When a microorganism starts to synthesize toxin, they are called microbial toxins, such as bacteria and fungi. There are few bacteria that can produce the most potent natural toxins such as Botulinum neurotoxins.

However, the bacterial toxin has some medical importance that is why they are used in medical science and research.

What Is Toxin?

The toxin is a poisonous substance produced within microorganisms or other living cells. The term was first used by an organic chemist Ludwig Brieger from the word “toxic”. Toxins can cause disease or infection by damaging the host cell tissue.

What Is Bacterial Toxin?

There are few bacteria that can produce toxins, which is known as a bacterial toxin. Bacterial toxins are the virulence components that manipulate host cell features and take over the management of significant processes of residing organisms to favor microbial infection. Some toxins instantly goal innate immune cells, thereby annihilating a serious department of the host immune response. Some bacterial toxins are used for the treatment of tumors.

Toxigenesis, or the flexibility to supply toxins, is an underlying mechanism by which many bacterial pathogens produce illness.

Types of Bacterial Toxin

Bacterial toxin is divided into two classes such as;

1. Exotoxin
2. Enterotoxin

Bacterial Exotoxin

Exotoxins are proteins that are produced and released extracellularly by gram-positive and gram-negative bacteria.

Exotoxins are soluble, heat-labile proteins, which are mainly produced in the surrounding environment where bacteria grow. exotoxin can be inactivated at 60 to 80-degree centigrade temperature.

Example: Botulism, gas gangrene, tetanus, diphtheria, staphylococcal food poisoning, cholera, enterotoxins, plague.

Properties of bacterial exotoxin

1. Exotoxins are mainly produced by the Gram-positive bacteria but few Gram-Negative bacteria also involve.
2. Exotoxins are secreted extracellularly.
3. Chemically exotoxins are composed of polypeptides.
4.  Exotoxins denature above the  60 degrees centigrade temperature and by ultraviolet light.
5. Exotoxins are one of the most potent toxins. Some exotoxins are hundred to 1 million times as strong as strychnine.
6. Exotoxin is highly specific some of them act as a neurotoxin or cardiac muscle toxin.
7. The exotoxin has strong antigenicity which can stimulate antibody production and immunity.

Structure of bacterial exotoxin

• Most of the exotoxin has two structural domain such as A Subunit and B Subunit.
• A subunit or active domain who is responsible for the toxicity.
• B subunit or binding domain which binds the A domain to a specific cellular receptors and transfers A subunit into the cell.
• A and B both subunits are together joined by disulfide Bond.

Types of bacterial exotoxins

Based on biological activities exotoxin are three types ;

1. Enterotoxin: Enterotoxin only affects the gastrointestinal tract. Example, Cholera toxin.
2. Neurotoxin:   Neurotoxin only affects the nervous systems.  Example, Botulinum toxin.
3. Cytotoxin:  Cytotoxins affect the cells in a variety of tissues. Example Diphtheria toxin.

Also Read: ELISA test: Procedure, Principle, Types, and Application.

Bacterial Endotoxin

Endotoxins are the lipopolysaccharide which present in the outer membrane of Gram-Negative bacteria. Endotoxin is released when the microorganism lyses, or sometimes releases during cell division. The lipid A protein of the LPS is responsible for the toxicity of endotoxin.

Example: Salmonellosis, tularemia, endotoxic shock.

Properties of bacterial endotoxin

• Endotoxins are mainly produced by the Gram-Negative bacteria.
• Endotoxins are bonded within the bacterial cell wall and released upon the death of the bacterium.
• Endotoxin is mainly composed of lipopolysaccharide complexes.
• Endotoxins are relatively stable and can withstand several hours above 60-degree centigrade.
• The toxicity of endotoxin is weak but can be fatal in relatively large doses.
• The effect of endotoxin is non-specific.
• The endotoxin can cause a high fever or high temperature.

Source of Bacterial Toxin

There are present different types of bacterial toxin, some of them are most toxin, which can caus death. Each of these Bacterial toxins are descibed in below;

Botulinum toxin

Botulinum toxin also known as a Botox. It is a type of Neurotoxic protein, which mainly produced by Clostridium botulinum. Botulinum toxin commercially used in medical and cosmetic purposes. Botulinum toxin is the most poisonous substance known. Botulinum toxin can enter into the host body through a wound or intestinal infection or by ingesting preformed toxin in food. 

Botulinum toxin act by preventing the release of neurotransmitter acetylcholine From the ending point of exons (neuromuscular junction). As a result, it causes flaccid paralysis. The diseases caused by this type of Bacteria are known as botulism.

Role in Disease

Clostridium botulinum  produces a Neurotoxin which is responsible for a life threatening disease called botulism. Botulism disease only spread through the unprotected foods or contaminated foods with  clostridium botulinum.

Botulism disease has few symptoms such as constipation, poor feeding, bad temper, excessive drooling when feeding, sagging eyelids, flat facial expression, lethargy and listlessness, respiratory difficulties, slow or improper reflexes, weak crying weakly, etc.

Prevention of Botulism

1. Don’t feed  honey or corn syrup to infants under 12 months of age
2. Before eating ensure that all foods are well-cooked.
3. Avoid eating uncovered foods.
4. Avoid Canning food.
5. Before cooking, wash vegetables.
6. Store foods in a safe temperature.

