Endotoxins are an integral component of the outer membrane of the cell wall of Gram-negative bacteria, such as E.coli, Salmonella and Pseudomonas.  These are introduced into the environment upon cell death, and also in small amounts as part of normal cell physiological activity. Endotoxins consist of a polysaccharide and lipid complex with cell membrane fragments.  The polysaccharide component determines its antigenic properties; the lipid A component determines its biological activity. 

Endotoxins are exogenous pyrogens and tend to induce a rise in body temperature when introduced into blood or cerebrospinal fluid.  Common effects are fever and nausea, however in more extreme cases it can manifest as septic shock.

Endotoxins are naturally very heat stable, requiring extended exposure to temperatures in excess of 250°C to remove.

Bacterial Endotoxin Testing

Detection of bacterial endotoxins

Limulus Amebocyte Lysate (LAL) is an aqueous extract of the blood cells (amebocytes) from the Horseshoe Crab Limulus polyphemus.  The blood cells contain an enzyme system that is activated by contact with endotoxins or Gram-negative bacteria which causes a coagulation reaction.  This reaction is the basis of the LAL test methodologies; gel clot and kinetic.

The kinetic assay is the most sensitive of the method. RSSL can screen for the presence of endotoxins in:

  • Human drugs
  • Biologics
  • Animal drugs
  • Medical devices
  • Raw materials

Quantitative Endotoxin Testing

RSSL can provide quantitative endotoxin testing using Kinetic Turbidimetric or Kinetic Chromogenic assays.  Test samples are mixed with a reagent and measured for an increase in optical density (Turbidimetric) or colour change (Chromogenic).  The rate of change is used to determine the endotoxin levels calculated from a reference standard curve (linear regression).


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