Laboratory K-12 colonizing our guts?

Trond Erik Vee Aune via (by trondaun from
Wed Jun 20 01:19:37 EST 2007

Thank you very much,

This was perfect, exactly what I sought.

Trond Erik

David F. Spencer wrote:
> Trond Erik Vee Aune wrote:
>> Dear all,
>> Yesterday we started discussing the possibility of our recombinant 
>> E.coli K-12 establishing themselves in our guts. I know there were 
>> some controversy around this in the 70's, but I haven't been able to 
>> find out what the conclusions were. Here are some specific questions:
>> * Can our modern laboratory K-12 acutally establish themselves in our 
>> guts, competing with our natural flora?
>> * What if after an antibiotics cure when the natural flora is greatly 
>> reduced?
>> * Can expression of recombinant proteins from such bacteria cause 
>> problems with human health)
>> I would especially like any references to articles that handle these 
>> questions.
>> Best regards,
>> Trond Erik
> E.coli K-12 was the first of the primary E. coli isolates (1922, from 
> the stool of a diptheria patient).
> Here is a section from a good summary of E. coli, including K-12, taken 
> from:
>  In order to evaluate K-12's potential to colonize the human intestine 
> the following should be addressed: (1) the characteristics relevant to 
> E. coli colonization of the human colon, and how K-12 compares to other 
> E. coli in terms of these traits, and (2) data relevant to colonization 
> potential of K-12 strains.
>  The binding of an E. coli to the mucosal surface of the colon requires 
> two factors. The first factor is the production of a specific glycocalyx 
> or fimbriae from the surface of the bacterium. This specific glycocalyx 
> recognizes a specific lectin on the surface of the enterocyte lining of 
> the human colon. The glycocalyxes appear to bind to structures such as 
> the mucus glycoproteins elaborated from the goblet cells of the 
> intestine. In Gram-negative bacteria, the polysaccharide chains arising 
> from the core of the lipopolysaccharides in the outer membrane appear to 
> be the major ones which affect binding to the colon.
> E. coli K-12 is defective in at least three cell wall characteristics. 
> The outer membrane has a defective lipopolysaccharide core which affects 
> the attachment of the O-antigen polysaccharide side chains (Curtiss, 
> 1978). Second, it does not have the type of glycocalyx required for 
> attachment to the mucosal surface of the human colon (Edberg, 1991) as a 
> result of the altered O-antigen properties noted above. Finally, K-12 
> strains do not appear to express capsular (K) antigens, which are 
> heat-labile polysaccharides important for colonization and virulence 
> (Curtiss, 1978).
>  K-12, thus, is not able to colonize the human intestinal tract under 
> normal conditions, even after ingestion of billions of organisms 
> (Anderson, 1975, Cohen et al., 1979., Levy and Marshall, 1981; Levy et. 
> al, 1980, Smith, 1975). As noted above, K-12 is defective in cell wall 
> components relevant to the ability to recognize and adhere to the 
> mucosal surface of colonic cells (Curtiss, 1978). The normal flora in 
> residence in the colon thus can easily exclude K-12, and prevent it from 
> colonizing the human colon.
> There was a lot of fuss in the 70's about the safety of plasmid 
> transformed E. coli which resulted in the production of the cell 
> chi_1776, an extremely enfeebled strain that was essentially impossible 
> to actually work with.

Trond Erik Vee Aune
Department of Biotechnology, NTNU

- Must be sad being a dyslectic, agnostic insomniac, lying
   awake during the night, wondering if there really is a dog

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