Environ Sci Technol. 2012 Dec 18;46(24):13448-54. doi: 10.1021/es302760s. Epub 2012 Dec 6.
A Survey of Drug Resistance bla Genes Originating from Synthetic Plasmid Vectors in Six Chinese Rivers.
Source
College of Life Sciences, Sichuan University , Chengdu, Sichuan Province 610064, People's Republic of China.Abstract
Antibiotic resistance poses a significant challenge to human health and its rate continues to rise globally. While antibiotic-selectable synthetic plasmid vectors have proved invaluable tools of genetic engineering, this class of artificial recombinant DNA sequences with high expression of antibiotic resistance genes presents an unknown risk beyond the laboratory setting. Contamination of environmental microbes with synthetic plasmid vector-sourced antibiotic resistance genes may represent a yet unrecognized source of antibiotic resistance. In this study, PCR and real-time quantitative PCR were used to investigate the synthetic plasmid vector-originated ampicillin resistance gene, β-lactam antibiotic (blá), in microbes from six Chinese rivers with significant human interactions. Various levels of blá were detected in all six rivers, with the highest levels in the Pearl and Haihe rivers. To validate the blá pollution, environmental plasmids in the river samples were captured by the E. coli transformants from the community plasmid metagenome. The resultant plasmid library of 205 ampicillin-resistant E. coli (transformants) showed a blá-positive rate of 27.3% by PCR. Sequencing results confirmed the synthetic plasmid vector sources. In addition, results of the Kirby-Bauer disc-diffusion test reinforced the ampicillin-resistant functions of the environmental plasmids. The resistance spectrum of transformants from the Pearl and Haihe rivers, in particular, had expanded to the third- and fourth-generation of cephalosporin drugs, while that of other transformants mainly involved first- and second-generation cephalosporins. This study not only reveals environmental contamination of synthetic plasmid vector-sourced blá drug resistance genes in Chinese rivers, but also suggests that synthetic plasmid vectors may represent a source of antibiotic resistance in humans.- PMID:
- 23215020
- [PubMed - in process]
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Comment from UC Berkeley microbiologist Dr. Ignacio Chapela:
Paper demonstrating the escape and establishment of transgenic DNA from GMOs in
all rivers tested in China. Salient points:
1. A novel method was used to select and isolate those bacteria from the river
water which contained DNA suspected to derive from GMOs. These were then
carefully studied to demonstrate that the DNA could not have come from other
sources (e.g. mutation/natural selection).
2. Although the numbers varied, and absolute amounts of the transformed bacteria
could not be measured, every river sampled was shown to contain these organisms.
3. The exact origin of the transgenic DNA incorporated into native bacterial
populations was not determined. It could come from intentional releases (such as
agricultural fields) or from unintentional escapes from contained situations
(labs, industrial facilities).
4. These bacteria all have in common the fact that they acquired antibiotic
resistance markers from transgenic origin (the markers were used to select the
bacteria in the first place). Antibiotic resistance in free-living bacteria is
not a good thing for those who may one day want to use antibiotics to fend-off
infections (e.g. patients in hospitals).
5. Nevertheless, the antibiotic resistance is not at all the most important
point of this paper (even when the authors themselves seem to think it is).
Looking for antibiotic resistance was the easiest feasible way to do this work
and it also has the obvious medical implications, but this is only a fraction of
the many other sequences of transgenic DNA which must be expected out there in
the environment, from all kinds of origins, with all kinds of possible
functions. This paper is the equivalent of the proverbial sighting of the
iceberg's tip. A polaroid photo of a small part of what must be a very large and
relevant phenomenon.
6. The question which beggars belief is: why is it that nobody in the "West" has
been able to follow up on such leads, or even suggest doing this kind of work?
One thinks of the work begun at NYU on soils, which attracted so much negative
campaigning, and nary a recognition.
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