The different compositions of endotoxin can lead to three forms of bacterial phenotype, namely smooth type, rough type, and intermediate type (also called mucus type). When the core polysaccharide component is reduced or damaged, the appearance of bacterial culture colonies is rough, so it is called rough mutant (rough-LPS, R), which can be called Rb-LPS, Rc-LPS, Rd-LPS, Re-LPS according to the degree of the core polysaccharide defect, as shown in the figure.

The electron microscope of Escherichia coli LPS with smooth colonies is a slender cord-like structure, while the rough type of Escherichia coli LPS is mostly a circular structure. Due to the different lengths of its sugar chain, different steric hindrance effects will be produced, which will affect the recognition and phagocytosis of LPS and CNB by immune cells of the body, so that the host will have different immune effects on it and affect the clearance of bacteria by the body.

The rough type sugar chain is short and is easy to be swallowed by phagocytes, such as occupational phagocytes: neutrophils, and macrophages, which are easy to remove rough type bacteria; The smooth sugar chain is long, has steric hindrance, is not easy to be swallowed by phagocytes and combined with complement, and is easy to escape the immune response of the body to it.