What is the difference between gram-positive bacteria and gram-negative bacteria?

Gram staining is a differential staining method widely used in bacteriology, which was founded by Danish doctor Gram in 1884. Bacteria were dyed with basic dyes, and decolorized with alcohol after mordant dyeing with iodine solution. Under certain conditions, some bacteria cannot be decolorized, while others can be removed. Therefore, bacteria can be divided into two categories, the former is called Gram-positive bacteria (G+) and the latter is called Gram-negative bacteria (G-). For the convenience of observation, after decoloration, red dyes such as basic saffron are used for re-dyeing. Positive bacteria are still purple, and negative bacteria are dyed red. Bacillus and most cocci, as well as all actinomycetes and fungi, are gram-positive. Vibrio, spirochete and most pathogenic bacilli are gram-negative reactions.

The differences between them are as follows: ① The composition of cell wall is different. The cell wall of Gram-positive bacteria contains a lot of peptidoglycan, phosphomuramic acid and no lipopolysaccharide. Gram-negative bacteria contain a small amount of peptidoglycan and lipopolysaccharide, and do not contain phosphomuramic acid. The difference between them lies in the different contents of various components, especially the fat content, which is 1% ~ 4% for Gram-positive bacteria and1%~ 22% for Gram-negative bacteria.

② Different cell wall structures. The cell wall of Gram-positive bacteria is thick, ranging from 20 to 80 nm, and its structure is simple. Gram-negative bacteria have a thin cell wall, 10nm, and a complex structure, which is divided into outer wall layer and inner wall layer. The outer wall layer is divided into three layers, the outermost layer is lipopolysaccharide, the middle layer is phospholipid, the inner layer is lipoprotein, and the inner wall layer contains peptidoglycan without phosphomuramic acid.