5+Endotoxin bacteria examples : Detailed explanation

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In this post you will find the endotoxin bacteria examples and their detailed explanation.

Endotoxin refers to lipopolysaccharide which are integral part of the outer membrane of the gram-negative bacteria  and made up of hydrophobic component called Lipid A (disaccharide+ fatty acids) which is actually responsible for the toxicity and bioactivity of the endotoxin.

Examples of some gram positive and gram negative bacteria which secretes toxins

Diptheria toxin (Corynebacterium diptheriae)

Diptheria toxin is consist of two molecules, A molecule is effector portion that actually has an effect on the host cell and B is the receptor binding component. Diptheria toxin blocks cell protein synthesis and kills the host cell.

Cholera toxin (Vibrio cholerae)–

Cholera toxin (Vibrio cholerae) is composed of single A subunit and 5B subunits. This toxin elevates intracellular cyclic adenosine monophosphate in the epithelium of the small intestine and that causes movement of fluid into the lumen and the classic diarrhea associated with cholera.

Anthrax toxin (Bacillus anthrax)

Anthrax toxin (Bacillus anthrax) is highly lethal toxin composed to 2A and a B subunit which binds to the cell receptor.

Botulinum and Tetanus

Botulinum (Clostridium botulinum) and Tetanus (Clostridium tetani) toxins are neurotoxins. These toxins are elaborated by the bacteria at different sites make their way through the circulatory system and the lymph system to the brain where they cause their effect. Tetanus toxins causes muscles to contract uncontrollably and cause paralysis. On the other hand botulinum toxin blocks muscle contractions so the muscle get flaccid. These two toxins have very different effects on the central nervous system.  

Pseudomonas aeruginosa

Pseudomonas aeruginosa secretes exotoxin A which blocks the protein synthesis of  the host cells, follows quite same mechanism of diptheria toxin. This toxin is released as a proenzyme having low enzymatic activity but highly toxic to the animal cells. It enters the host cell through receptor mediated endocytosis.  

Microorganisms are ubiquitous in nature. Generally, bacteria are classified into two categories based on their Gram stain type : Gram positive and Gram negative ones. Gram positive bacteria are those having thick peptidoglycan while gram negative bacteria posses thin peptidoglycan.

List of Endotoxin bacteria

  • Escherichia coli
  • Salmonella
  • Shigella
  • Vibrio cholerae
  • Haemophilus influenza
  • Neisseria
  • Brucella pertussis

Frequently Asked Questions-

What is the main reason for the pathogenicity of gram-negative bacteria?

Gram-negative bacteria are mostly pathogenic in nature due to the presence of lipopolysaccharide (LPS) complex or lipoglycans on the outer membrane of most of the gram negative bacteria like Escherichia coli, Shigella, Salmonella, Neisseria, Haemophilus influenza etc.

The term endotoxin is generally associated with gram negative bacteria whether the bacteria is pathogenic in nature or not. LPS act as protective barrier for the bacterium to restrict the entry of bile salts, antibiotics, detergents and other toxic substance which can destroy the bacterium.

Components of Lipopolysaccharides (LPS)

Lipopolysaccharides (LPS) or Endotoxin are mainly consist of three parts:

  1. Lipid A
  2. Core polysaccharide
  3. O antigen
endotoxin bacteria examples
Structure of Lipopolysaccharide from Wikipedia

Lipid A is made up of two two sugar derivatives of glucosamine attached with fatty acids. Out of fatty acids, one of the fatty acid is myristic acid and these are unique to endotoxin. Polysaccharide is consist of ten sugars attached to Lipid A. O antigen is also called O side chain which helps to trigger the immune response by an affected host. This response will generate antibodies which will bind to the specific LPS. Lipid A and core polysaccharide are vertical to the outer membrane while O antigen is quite bent in structure.

Which part of  LPS is responsible for toxicity ?

Lipid A is responsible for endotoxin shock and is one of the main cause of death but it is weakly immunogenic even though it is highly pathogenic. Lipid A is same in all gram negative bacteria which is responsible for toxicity but polysaccharide is highly immunogenic and varies from one gram negative bacteria to another even if they are of same group with different strains.

Many bacteria can rapidly change the structure of O side chain and thus opposing the host defense mechanism.

Only Gram-negative bacteria can produce endotoxins? 

Endotoxins are not usually secreted or released by the bacteria, they are mainly released when gram negative bacteria goes disintegration. While gram-positive bacteria secretes only exotoxin.

Some species of gram-negative bacteria secretes exotoxin as well. Bordetella pertussis, Vibrio cholerae and Pseudomonas aeruginosa are the examples of gram negative bacteria which secretes exotoxins.

Which part of LPS is conserved in gram-negative bacteria?

The structure of lipid A is highly conserved in gram-negative bacteria. While core oligosaccharide shows variable structure among different species so that they can express uniquely modified types of endotoxin. O antigen shows high variability in LPS between different strains of same species.

How it works?

LPS  is recognized by pattern recognition receptor located on the surface of eukaryotic cell. We all have such receptors in order to recognize what is foreign particle to us. As a result, there is a production of cytokines which mobilize the immune response but may also have detrimental properties. Endotoxin secreted in small amounts have variety of effects, many of which reflect the attempts at the immune system of eliminating the bacterial infection.

For example: At low concentration, the endotoxin targets Kupffer cells of macrophages, it releases some cytokines (IL-1 and TNF) when it binds to its receptor and in effect it causes fever so endotoxin is well known to be pyrogenic fever inducing.

Endotoxin also activates B lymphocytes which produces antibodies and these are useful for clearing the illness.

In contrast, at very high levels of endotoxin, it often can result in shock, fluid loss due to release of many cytokines and disseminated intravascular clotting or coagulation.

The other membrane damaging toxins are lipases, an example is lecithinases from Clostridium species, this enzyme can lyse cells and eliminates defenses and provides nutrients for bacteria. Hemolysins can lyse red and white blood cells and there are toxins which forms pores in the cell membrane. They insert into the membrane allows water to flow in and the cell burst. These all are toxins which are used by bacteria to avoid immune defense of the host.

Effects of endotoxin in human body

The translocation of endotoxin play an important role in development of shock when accumulated in tissues and its bio-activities remained in tissues for long time.

Endotoxin can cause several kinds of effects in host body :

  1. Fever – Macrophages releases IL-1 and IL-6 when encounters endotoxin and further act on the hypothalamus which is a temperature regulatory centre.
  2. Hypotension – Shock and impaired perfusion of essential organs due to nitric oxide which induce vasodilation.
  3. Hypoglycemia – LPS in our body forces to metabolize the glucose faster into pyruvate by glycolysis. So the total concentration of the glucose in our body reduces.
  4. Disseminated intravascular coagulation (DIC) – Activation of tissue factor released from the damaged endothelial cells by endotoxin results  blood clot in our blood vessel and causes tissue Ischemia.

Click to read more on 22+ Non motile Bacteria Examples.

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