Question

What does LPS stand for, in what Gram type of bacteria is it found and where, and what is it composed of?

Answer 1

LPS - Lipopolysaccharide

It is also known as lipoglycans.

• It is a large molecule consist of a lipid and a polysaccharide with 0-antigen.
• Its outer and inner cores are joined by a covalent bond.
• Lipopolysaccharide is found in the outer membrane of Gram negative bacteria. It helps in the structural integrity of the bacteria.

COMPOSITION

LPS composed of three parts:

1. 0- antigen
2. Core oligosaccharide
3. Lipid A

O- antigen

• It is a glycan polymer within an LPS.
• Also reffered as 0 polysaccharide or 0 side chain of the bacteria.
• O antigen is attached to the core oligosaccharide & it comprises the outermost domain of the LPS molecule.
• This side chain may varies from strain to strain.
• Presence of this chain determines whether the LPS is considered rough or smooth ie, presence makes LPS as smooth and absence or reduction makes LPS rough.
• O antigen is exposed on the outer surface of the bacterial cell.

Core

• Core domain always contains an oligosaccharide component.
• This oligosaccharide component helps the core domain to attach directly to Lipid A. It contains sugars such as heptose.
• LPS cores of many bacteria also contain non carbohydrate components such as phosphate, amino acids and ethanol amine.

Lipid A

• It is a phosphorylated glucosamine disachharide with multiple fatty acids.
• It anchors the LPS into the bacterial membrane.
• Lipid A domain is responsible for the toxicity of the Gram negative bacteria.
• When the bacteria cells are lysed by the immune system, fragments of the membrane containing lipid A are released into the circulation causing diarrhoea, fever etc.
• Lipid A is a conserved component of LPS.
• Lipid A determines or defines the overall host immune activation and also it differs among bacterial species.