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Concept
Hemolysin
Summary
Hemolysins or haemolysins are lipids and proteins that cause lysis of red blood cells by disrupting the cell membrane. Although the lytic activity of some microbe-derived hemolysins on red blood cells may be of great importance for nutrient acquisition, many hemolysins produced by pathogens do not cause significant destruction of red blood cells during infection. However, hemolysins are often capable of lysing red blood cells in vitro.
While most hemolysins are protein compounds, some are lipid biosurfactants.
Many bacteria produce hemolysins that can be detected in the laboratory. It is now believed that many clinically relevant fungi also produce hemolysins. Hemolysins can be identified by their ability to lyse red blood cells in vitro.
Not only are the erythrocytes affected by hemolysins, but there are also some effects among other blood cells, such as leucocytes (white blood cells). Escherichia coli hemolysin is potentially cytotoxic to monocytes, lymphocytes and macrophages, leading them to autolysis and death.
Visualization of hemolysis (UK: haemolysis) of red blood cells in agar plates facilitates the categorization of Streptococcus.
One way hemolysin lyses erythrocytes is by forming pores in phospholipid bilayers. Other hemolysins lyse erythrocytes by hydrolyzing the phospholipids in the bilayer.
Many hemolysins are pore-forming toxins (PFT), which are able to cause the lysis of erythrocytes, leukocytes, and platelets by producing pores on the cytoplasmic membrane.
Hemolysin is normally secreted by the bacteria in a water-soluble way.
These monomers diffuse to the target cells and are attached to them by specific receivers. After this is done, they oligomerize, creating ring-shaped heptamer complexes.
Hemolysins can be secreted by many different kinds of bacteria such as Staphylococcus aureus, Escherichia coli or Vibrio parahemolyticus among other pathogens.
We can take a look at the bacterium Staphylococcus aureus as a specific example of pore-forming hemolysin production.
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Microbial toxin
Microbial toxins are toxins produced by micro-organisms, including bacteria, fungi, protozoa, dinoflagellates, and viruses. Many microbial toxins promote infection and disease by directly damaging host tissues and by disabling the immune system. Endotoxins most commonly refer to the lipopolysaccharide (LPS) or lipooligosaccharide (LOS) that are in the outer plasma membrane of Gram-negative bacteria. The botulinum toxin, which is primarily produced by Clostridium botulinum and less frequently by other Clostridium species, is the most toxic substance known in the world.