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Gram Stain

Page history last edited by lebrand-schmitz 14 years, 2 months ago

     Gram Staining was first discovered by the Danish bacteriologist Hans Christian Gram in 1882. Gram-Positive bacteria have a higher peptidoglycan count and a lower lipid count than Gram-Negative bacteria. 

     Peptidoglycans are composed of sugars and amino acids, and they form a membrane around a bacteria.    

Gram Staining is a way of identifying an unknown bacteria. Gram Staining is probably the most commonly used test to identify bacteria. There are multiple steps in performing a gram stain, which takes about twenty minutes. 

     First, a rack must be put over a staining tray or sink. This rack must have a slide with a smear placed on top of it as well. Then, one drop of crystal violet is paced on the smear for twenty seconds before the excess crystal violet is rinsed off with water. The now purple smear will have one drop of Gram's iodine placed on it for one minute. Afterwards, the excess Gram's iodine must be rinsed off with water. Multiple drops of decolorizing solution (95% ethanol) must be placed on the slide at a 45 degree angle until it is compleatly decolorized. The decolorizing agent is then rinsed off immediately. The smear is then covered with saffranin for one minute before being rinsed off. Finally, the slide is blotted off and then identified under a microscope. If the bacteria is Gram-Positive, it will be purple, and if it is Gram-Negative, it will be pink.

     Lactobacillus Thermophilus is a Gram-Postitive bacteria, which is sometimes negative in milk cultures. Image of Gram Stain above.

 

 

 

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