What does endotoxin mean?
An endotoxin is a poisonous substance built into the outer membrane of certain bacteria — specifically Gram-negative organisms such as E. coli and Salmonella. Chemically, it is a lipopolysaccharide: a large molecule combining lipid and sugar components. Unlike exotoxins, which living bacteria actively secrete, endotoxins are released mainly when bacterial cells die and break apart. Even then, their effects are potent: once in the bloodstream, endotoxin provokes the immune system to release inflammatory chemicals, producing fever, a drop in blood pressure, and in severe cases the life-threatening cascade of septic shock. The term matters well beyond medicine, because endotoxin is remarkably resistant to heat and standard sterilization, so drug and device makers must run dedicated tests — most famously the bacterial endotoxin test using horseshoe crab blood — to certify their products are free of it. Endotoxin is a formal scientific term, rarely used casually, but central to microbiology, hospital care, and pharmaceutical safety.
nounA toxic substance released from the outer membrane of certain Gram-negative bacteria, especially when the bacterial cell disintegrates; chemically a lipopolysaccharide.
- A heat-stable lipopolysaccharide toxin found in the outer membrane of Gram-negative bacteria, released upon cell lysis and capable of triggering strong immune responses such as fever and inflammation.
"The laboratory confirmed that the feverish reaction was caused by bacterial endotoxin in the intravenous fluid."
"Pharmaceutical manufacturers must demonstrate that their injectable products are free of detectable endotoxin."
"In patients with septicemia, circulating endotoxin can trigger the overwhelming inflammatory response known as septic shock."
Both the singular (as an uncountable substance) and plural (counting distinct molecules or types) forms are standard in scientific writing.
"Different Gram-negative species produce structurally distinct endotoxins."
Unlike many poisons that can be destroyed by heat, endotoxins are so sturdy they survive boiling and autoclaving — only specialized high-temperature depyrogenation removes them from medical equipment.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of endotoxin
Endotoxin combines the Greek-derived prefix endo-, meaning "within" or "inner," with toxin, a word of Greek origin (from toxikon, "poison for arrows") that entered modern scientific Latin in the nineteenth century. The term was coined in the late nineteenth century by bacteriologists who observed that some bacteria harbored a poison inside the cell itself, in contrast to the secreted exotoxins described at around the same time. It shares its endo- root with words like endoderm, endocrine, and endogamy, all conveying the idea of interiority.
Related word forms
How endotoxin is actually used
Endotoxin is a technical term used chiefly in microbiology, immunology, pharmacology, and medicine. It appears almost exclusively in formal or scientific writing rather than everyday conversation. The term is often encountered alongside its chemical name, lipopolysaccharide (LPS), and in quality-control contexts such as the Limulus amebocyte lysate (LAL) assay used to test medical products for endotoxin contamination.
Easily confused with endotoxin
An endotoxin is a lipopolysaccharide bound in the outer membrane of Gram-negative bacteria and released when cells break down, whereas an exotoxin is a protein actively secreted by bacteria (Gram-positive or Gram-negative) into their surroundings.