Pyrogens and Bacterial Endotoxins

A pyrogen is a molecule that is fever-producing. Some bacteria produce pyrogens that are known as endotoxins and exotoxins. Endotoxins are found in the cell wall of Gram-negative bacteria and exotoxins are molecules that some bacteria make internally and secrete to the outside. Endotoxins and exotoxins are released when a bacterium lyses. Endotoxins come in lipopolysaccharide (LPS) form.

Any surface that has come in contact with bacteria has a potential for pyrogen contamination. How you store sterilized materials is another factor because improper storage may cause the development of pyrogens. Endotoxins tend to stick to glassware and are difficult to wash away with soap and water. Autoclaving can sterilize the surface of glassware, however, endotoxins that cling to sides tend to be too heat-resistant to be removed. They need to be exposed to high dry heat temperatures for an extended period of time (i.e. 250 °C for 30 minutes. It is believed that autoclaving and boiling doesn’t destroy all the endotoxin present. That is to say depyrogenation is more difficult than sterilization.

An article published in Applied Environmental Microbiology (August of 2009) reported a new soft hydrothermal process for depyrogenation that assures complete denaturization of endotoxin. The soft hydrothermal process was run at 130 °C for 60 min or at 140 °C for 30 min in the presence of a high steam saturation ratio or with a flow system. They also demonstrated that water could be purified at the same temperature and times without requiring further ultrafiltration or the use of an anion exchanger. This high steam saturation process works well for parenterals and medical devices that can’t withstand the high temperatures of dry heat treatments.

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For more information on soft hydrothermal processing:

Inactivation of Escherichia coli Endotoxin by Soft Hydrothermal Processing