Types of Botulinum Toxin

There are present seven types of botulinum toxin such as;

1. Botulinum A
2. Botulinum B
3. Botulinum C
4. Botulinum D
5. Botulinum E
6. Botulinum F
7. Botulinum G

Application of Botulinum Toxin

1. Mostly type A and type B botulinum toxin is capable to cause disease in the human body and they also used commercially in medical purposes (medicine ).
2. Type E and F can cause disease and the human body and remaining other botulinum toxin causes disease in other animals.
3. Use for the treatment of muscle spasticity.
4. Use for the treatment of excessive sweating.
5. Botulinum toxin also used in Cosmetics.

Side effect of Botulinum Toxin

1. If this toxine injected in wrong muscle then it can cause temporary paralysis of unintended muscles.
2. The cosmetic side effect (If someone using a Cosmetic which has botulinum toxin)of these botulism toxins is partial facial paralysis, muscle weakness, and trouble swallowing. The cosmetic Side Effects can be more serious.
3. The side effect of therapeutic use is arrhythmia, heart attack, and in some cases seizures, respiratory arrest, and death.

Staphylococcus Aureus

Toxin of staphylococcus aureus is responsible for Staph food poisoning, which is a type of gastrointestinal illness. About more than 25% of people and animals have staphylococcus aureus on their skin but they have the ability to produce exotoxin which causes food poisoning.

Role of Staphylococcus Aureus in Infection

1. Staphylococcus toxin can cause skin infection, such as boils, folliculitis, impetigo, cellulitis, and more severe, invasive soft-tissue infections.
2. Staphylococcus toxin is also responsible for food poisoning.
3. Staphylococcus in toxin also causes bone and joint infection.
4. Staphylococcus sometimes causes bloodstream infection,  if somehow staphylococcus enters into our bloodstream then it can infect other vital organs and can cause  infective endocarditis, septic arthritis, and osteomyelitis.

Prevention

1. To prevent skin infection, always stay clean and wash your body surface with soap, hot water.
2. To prevent food poisoning, frequently wash your hands with soap and water before cooking or serving food. Store foods below 5 or above 60 degree centigrade.
3. To prevent bloodstream infection,  always keep your wound clean, and covered. Use Antibiotic to prevent the bloodstream infection.

Types of Staphylococcus Toxin

Staphylococcus toxin is divided into three classes, Each of these stocks is related to a specific disease.

1. Superantigens:  this type of antigen is responsible for toxic shock syndrome.
2. Exfoliative toxins:  Exfoliative toxins are responsible for Exstaphylococcal scalded skin syndrome in infants and young children.
3. Other toxins: There are present other staphylococcus toxins, which act only on the cell membrane,  such as alpha-toxin, beta toxin, delta toxin, and several bicomponent toxins.

Bordetella pertussis or Pertussis toxin

Bordetella pertussis produces a protein-based AB5-type exotoxin which is known as Pertussis toxin (PT). This type of toxin act by inhibiting the early requirement of neutrophils and macrophages, and then interferes with the early synthesis of chemokine and the inhibition of the neutrophil chemotaxis. Researchers say that this type of toxin can be used for the treatment of a number of common human ailments, including hypertension, viral infection, and autoimmunity.

Role of Bordetella pertussis in Infection

This toxin is responsible for whooping cough. Pertussis toxin colonies in our respiratory tract and cause infection.

First, Pertussis attach to the cilia of the respiratory epithelial cells then irt started to synthesis toxins that paralyze the cilia. After that it causes inflammation of the respiratory tract, which affects the clearing of pulmonary secretions.

Prevention

1. The best way to prevent this infection is vaccination.  CDC recommended vaccines for Infants, Children, Adolescents, and Adults. 
2. Use Antimicrobial agents such as Azithromycin, Clarithromycin, Erythromycin.

Anthrax toxin or Bacillus anthracis

Anthrax toxin is produced by the viral strain of bacillus Anthrax. It is a type of exotoxin which is composed of three important proteins. The three proteins include a cell-binding protein, known as a protective antigen (PA), and two enzyme components, called edema factor (EF), and lethal factor (LF). 

Role of Anthrax toxin in Infection

Anthrax toxin is responsible for the disease Anthrax. There are present different types of Anthrax  infection. The type of  Anthrax infection depends on How Anthrax enters the body.  Anthrax can enter in our body through skin, lungs, or gastrointestinal system. If the Anthrax disease is not treated then it will spread throughout the body and will cause death.

There are present four type of Anthrax infection such as;

1. Cutaneous:  this is a most common type of Anthrax infection which developed within 1 to 7 days after infection 
2. Inhalation:  this infection is considered as the most deadly form of Anthrax. The infection develops within one week after infection. 
3. Gastrointestinal:  This type of Anthrax infection developed within 1 to 7 days after infection.
4. Injection: This is the most rare form of Anthrax infection. 

Prevention

1. There are two recommended antibiotics which can prevent the spread of Anthrax infection such as Ciprofloxacin and doxycycline.
2. Anthrax Vaccine Adsorbed (AVA) Can be used for the prevention of Anthrax infection. This vaccine is approved by the Food and Drug Administration (FDA).

Reference

• Wilkipedia, “Exotoxin“
• textbookofbacteriology,”Bacterial Protein Toxins“
• sciencedirect, “Microbial Toxins“