This letter to the journal Nature outlines the safety risk of antibiotic resistance due to horizontal gene transfer from GMOs and points out that this is not the only risk that needs to be urgently addressed by the authorities.

Ampicillin threat leads to wider transgene concern


We are concerned by the suggestion, in your Editorial "Don't rely on Uncle Sam" (Nature 434, 807; 2005), that the US Food and Drug Administration does not consider the presence of the ampicillin-resistance gene in Syngenta's unapproved variety of genetically modified Bt10 maize to represent a safety problem.

This is not the view of the UK government's scientific advisers (the DEFRA Antimicrobial Resistance Coordination Group), who state that some important veterinary pathogens remain susceptible to ampicillin (K. L. Goodyear et al. J. Antimicrob. Chemother. 54, 959; 2004). They state that there is

"extremely low or no detected resistance in certain bacterial species", so that "any occasional transfer of resistance genes to these organisms would be a very significant event". If, as a result of such horizontal gene transfer, it became necessary to use more modern antimicrobials to treat animal disease, they write, "then there could be significant consequences for the consumer through the food chain".

The risk of horizontal gene transfer from genetically modified organisms (GMOs) is not a theoretical one. One study found that, after Bt genes in plasmid form were incubated in the saliva in a sheep's mouth for a few minutes, they could still transform Escherichia coli bacteria so that they developed antibiotic resistance (P. S. Duggan et al. Br. J. Nutr. 89, 159−166; 2003).

In addition, it is worth noting that the ampicillin-resistance gene in Bt10 maize and other genetically modified crops is a remnant of the bacterial plasmid inserted into these varieties, and would therefore function very efficiently if taken up by bacteria as a result of horizontal gene transfer.

Once the Bt10 maize incident has been dealt with, we feel there should be a review of the general question of horizontal gene transfer from GMOs. There is no reason to believe that any health implications are confined to antibiotic-resistance marker genes; they could, for example, equally apply to the inserted Bt toxin genes present in all genetically modified Bt crops. However, the transfer of antibiotic resistance is the only such risk currently being addressed by the authorities that regulate GMOs.

We consider that the case-by-case approval approach used by the authorities does not adequately address such problems, which are common to all GMOs.

Gundula Azeez
Soil Association, 40-56 Victoria Street, Bristol BS1 6BY, UK