How Is Endotoxin Tested


Lyophilized Amebocyte Lysate assay (TAL assay) is the most commonly used test for endotoxin. Tachypleus Amebocyte Lysate (TAL), is a kind of lyophilized product which mainly contains amoebocytes extracted from the blue blood of horseshoe crab.

LAL reacts with endotoxins, which is small bacterially-derived hydrophobic lipopolysaccharides (LPS) molecules locating in the outer cell membrane of gram-negative bacteria, to form a gel-clot which can be quantified. Endotoxin is measured in endotoxin units per millilitr (EU/mL).

Turbidimetric technique and chromogenic technique are also employed to detect endotoxins.

The reaction principle of chromogenic technique is that: the amebocyte lysate contains a cascade of serine protease enzymes (proenzymes) which can be activated by bacterial endotoxins. Endotoxins activate the proenzymes to produce activated enzymes (termed coagulase), the latter catalyzes the split of the colorless substrate, releasing a yellow-colored product pNA. The released pNA can be measured photometrically at 405nm. And the absorbance is positively correlated with the endotoxin concentration, then the endotoxin concentration could be quantified accordingly.

And the reaction principle of turbidimetric technique is similar with the one of chromogenic technique.

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