Bacteria That Produce Dangerous Toxins

FROM THE LECTURE SERIES: An Introduction to Infectious Diseases

By Barry C. Fox, M.D., University of Wisconsin

The human body contains innumerable pathogens that release harmful toxins, which can be quite fatal to humans. And, several vaccines have been developed to fight against the pathogens or germs in the human body. The DTP vaccine one such class of combination vaccines for three infectious diseases in humans—diphtheria, tetanus, and bordetella pertussis.

Image of DTP vaccine.
Due to the DTP vaccine, deaths from pertussis have greatly declined. (Image: Jarun Ontakrai/Shutterstock)

When a person coughs or sneezes, the germs are spread through tiny droplets into the air, where they can infect others within an 8-foot range. This allows the bacteria to enhance its own survival. They also can spread from the mucus on a used tissue or from silverware that has been in an infected person’s mouth.

What Causes Diphtheria?

Corynebacterium diphtheria has a Gram-positive staining, is aerobic, and has a rod-like shape. Before the DPT vaccine was developed, this germ sometimes found its way to the back of a person’s throat and into the nose. It caused a sore throat, fever, and swollen glands, but the classic sign of diphtheria disease is a thick sheet of grey material that covers the back of the throat, blocking the airway and causing difficulty breathing.

Diphtheria infections are somewhat unusual since the bacteria could only invade the surface cells of the throat. However, the protein toxin produced spreads through the circulation and non-specifically attacks other cells of the body.

Severe infection with diphtheria toxin can cause death by interrupting the function of essential organs, like the heart, kidneys, liver, and lungs, blocking all protein synthesis in affected cells by interfering with a key enzyme at the ribosomal site.

In the U.S., due to the efficacy of the DPT vaccine, cases of diphtheria are extremely rare. However, Russia and Eastern Europe are not as fortunate and have thousands of cases due to low rates of vaccination.

Learn more about emerging and reemerging diseases.

Bordetella Pertussis

Bordetella pertussis is extremely contagious, with germs traveling through respiratory droplets that cause the illness, whooping cough. After the germ settles in the respiratory tract, the bacterium uses several toxins to bind and destroy the epithelial or surface lining cells.

The pertussis toxin enters cells and interferes with communication between the cells. It also releases a throat cytotoxin, which causes the destruction of hairs, known as cilia, on the epithelial cell layer. Cilia are responsible for keeping our airways free from bad bacteria.

A hallmark of pertussis is its violent coughing fits that are so frequent and forceful that make it hard to breathe. After coughing, individuals infected with pertussis need to subsequently take an inhalational breath that results in a whooping sound.

These coughing fits can last more than ten weeks, or more, even if the germs have been killed by antibiotics, due to the damage inflicted on the epithelial cells. Severe cases of this disease affect mostly infants and young children, particularly toddlers under the age of one. These babies sometimes contract pneumonia and end up in intensive care.

Due to the DTP vaccine, deaths from pertussis have greatly declined, but illness is occasionally still seen in infants who have not been fully immunized and in unvaccinated adults.

Virulence Factors of Gram-Negative Bacteria

Image of Gram-negative bacteria.
Gram-negative bacteria are pathogenic organisms whose outer membrane is typically hidden by a viscous capsule or layer that camouflages cell antigens. (Image: Kateryna Kon/Shutterstock)

The infamous plague bacteria, Yersinia pestis, is a perfect example of a deadly virulence factor of Gram-negative bacteria, known as endotoxin.

With plague, the outer Gram-negative cellular membrane also contains a special compound known as lipopolysaccharide or LPS. The LPS has a structural chain that extends into the surrounding environment. On the inside of the LPS is a special compound known as Lipid A. Lipid A is extremely toxic to humans and forms the basis of endotoxin. When bacterial cells are broken apart by the immune system or by antibiotics, fragments of the cell membrane containing Lipid A are released into the bloodstream. This can trigger a deadly cascade of events known as the sepsis syndrome, or more commonly known as blood poisoning.

This is a transcript from the video series An Introduction to Infectious Diseases. Watch it now on The Great Courses Plus.

Toxic Bacteria Vs. the Immune System

Another factor that helps bacteria escape the immune system are thick capsules, which are protective barriers made of sugars outside the cell membranes. These enable bacteria to be more evasive because the white blood cells, which are part of our immune system, are subsequently unable to swallow the germs.

The germ Streptococcus pneumoniae, which is the most common cause of bacterial pneumonia, has a very thick and elusive capsule and is one of the reasons that the pneumococcal vaccine is so important to prevent pneumonia.

A virulent factor of Gram-negative bacteria is a biofilm that is an extracellular sugar network that forms a scaffolding around the bacteria. The biofilm, basically a slime layer, allows bacteria to bind to artificial devices such as plastic intravenous catheters or even artificial joints. The germs go into hibernation, and the biofilm protects the germs from the immune system, like using a large umbrella in the rain.

Some bacteria may be swallowed by our white blood cells but manage to survive inside of these cells unharmed. These bacteria inhibit specific killing mechanisms and are thus safe from our immune systems.

Mycobacteria, including Mycobacterium tuberculosis, or TB, possess a unique cell membrane, which contains mycolic acid, and can survive intracellularly. This is one of the reasons that TB poses one of the three largest threats to world health.

Learn more about our immune system.

Clostridium Tetani

Clostridium tetani is a bacterium that can generally be found in the soil everywhere. It causes tetanus, an illness that leads to spasms of all the muscles of the body. One hallmark of the disease is the jaw of the mouth getting stuck, giving it the nickname “lockjaw”.

Tetanus toxin, produced locally by the bacteria, spreads throughout tissue spaces into the blood. It enters the nervous system and attacks the site where nerves meet muscles. The tetanus toxin causes spastic paralysis by blocking the release of a chemical responsible for the transmission of a nerve impulse—γ-aminobutyric acid, or GABA.

GABA works by slowing down muscle fibre contraction. The net effect is that the muscles are over-performing, leading to the spasm that is visually seen.

Another early symptom in the face and jaw includes stiffness of the neck and trouble swallowing. The toxin can penetrate larger nerve bundles, and even into the brain. Death can result from heart rhythm disturbances or respiratory paralysis.

Tetanus Vaccine

Image of tetanus vaccine.
Tetanus vaccination of infants boost their immunity system and saves several lives every year. (Image: OneSideProFoto/Shutterstock)

Immunization and the tetanus vaccine utilize a modified protein toxin form, known as a toxoid.

Due to the early vaccinations, there are less than 30 cases of tetanus in the United States every year. These cases tend to occur in unvaccinated children. Parents should be advised of the seriousness of tetanus and be informed that there are no other preventive measures other than vaccination to protect their children from tetanus.

Common Questions about Toxic Bacteria

Q: What is the DTP vaccine?

The DTP vaccine is a class of combination vaccines for three infectious diseases in humans—diphtheria (D), tetanus (T), and pertussis (pertussis) (P).

Q: What is Bordetella pertussis?

Bordetella pertussis is a Gram-negative bacterium that is extremely contagious through respiratory droplets that causes the illness whooping cough.

Q: What does Clostridium tetani cause?

Clostridium tetani cause tetanus, an illness that leads to spasms of all the muscles of the body.

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