Gram-negative Bacteria vs. Gram-positive Bacteria

A special technique used to stain bacteria was developed by Christian Gram in 1884. The technique today is called Gram staining. The procedure involves using a dye called crystal violet and the bacteria is stained blue. They are then treated with an iodine solution and then decolorized with alcohol.

The bacteria are grouped into two categories based on this stain ability using the Gram staining procedure, as well as the basis of the cell wall structure. There are Gram-negative bacteria and Gram positive bacteria.

Gram-positive bacteria retain the color of the stain, and Gram-negative bacteria lose the color of the stain. There is retention of the color even after washing with alcohol or acetone with Gram-positive bacteria, but the Gram-negative does not retain the stain when washed with alcohol or acetone.

Of course, there are several other differences as well. For Gram-positive bacteria the outer membrane is absent and the cell wall is 20-30 nm thick. However, for Gram-negative bacteria there is an outer membrane and the cell wall is not as thick, just 8-12 nm thick.

Other differences in the bacteria are also related to the cell wall. In Gram-positive bacteria the cell wall contains 70 to 80% murein, opposed to just 10 to 20 % murein for the Gram-negative bacteria. The lipid content is also very low in the former, but in the latter, the lipid content is 20 to 30%.

The cell wall is smooth in the Gram-positive bacteria, but much different in the Gram-negative bacteria. In Gram-negative it is wavy, comes in contact with plasma membrane, though only in a few locations. In addition, the cell wall in Gram-positive bacteria contains teichoic acids, but none are present in the Gram-negative bacteria.

Furthermore, in Gram-positive bacteria the basal body of the flagellum contain just two rings, but for Gram negative bacteria there are twice as many rings contained in the basal body of the flagellum. The prominence of mesosomes are different between the bacterium. They are fairly prominent in Gram-positive, though less so in Gram-negative.

Finally, a few pathogenic bacteria belong to the Gram-positive group such as bacillus, nocardia, mycobacterium, mycoplasma, staphylococcus, streptococcus, listria, and a few others. These are more susceptible to antibiotics.

On the other hand, most of the pathogenic bacteria belong to the Gram-negative group such as Escherichia coli, otherwise known as E. coli. Other Gram-negative includes cyano bacteria, hemophilus, chlamydia, pseudomona, salmonella, Treponema, and many others. These are more resistant to antibiotics.

In summary, one of the most significant and noticeable differences between Gram-positive bacteria and Gram-negative bacteria is based on its stain ability, with Gram-positive retaining the color, and Gram-negative losing its color. Other differences include its resistance to antibiotics, cell wall size, and murein, lipid, and teichoic acid content.