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Pyrogens are fever-causing (inducing) agents that include toxins of microorganisms, especially toxins or components (such as lipopolysaccharides, LPS) of the cell wall of Gram negative bacteria. Pyrogen testis defined as a test that detects the presence of bacterial endotoxins (lipopolysaccharides in particular) in a given product or sample including food, air, parenteral drugs and other pharmaceutical or medical products and devices. Such tests form part of the aspects of the quality control of these pharmaceutical and food products; and it is critical to conduct pyrogen test on them prior to their release into the market for human or animal consumption.


Pyrogen testing can be carried out in two different ways which include:

  • In vitro pyrogen testing, and
  • In vivo pyrogen testing.

While the in vitro pyrogen testing is carried out outside a living system (i.e., in a test plate or card) using antigenic substances, the in vivo pyrogen testing is normally carried out in a living system such as in a laboratory mouse or rabbit. The Limulus Amoebocyte Lysate (LAL) test is a typical example of an in vitro pyrogen testing that is widely used for detecting the presence of pyrogens in parenteral drugs, food products and other medical and biopharmaceutical products including vaccines and water for injection.

Pyrogenicity is simply defined as the ability of a pyrogen to cause infection or disease in an animal or human host. Pyrogenicity usually occurs following the consumption or administration of a pyrogen-contaminated food or pharmaceutical product into the body of an animal or human host. The endotoxins of Gram negative bacteria consist of three different morphological regions (Figure 1). These regions include the:

  1. Lipid A (a lipid moiety) region,
  2. The polysaccharide core, and
  3. The O-(specific) antigenic side chains.
Figure 1. Illustration of Gram negative cell membrane. Toxicity is associated with the lipid component (Lipid A) and immunogenicity is associated with the polysaccharide components of the lipopolysaccharide (LPS) compartment of Gram negative bacteria. Photo courtesy:

The Lipid A region is linked to the polysaccharide core which in turn is linked to the O-(specific) antigenic side chains. Lipid A is the sole portion of the Gram negative bacterial cell wall that is responsible for the antigenic activity of LPS in the body of a human or animal host.

The functions of bacterial endotoxins in a human host include:

  • The induction of fever,
  • The production of cytokines and prostaglandins,
  • The induction of hypotensive shock, and
  • Cell death or death of the host.

To this day, parenteral drugs including vaccines, drugs (antibiotics), water for injection and even some food products are regularly tested for the presence of exogenous pyrogens – so that they can be confirmed as safe, hygienic and of good quality for human or animal consumption. Parenteral drugs and other medical/pharmaceutical products meant for systemic administration must be free from every form of microbial contamination and toxic/chemical substances capable of inducing fever (aside other medical conditions associated with pyrogens) in a human or animal host. And this is why the preparation and/or production processes for the production of parenteral products meant for medical/pharmaceutical usage is often carried out in sterile and/or aseptic conditions – so that the contamination of these products will be limited as much as possible.

Thus, all the processes involved in the production of food products and medical/pharmaceutical products intended for parenteral usage in target human populations must be designed and handled in such a way that they eliminate the contamination of the production processes and/or equipment and instruments by potential and harmful microorganisms. It is critical to measure and detect the presence of pyrogens from parenteral drugs including water for injections prior to their usage in order to prevent adverse effects associated with pyrogens in the end users. The presence of pyrogens in a product such as a parenteral drug can lead to fever, shock, hypotension (low blood pressure), organ failure and possibly death. Parenteral drugs including vaccines meant for systemic administration must be of a pyrogen-free quality before it can be certified safe for human consumption.

Further reading

Bushell M.E (1998). Application   of   the   principles   of   industrial   microbiology   to   biotechnology (ed. Wiseman, A.) Chapman and Hall, New York.

Byong H. Lee (2015). Fundamentals of Food Biotechnology. Second edition. Wiley-Blackwell, New Jersey, United States.

Frazier W.C, Westhoff D.C and Vanitha N.M (2014). Food Microbiology. Fifth edition. McGraw-Hill Education (India) Private Limited, New Delhi, India.

Jay J.M (2005). Modern Food Microbiology. Fourth edition. Chapman and Hall Inc, New York, USA.

Bushell M.E (1998). Application   of   the   principles   of   industrial   microbiology   to   biotechnology (ed. Wiseman, A.) Chapman and Hall, New York.

Farida A.A (2012). Dairy Microbiology. First edition. Random Publications. New Delhi, India.

Nduka Okafor (2007). Modern industrial microbiology and biotechnology. First edition. Science Publishers, New Hampshire, USA.

Roberts D and Greenwood M (2003). Practical Food Microbiology. Third edition. Blackwell publishing Inc, USA.

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