth College ).
The inoculated plates are incubated at 37 °C for 24–48 hours to establish colonies. Fresh bacterial preparations should be used. After colonies have grown on the medium, 2-3 drops of the reagent DMPD are added to the surface of each organism to be tested. A positive test (OX+) will result in a color change violet to purple, within 10–30 ...
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] Cells are curved rod-shaped and are often seen wrapped together, due to the presence of fatty acids in the cell wall that stick together. [11]
A GBD study estimated the global death rates from (33) bacterial pathogens, finding such infections contributed to one in 8 deaths (or ~7.7 million deaths), which could make it the second largest cause of death globally in 2019. [6] [3] Most pathogenic bacteria can be grown in cultures and identified by Gram stain and other methods.
Bacteriophages introduce a gene into the bacterial cells that makes a strain toxigenic. The strains that are not infected with these viruses are harmless. [5] C. diphtheriae is a rod-shaped, Gram-positive, non spore-forming, and nonmotile bacterium. [17] C. diphtheriae has shown to exclusively infect humans. It is believed that humans may be ...