Gram Positive Bacteria

Custom Student Mr. Teacher ENG 1001-04 13 January 2017

Gram Positive Bacteria

The core difference between a gram positive bacteria and gram negative bacteria is the differences in cell wall composition. Prokaryotes known as eubacteria have three basic forms: rods, cocci and spiral. The bacterial cell wall is the single most important contributor to cell shape. In addition to shape of cell wall, presence or absence of flagellum, and if present, positions of flagellum, the eubacteria can be classified according to Gram Stain. First and foremost, gram positive bacteria are by and large dark, blue and dark purple shades when they endure a process of straining. Their basic features are examined on the basis of their cytoplasmic lipid membrane, cell wall, and finally the presence of the bacteria in the cystol. Gram positive bacteria are mainly composed of a capsule polysaccharide, thick peptidoglycan layer, and flagellum which are present in certain species. It can either be aerobic or anaerobic. Gram positive bacteria have a simpler cell wall, with a large amount of peptidoglycan.

Peptidoglycan is a polymer composed of modified sugars cross-linked by short polypeptides. In effect, the cell wall traps the crystal violet in the cytoplasm, concealing the red dye safranin in gram staining experiment. Certain gram positive species have virulent strains that are resistant to one or more drugs. Gram negative bacteria on the other hand are composed of lipopolysaccharides (LPS), porin channels, and murein lipoprotein which is all absent in gram positive bacteria. Their cell wall has less peptidoglycan, but is structurally more complex, with the outer layer composed of lipopolysaccharides. Their cell wall is located between two layers of plasma membrane. Crystal violet in gram negative bacteria is easily rinsed off from the cytoplasm, and the cell appears to be pink or red due to the thin layer of the cell wall. LPS in gram negative bacteria tends to be toxic, causing shock and fever.

Gram negative bacteria also tend to be more resistant to antibiotics due to its outer membrane which inhibits drugs from entry. A biochemical test that can be used to distinguish between gram positive and gram negative is gram staining, which was developed by Hans Christian Gram developed a staining technique that grouped bacteria according to their cell wall structure. When conducting the experiment, a bacterial smear is dried out. Heat is thenceforth applied to cause it to cleave unto the glass slide. Next, a few drops of crystal violet dye is then spread out unto the smear surface, for not more than 30 seconds. Water is then used to rinse it out until its droplets’ falling out the slide appears to be colorless. Iodine is afterwards added unto the smear following by rinsing it off by water. Iodine acts as a mordant, in other words it binds the dye to the cell. The smear at that juncture is decolorized by alcohol and counterstained by safranin. This is the essential portion of the test owing to the fact that too much or too little can alter the results of the experiment. In gram positive bacteria, as stated earlier remains purple when observed under the microscope.

The retention of the crystal violet die due to the bacteria’s thick cell wall is the primary contributor to its color. On the other hand, gram negative bacteria displayed a colorless cell; however a red color emerged as a result of safranin. These are the elementary steps in distinguishing between the two groupings of bacteria and it is often executed in a hospital laboratory, to identify which of the two categories of bacteria is causing a particular disease. In conclusion, the morphological differences between the two groupings of bacteria species are centered on the layers of peptidoglycan layers. Gram stain test can be used to easily distinguish between a gram positive and gram negative bacteria which are based on the color they intend to appear.


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  • University/College: University of Chicago

  • Type of paper: Thesis/Dissertation Chapter

  • Date: 13 January 2017

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