Lipopolysaccharides? E.coli O157:H7? What’s the “O” in E. coli O157:H7 called “O157”
According to the National Institute of Health, many foodborne diseases are caused by Gram-negative bacteria, like Escherichia coli (NIH). But what is the toxic component of bacteria makes humans suffer from septic shock and fever, often associated with food poisoning or infection?
The largest component of the outer-membranes of Gram-negative bacteria are composed
of chains of lipopolysaccharides. Conceptually, imagine a shaggy rug. At the base of the rug is a coarse mesh of the strands, the sturdy cell wall. Hooked and extending off the mesh are the shaggy strands of chunky yarn; on the bacterial cell well, these are the lipopolysaccharides. If the bacterial cell wall is not already encapsulated in an endospore or biofilm, the lipopolysaccharides will be exposed on the cell surface, like a shaggy rug.
The lipopolysaccharides are a three-part system including the following:
1.) Lipid A, the base of the stand and endotoxin
2.) The core sugar chain
3.) Lastly, the O antigen the end of the strand
Lipid A is the lipid that anchors the lipopolysaccharide to the bacteria’s cell wall, and these lipids are responsible for most of the toxicity. This anchoring lipid, Lipid A, fragments off when your immune system attacks the Gram-negative bacteria. During this bacterial lysis (splitting), of this endotoxin, the fragments cause your body to experience septic shock or fever.
The core sugar chain is the sugar component or saccharide component of lipopolysaccharides.
The O antigen is the unique characteristic of the chain. The special arrangement of the molecules gives scientists the opportunity to identify different strands of bacteria from one another. For example, E. coli O157:H7 is called “O157” because this strand of E. coli has the 157th type of O antigen strand.
In summary, when your immune system attacks a Gram-negative pathogen in your body, the endotoxin that fragments off of the bacterial membranes causes toxic shock and fever.
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