Endotoxins and Exotoxins

Bacterial toxins are substances capable of causing damage to the body.

They can be classified as exotoxins and endotoxins. Toxins are defined as soluble substances, generally of protein origin, which alter the normal metabolism of the host cell or tissue with the same effects.

Endotoxins have diverse and complex biological activities. They can bind to various body cells, particularly the specific serum proteins, LBP, causing a response from the organism, resulting in septicemia in humans. The process is present in the LPS outer membrane of the cell wall and is released only after the destruction of the bacteria.

When Gram-negative bacteria cause the infection, the disruption of the bacterial cell and the release of endotoxin occurs, which causes a response of the human immune system in general, such as fever, weakness, pain, shock, and vasodilation. . In large quantities, the toxin can lead to septicemia, and consequently death.

The primary diseases caused by endotoxins are typhoid fever, urinary tract infections, and meningococcal meningitis. When Gram-positive bacteria cause the condition, the toxin released by the bacterial cell wall is similar to the effect caused by the endotoxin.

The exotoxins are divided into three groups according to their interactions with the host cells. These affect mainly cellular functions, nerve cells, and the gastrointestinal tract.

We find superantigens and ST toxins in the first group, which act only on the cell surface. Among the bacteria that produce superantigens, the most recent study found Staphylococcus aureus and Streptococcus pyogenes. ST toxins (heat-stable toxins) are produced mainly by the bacterium Escherichia coli, attacking intestinal epithelial cells, particularly causing diarrhea.


The toxins damage the cytoplasmic membrane in the second group, causing cell death. Bacteria use these toxins to kill phagocytes and break down the phagosome membrane. They also lyse erythrocytes for the iron of hemoglobin. These toxins form pores in the cell membrane.

The third group has the highest number of toxins and the most important virulence factors. The following toxins are found in this group: diphtheria toxin, cholera toxin, LT, Shiga toxin, botulinum toxin, tetanus toxin, pertussis toxin (whooping cough), invasive guanylate cyclase (whooping cough), and Exotoxin A (pulmonary infections in patients with cystic fibrosis).

There is also a significant group of proteins injected directly into the cytosol of host cells, causing various effects. Hydrolytic enzymes such as hyaluronidase, collagenase, and protease are produced by many bacteria that can degrade components of the extracellular matrix, which alters the structure of the tissue and achieves the generation of several nutrients that are used by bacteria.