Source

• Unlike exotoxins, which are secreted by bacteria, endotoxins are found within the cell. Endotoxins are commonly associated with Gram-negative bacteria and can be found within the outer membrane. These toxins were discovered by scientists when they realized that Gram-negative bacteria themselves were toxic. On the other hand, exotoxins are excreted into the surrounding medium by bacteria, fungi, algae and protozoa.
  
  

Structure

• A common example of an endotoxin includes lipopolysaccharide (LPS), found in the outer membrane of Gram-negative bacteria. The lipid portion of the molecule creates the inherent toxicity. Exotoxins are usually proteins that function directly with host cells to generate an effect. These structures can be secreted by bacteria or released into the surrounding medium through cell lysis.
  
  

Mechanism

• Unlike exotoxins, endotoxins do not act through an enzyme, resulting in lower potency levels and specificity. Because endotoxins are found structurally in the bacterial outer membrane, cell lysis is the most common way to release endotoxins. Once released, endotoxins function in close proximity with areas of bacterial presence. Exotoxins use intermediary enzymes to stimulate a range of host cell responses; these toxins usually attack tissue sites.
  
  

Consequences

• Both endotoxins and exotoxins are present during bacterial infections. Clinically, endotoxins cause severe inflammation to any contaminated tissue. Inhalation of endotoxins induces fever and airway constriction -- however, there is no antigenic response. Exotoxins are some of the most potent poisons available, and can have lethal consequences. Because there are so many different strains of exotoxins, the health hazards incorporate a diverse spectrum. Most notably, several exotoxins are so destructive that they can kill the host, before its immune system can fight back.