Re: Genetically modified foods and intestinal bacteria


dkomo wrote:
> I ran across two references to studies which show that when humans
> digest genetically modified foods, the artificially created genes
> transfer into and alter the character of the beneficial bacteria in
> the intestine. This could get interesting. I don't have time to
> chase down the journals to find the references. Does anyone know
> anything about this?
>
> Heritage, J. (2004). "The fate of transgenes in the human gut." Nature
> Biotechnology 22(2): 170+.
>
> Netherwood, T., S. M. Martin-Orue, et al. (2004) "Assessing the
> survival of transgenic plant DNA in the human gastrointestinal tract."
> Nature Biotechnology 22(2): 204+

the first ref is a "News and Views" bit on the second study. In that
paper they found that unlike animal models, fragments of the transgene
epsps remained in the waste. This is not really very surprizing as
there are undoubtably many differences between human and non human
digestive processes (the other models were in chickens and hogs). They
did find, however, that it is completely degraded in the colon (see
note below).

The interesting finding is that although they could find no evidence of
gene transfer from the plant material eaten by the subjects to their
gut flora, there was evidence that some of the patients already possess
fragments of the transgenes in their gut flora. This indicated past
consumption of the GM crops.

>>From the discussion of that paper;

"Gene transfer from GM soya to the intestinal microflora appears to
have occurred before the feeding experiment in three of the
ileostomists, as a single meal containing very high levels of GM soya
did not enhance plant to bacterial gene transfer; the levels of
transgene in the microbes (measured in subculture 6) derived from the
digesta of the T 0 min (before GM meal ingestion) and T 360 min (after
consumption of the GM meal) samples from Subjects 1, 4 and 6 were
similar (T 0 min results in Table 2; T 360 min data not shown). This
gene flow is therefore likely to reflect long term consumption of GM
foods. The transgene-derived PCR product was evident only when the
microbes in the T 0 digesta had been expanded by culturing, indicating
that the epsps-containing bacteria was a very small component of the
small intestinal microflora. It should be noted that these bacteria
contained only a fragment of epsps; the full-length gene was not
detected in these microbes. The observation that the bacteria
containing the GM soya transgene could not be identified from >2 106
colonies screened on agar plates again indicates that the microbes
containing the transgene represent a very minor component of the small
intestinal microflora."

Also;

"In conclusion, we have shown that a small proportion of the transgenes
in GM soya, like the native soya DNA, survives passage through the
human upper gastrointestinal tract but is completely degraded in the
large intestine. Although we found some evidence of preexisting gene
transfer between the GM soya and the human small intestinal microflora,
the bacteria containing the transgene represented a very small
proportion of the microbial population, and there was no indication
that the complete transgene had been transferred to the prokaryotes.
Thus, it is highly unlikely that the gene transfer events seen in this
study would alter gastrointestinal function or pose a risk to human
health. Nevertheless, the observed survival of transgenic DNA from a GM
plant during passage through the small intestine should be considered
in future safety assessments of GM foods."

Note; ileostomists are people who've had a proteion of their small
intestine resected and the contents diverted to a coleostomy bag.
Several reports have shown that irrespective of the fact that for most
ileostomists, there is little or no colon tissue remaining in the
digestive path, they still are good models for human digestion.

>
>
> --dkomo@xxxxxxxx

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