• Sufia Sani

What is the Difference Between Bioburden and Endotoxin Test?

What is Bioburden Testing?


Bioburden is the population of viable microorganisms in or on a product, water, or raw material. Bioburden test determines the number of these microorganisms present, reported as colony forming units (CFU).


The test usually involves an extraction step to remove the microorganisms followed by an enumeration or culturing technique to quantify the extracted organisms.


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What is Bacterial Endotoxin Test?

Bacterial endotoxins are phospholipids called lipopolysaccharides (LPS) found in the outer membrane of gram-negative bacteria. LPS are not excreted by gram negative bacteria but are released after death and lysis of the bacterial cell. Therefore, endotoxins do not come from viable or live microorganisms.


Good examples of endotoxin producing gram- negative bacteria are Escherichia coli, Proteus, Pseudomonas, Enterobacter and Klebsiella. Bacterial endotoxin may be present in food, water or surfaces contaminated with gram negative bacteria.


Once endotoxin enters the blood stream or cerebrospinal fluid it triggers several different biological responses such as fever and inflammation followed by septic shock and death if not treated quickly.


Bacterial Endotoxin Test or Limulus Amebocyte Lysate Test (LAL test) is used to detect endotoxin in a substance or medical device. It is primarily used in blood products, pharmaceuticals, water purification, and other areas where it is important to test for the presence of endotoxin.


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What is the Difference Between Bioburden Test and Endotoxin Test?

Bioburden test quantifies viable or live microorganisms present on a medical device or product. Whereas bacterial endotoxin test detects, and estimates endotoxin produced by the death of gram-negative microorganisms (non-viable microorganisms).

Bioburden test is applicable to (according to ISO 11737-2:2018):

  • Validation and re-validation of sterilization processes

  • Routine monitoring for control of manufacturing processes

  • Monitoring of raw materials, components, or packaging

  • Assessment of the efficiency of cleaning processes

  • An overall environmental monitoring program


Endotoxin test is required for:

  • Sterile and nonpyrogenic assemblies or devices in contact directly or indirectly with the cardiovascular system, the lymphatic system, or cerebrospinal fluid. These requirements do not apply to orthopedic products, latex gloves, or wound dressings. (USP 161)

  • Products that have direct or indirect intravascular, intralymphatic, or intrathecal contact or have the potential for similar systemic exposure, or ophthalmic products for intraocular use. (AAMI ST 72:2011)


Since bioburden test requires a culturing and incubation step to revive extracted microorganisms, the test takes about 7 days to complete.


Endotoxin test extracts endotoxins present on a product or medical device and enumerates them by assaying using Limulus Amebocyte Lysate (LAL), either by gel clot method, kinetic turbidimetric method or chromogenic method. No culturing step is needed for bacterial endotoxin test therefore, the test can be completed within a day.


For medical devices, the endotoxin limit is 0.5 EU/mL or 20 EU/device for products that directly or indirectly contact the cardiovascular system and lymphatic system. For devices in contact with cerebrospinal fluid, the endotoxin limit is 0.06 EU/mL or 2.15 EU/device.

References

Bioburden Testing

  • ISO 11737-1:2018

  • USP <61>

  • USP <62>

Bacterial Endotoxin Testing

  • USP <85>

  • USP <161>

  • ISO 11737-3 Sterilization of health care products - Microbiological methods - Part 3: Bacterial endotoxin testing is under development.


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