Bacterial Endotoxin Detection by Chromogenic Method: Introduction, Principle, Product Characteristics, and Keynotes

Introduction of Bacterial Endotoxin Detection by Chromogenic Method

Bacterial Endotoxin Detection by Chromogenic Method uses for screening and diagnosis of Gram-negative bacterial infection with a low limit of detection is 1 pg/ml (0.005EU/ml). It also applies to the quantitative detection of endotoxin in pharmaceutical and biological end-products. The low limit of detection is 0.001EU/ml. Endotoxin is heat stable lipopolysaccharide (LPS)-protein complexes that form structural components in Gram-Negative Bacterial cell walls and it is liberated only on cell lysis or death of bacteria.

Principle of Chromogenic Method

In brief, a key principle of the chromogenic method is to reveal the presence of the analyte in a test specimen through chemically-induced visible color changes. The resulting color is then recorded by applying spectrophotometric methods to reveal the concentration of the analyte in the test sample.

Product Characteristics

Method	Chromogenic	Chromogenic
Sample	serum	Dialysate, dialysis water
Detection object	Gram-Negative Bacteria	Pyrogen material
Detection time	1 hour	40 minutes
Low detection limit	1 pg/ml (0.005EU/ml)	0.001EU/ml
Machine to operate on	Goldstream kinetic tube reader	Microplate reader

Keynotes on Endotoxin

• Endotoxin can be detected other than chromogenic methods are gel-clot and turbidimetric methods.
• A chromogenic method is of two types- Kinetic and end-point chromogenic methods.

Features of Endotoxins

• Endotoxins are lipopolysaccharide of molecular weight 50KDa-1000KDa.
• They are found mostly in Gram-negative bacteria.
• They form an integral part of the cell wall; released only on disruption of the bacterial cells.
• Heat stable
• They are comparatively weakly antigenic. Anatoxins are not formed but antibodies against polysaccharides are raised.
• Toxoids can not be made.
• No enzymic action
• They express low potency.
• They are usually pyrogenic and feverish by induction of interleukin 1 (IL-1) production.
• Lacking specific receptor
• Not filterable
• On boiling they don’t get denatured.
• They are located on chromosomal genes.
• They are detected by Limulus lysate assay.
• Some endotoxins-produced bacteria are Escherichia coli, Salmonella enterica serotype Typhi, Shigella, and Vibrio cholerae.
• Diseases caused by endotoxins-producing bacteria are meningococcemia, and sepsis by Gram-negative rods (GNRs).

Further Reading

1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5793131/
2. https://textbookofbacteriology.net/endotoxin.html
3. https://www.pharmtech.com/view/comparing-endotoxin-detection-methods
4. https://www.era-bio.com/article-4675-5877.html
5. Jawetz, Melnick and Adelberg’s Medical Microbiology. Editors: Geo. F. Brook, Janet S. Butel & Stephen A. Morse, 21st ed 1998, Publisher Appleton & Lance, Co Stamford Connecticut.
6. Mackie and Mc Cartney Practical Medical Microbiology. Editors: J.G. Colle, A.G. Fraser, B.P. Marmion, A. Simmous, 4th ed, Publisher Churchill Living Stone, New York, Melborne, Sans Franscisco 1996.