More Info on London Streptococcus ?

Kevin Sanderson sanderso at tasman.cc.utas.edu.au
Wed Jun 1 21:34:19 EST 1994


R.Burge at bay.cc.kcl.ac.uk (Richard Burge) writes:

>In article <CqD5EE.2K8 at usenet.ucs.indiana.edu> jgraham at bronze.ucs.indiana.edu 
>(the End) writes:

>It's a beta-haemolytic group A streptococcus. There are no indications that 
>this strain is any more antibiotic resistant than normal (it is still 
>subsceptible to penicillin if caught early enough), but it is a hell of a lot 
>more virulent - it appears to be producing tissue necrosing toxins in much 
>higher levels than would normally be expected. 

>So, could someone who knows more about microbiology than me (not difficult!) 
>care to expand on the above?

Well I'm not sure I know more microbiology but here goes,
the group A streptococci produce numerous extracellular products that are
involved in the infection process. These include

Haemolysins - destroy red blood cells
Spreading factors - primarily digest (dissolve) connective tissue (the stuff
that holds muscle/skin together) and fibrin (dissolves blood clots).

So even "normal" bugs are well set up as "flesh-eaters" although in most
instances infections are mild. Production of greater amounts or enhanced/
new spreading factors could account for the symptoms described in the papers.

>How can a bacterium suddenly become so much more virulent? I saw something 
>about a bacteriophage being involved somewhere. Are flesh-eating toxins the 
>sort of thing coded for in virii?

Well viruses conferring flesh eating abilities sounds a lot like the plot
for a cheap movie ;) but bacteriophage (viruses that infect bacteria) can
encode toxins or other things, so that infected bacteria do produce toxin and
non-infected bacteria do not. 
 
>Also, to quote The Independent, "scientists believe that the bacterium is able 
>to evade the bodies natural defences by virtue of a slime coating" (or words 
>to that effect) - what the hell are they talking about here? Some 
>immunoglobulin-binding cell-surface glycolipid or something?

Group A streptococci can produce a surface layer of carbohydrate, known as
a slime coating or capsule. It's a bit like them being embedded in jelly.
The capsule is composed of hyaluronic acid, a glycosaminoglycan that is
present and has the same chemical structure in all animals. This means
it is non-antigenic. So the streps can sit inside their jelly house protected
from antibodies pumping out toxins. Which is quite a neat system.

Hope this helps.
Kev

PS There are some fairly sweeping generalisations in what I said. Any decent
medical microbiology textbook will have a section on streptococci for
background info. The tabloid press (unfortunately) seems to be the only
place to get "information" on the mutant/killer/world devouring strain.
--
Kevin Sanderson
Department of Pathology           email: Kevin.Sanderson at path.utas.edu.au
University of Tasmania            phone: 61-002- 35 4825



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