Content Curator
Pathogens and bacteria are all around the world and produce toxins and enzymes which play a significant role in pathogenicity. These toxins participate to damage cells in order to trigger immune response and slow down cellular processes. Toxins range from minutely effective to deadly. There are two types of toxins: Exotoxins and Endotoxins.
Exotoxins are proteins that are produced inside pathogenic bacteria while endotoxins are lipid portions of lipopolysaccharides (LPSs).
Also Read: MCQs on Immunity
Key Terms: Endotoxins, Exotoxins, Cell, Bacteria, Cell membrane, Toxins, Proteins, Enzymes, Pathogens, Antibiotics
What are Exotoxins?
[Click Here for Sample Questions]
Exotoxins are heat-liable proteins and are secreted by certain species of bacteria that have been diffused in the surrounding medium. These are released outside the cell (extracellularly) as the organism develops and are contagious toxins. They spread from the
region of infection to other parts of the body causing damage.
Exotoxin Process
What are Endotoxins?
[Click Here for Sample Questions]
Endotoxins are lipopolysaccharide-protein complexes and are heat-stable. They form the essential components of the cell wall of Gram-Negative Bacteria and are liberated only on either cell lysis or the death of bacteria. They are secreted by a developing bacteria either because of some specific antibiotics or at the action of phagocytic digestion.
Also Read:
Differences between Exotoxins and Endotoxins
[Click Here for Sample Questions]
The key difference between exotoxins and endotoxins are briefed below.
| Basis | Exotoxins | Endotoxins |
|---|---|---|
| Chemical Nature | These are secreted by bacteria and are composed of proteins. | These are composed of a heteropolysaccharide and a lipid. |
| Enzymes Present | Enzymes present are: Hyaluronidase, Collagenase, Nuclease, etc. | Enzymes present are: Catalase, Fibrolysene and IgG proteases. |
| Source | These are secreted outside the cell by both, the gram-positive as well as gram-negative bacteria. | These are secreted by the cell membrane of gram-positive bacteria and are an integral part of the cell wall. |
| Location | Inside the cell | Outside the cell |
| Heat Stability | Heat-liable (around 600-800 C) | Heat-stable (around 2500 C) |
| Detection Test | Detected by ELISA-based methods and neutralization. | Detected by Limulus Lysate Assay test. |
| Toxicity | These are highly toxic. | These are moderately toxic. |
| Diseases | Cause diseases such as Diptheria, scarlet fever and diarrhoea. | Cause diseases such as urinary tract infection, coronary artery disease and typhoid fever. |
| Examples | Clostridium botulinum, Clostridium tetani, and Corynebacterium diphtheriae. | Salmonella typhi, Vibrio cholerae, and Streptococcus pneumoniae |
Things to Remember
- Endotoxins are lipid portions of lipopolysaccharides (LPSs) while exotoxins are proteins that are produced inside pathogenic bacteria.
- Exotoxins are released outside the cell and are highly contagious toxins.
- Endotoxins form the structural components of the cell wall of Gram-Negative Bacteria and are secreted by the cell membrane.
- Exotoxins are heat-liable while endotoxins are heat-stable.
Sample Questions
Ques: Name bacteria that produce endotoxins. [1 mark]
Ans: Some of the bacteria that produce endotoxins are E.coli, Salmonella, Pseudomonas, etc.
Ques: Name a few bacteria that produce exotoxins. [1 mark]
Ans: Some bacteria that produce exotoxins are Clostridium botulinum, Clostridium tetani, Corynebacterium diphtheriae, etc.
Ques: How do exotoxins and endotoxins cause infections? [1 mark]
Ans: The exotoxins release toxins immediately into the environment while the endotoxins release the toxins only when the bacteria have died.
Ques: Name a few exotoxins. [2 marks]
Ans: A few exotoxins are as follows:
- Saxitoxin
- Tetrodotoxin
- Eledoisin
- Conotoxin
Ques: Name a few endotoxins. [2 marks]
Ans: A few endotoxins are as follows:
- Salmonella typhi,
- Vibrio cholerae, and
- Streptococcus pneumoniae
Ques: How can the endotoxins be destroyed? [2 marks]
Ans: Endotoxins can be inactivated or destroyed when exposed at a temperature of 250º C for more than 30 minutes. They can also be destroyed through neutralization by acids and alkenes on a laboratory scale.
Ques: Can endotoxins be detected? [2 marks]
Ans: Yes, we can detect endotoxins through the rabbit pyrogen test which is the first standard technique for endotoxin detection. Nowadays the Limulus Amoebocyte Lysate test is the most popular detection technique for endotoxin.
Ques: Are all the exotoxins proteins? [2 marks]
Ans: Exotoxins are soluble proteins that enter host cells, catalysing the covalent modification of a host cell component(s) in order to alter the physiology. Both Gram-negative and Gram-positive bacteria produce exotoxins.
Ques: Where are the exotoxins found majorly? [1 mark]
Ans: For the most part, genes are involved in the production of exotoxins which can be found in plasmid or extrachromosomal DNA.
Also Check-Out::
Comments