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How the “flesh-eating” bacteria really works. September 29, 2006

Posted by Hegemony in Health, Science.
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We’ve all heard of the “flesh-eating” bacteria. It sounds scary doesn’t it? It is scary, but not in the way you’d expect. To put it simply, the bacteria don’t actually eat you… YOU eat you. That probably doesn’t make a whole lot of sense as I’ve just explained it… Necrotizing fasciitis (as it’s properly called) is most frequently caused by a bacteria known as Streptococcus pyogenes.

Even a relatively minor abrasion can lead to infection if the bacteria is present. All the action takes place in the Fascia, a layer of connective tissue and blood vessels covering the muscle. The bacteria multiplies like any other, but this is the twist. The strains of S. pyogenes capable of causing necrotizing fasciitis produce a super-antigen.

So what’s a super antigen? It’s a regular antigen but super😉 But really… your immune system recognizes foreign material as “antigens”. Each T-cell and B-cell recognize only one antigen.

This specific antigen can be a part of the bacteria itself or something they secrete. This interaction is usually specific to the T-cell and causes them to become activated. T-cells then direct the immune response through the release of cytokines. Cytokines then activate other immune cells and attract them to the infected area. On average, an antigen activates 1 in 30,000 T-cells.

A super-antigen is not specific to a particualr T-cell. Rather, it simply binds (very strongly) to most T-cell receptors. This activates them just as if they had encountered their specific antigen. This process activates 1 in 5 T-cells… waaaaaaay more than should be activated. With all these cells secreting cytokines things get … confused.

You have immune cells called macrophages. These cells are what actually cause the damage. These are normally activated by T-cells. They phagocytose (take in) pathogens and destroy them. They have the ability to use oxygen radicals to kill these pathogens. With all those T-cells releasing cytokines these macrophages become over stimulated. They begin over producing oxygen radicals and bathe your tissues in them. This causes massive cell death and necrosis.

The treatment for necrotizing fasciitis is straight forward: surgical debridement. ALL the infected tissue must be removed to stop the infection. This often means removal of limbs. If the infection is not on an extremity the options are somewhat limited. Due to the extensive thrombosis caused by the infection antibiotics cannot reach the site of infection very well. The wounds can be irrigated with antibiotic solutions… but this is often ineffective.

This is a truly terrifying disease. Your own defences are turned against you in a matter of hours. The tissues are not really “eaten” but rather destroyed. The very cells meant to protect you can cost you your life.

Comments»

1. Pearl Barkley - December 13, 2006

I tutor biology and you have explained this very well. I came to this site while searching for information that links prions which cause mad cow’s disease in cows and Creutzfeld Jacob disease in humans. Can you help me out?

2. Hegemony - December 13, 2006

You may have seen this but: https://hegemony.wordpress.com/2006/11/21/how-do-prions-work/

The high homology of PrP among mammals is strong evidence. Look into Pruisner’s Theory.

3. Novi - March 26, 2010

Wow! this was very helpfull and explained everything i needed to know! in simple terms🙂
Thanks

4. Alex - October 11, 2012

Thanks for the article. Interesting and straight to the point.


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