5.5—GM foods are irrelevant to the rise of antibiotic resistant bacteria

Genetically modified foods pose a negligible risk of increasing infectious diseases caused by antibiotic resistant bacteria.

See Genetic Roulette’s False Claims at Bottom of Page

Analysis of Peer-Reviewed Research:

Some transgenic crops contain antibiotic resistance genes as selection markers that were used during the process of transgene construction. The proliferation in gut bacteria of these markers would require first the uptake of the functional resistance gene by a gut bacterium, and then a selective advantage for that bacterium to survive and multiply. The improbability of the gene transfer has already been mentioned in earlier sections. The consequences of the very improbable transfer should be judged against the background of antibiotic resistance already present in intestinal bacteria. Our gut already contains billions of bacteria carrying resistances to kanamycin and ampicillin, the two most commonly used antibiotic marker genes in GM crops. There is a huge reservoir of ampicillin resistance genes in soil and these can be readily transmitted to gut bacteria.  Current medical opinion is that the antibiotic markers used in commercialised crops do not pose any infectious disease risk.

Jeffrey Smith’s treatment this topic is an unfortunate attempt to confuse the public about the top priority for countering antibiotic resistant bacteria (Saylers 1996, Salyers, Whitt 2005) — which is to avoid overusing and misusing antibiotics.

1. GM foods will not change antibiotic resistance in bacteria. Expert scientific opinion has repeatedly reaffirmed that the presence of antibiotic resistance genes in GM foods is unable to change the level of antibiotic resistance present in gut bacteria (Bennett PM and others 2004, EFSA 2004, Salyers A (n.d.), van den Eede and others 2004).

2. Genetic Roulette avoids explaining why regulatory authorities have approved the markers currently used in crops. Smith avoids mentioning expert advice and evidence that contradicts his assertions about antibiotic resistance, and does not provide access to the detailed and extensive deliberations that led to approvals of crops having antibiotic markers (Bennett and others 2004. EFSA 2004,  Goldstein and others 2005,  Miki , McHugh 2004, Ramessar and others 2007, Salyers (n.d.), van den Eede and others 2004).

3. Antibiotic resistant bacteria are numerous in the gut whether or not there is any antibiotic marker in GM food. The antibiotic resistance genes present in genetically modified foods are already easily found in any human intestine in a form that frequently moves around between different bacteria and can easily take up residence in new bacteria. Bacteria will frequently contain small chromosomes called plasmids that commonly carry genes for antibiotic resistance. These plasmids can replicate by injecting copies of themselves into other bacteria without exposing their DNA to digestive juices. Once injected into a new bacteria that they can replicate independently. Plasmids are widely known to be involved in the spread of antibiotic resistance in bacteria. Their spread is promoted by the use of antibiotics and it is massive overuse of antibiotics that is the main factor promoting the spread of diseases that cannot be treated by antibiotics (Bennett and others 2004, Saylers 1996,  Salyers, Whitt  2005).

4. Huge numbers of diverse antibiotic resistance genes are present in soil bacteria. Most antibiotic resistance probably comes from soil bacteria, and the genes they carry genes can readily be disseminated from one species of bacteria to another on plasmids. The presence of genes providing resistance to ampicillin and related antibiotics is a well-investigated example. These genes are frequently found in soil bacteria. Growing genetically modified corn containing the ampicillin marker gene has no influence on abundance of this gene in soil bacteria (Demanèche and others 2008).

Bennett PM and others, Working Party of the British Society for Antimicrobial Chemotherapy (2004). An assessment of the risks associated with the use of antibiotic resistance genes in genetically modified plants: report of the Working Party of the British Society for Antimicrobial Chemotherapy. J Antimicrob Chemother. 2004 Mar;53(3):418-31. Epub 2004 Jan 28.”…the argument that occasional transfer of these particular resistance genes from GM plants to bacteria would pose an unacceptable risk to human or animal health has little substance. We conclude that the risk of transfer of AR genes from GM plants to bacteria is remote, and that the hazard arising from any such gene transfer is, at worst, slight.”

References

Demanèche S and others (2008). Antibiotic-resistant soil bacteria in transgenic plant fields. Proc Natl Acad Sci U S A. 105(10):3957-62. “Our results indicate that soil bacteria are naturally resistant to a broad spectrum of beta-lactam antibiotics… These high resistance levels for a wide range of antibiotics are partly due to the polymorphism of bla genes, which occur frequently among soil bacteria. The blaTEM116 gene of the transgenic corn Bt176investigated here is among those frequently found, thus reducing any risk of introducing a new bacterial resistance trait from the transgenic material.”

EFSA (2004). Opinion of the Scientific Panel on Genetically Modified Organisms on the use of antibiotic resistance genes as marker genes in genetically modified plants, The EFSA Journal (2004) 48, 1-18 www.efsa.europa.eu/EFSA/efsa_locale-1178620753812_1178620772328.htm accessed Dec 30 2008

Goldstein DA and others (2005). Human safety and genetically modified plants: a review of antibiotic resistance markers and future transformation selection technologies. Journal of Applied Microbiology 99:7–23

Miki B, McHugh S (2004). Selectable marker genes in transgenic plants: applications, alternatives and biosafety. J Biotech 107:193–232

Ramessar K and others (2007). Biosafety and risk assessment framework for selectable marker genes in transgenic crop plants: a case of the science not supporting the politics. Transgenic Res. 2007 Jun;16(3):261-80. Epub 2007 Apr 14.”Our conclusion, supported by numerous studies, most of which are commissioned by some of the very parties that have taken a position against the use of antibiotic selectable marker gene systems, is that there is no scientific basis to argue against the use and presence of selectable marker genes as a class in transgenic plants.”

Saylers A (1996). The real threat from antibiotics. Nature 384:304. Warns against sending the wrong messages to the public.

Salyers A (n.d.) Genetically Engineered Foods: Safety Issues Associated with Antibiotic Resistance Genes. Abigail Salyers, Department of Microbiology, University of Illinois, Urbana, IL, USA .www.seeeach.com/doc/176262_ROAR

Salyers AA, Whitt DD (2005). Revenge of the Microbes: How Bacterial Resistance is Undermining the Antibiotic Miracle. ASM Press.

van den Eede G and others (2004). The relevance of gene transfer to the safety of food and feed derived from genetically modified (GM) plants. Food and Chemical Toxicology 42:1127–1156