Does GM food increase resistance of pathogenic bacteria to antibiotics?

Antibiotic resistance (AR) genes may be used in laboratories as a tool for selecting plant cells transformed by exogenous DNA. The gene of interest is physically linked to the AR gene by recombinant DNA technology and selection of the few resistant cells after DNA delivery ensures that they also contain the DNA encoding the useful trait. Such ‘selectable markers’ are commonly used by geneticists for transforming microbial cells and they have been successfully applied to plant cells. As a result, the regenerated plant and its progeny contain the AR gene, as a remnant of the technical procedure and with no more practical interest at the commercialization stage. Since antibiotics are essential to the safeguard of human and animal health and considering the pressing problem of multiple resistance developing in bacterial pathogens, concerns have been raised on the use of AR selection markers in GM plants, food and feed. Could these genes from marketed GM plants increase the frequency of antibiotic resistant pathogenic bacteria, in the short or in the long term? For defining the risk, several aspects must be taken into consideration : the therapeutic relevance of the antibiotic (based on the current and potential use), the occurrence of resistance genes in the environment (natural and human-associated habitats) ; the possibility of gene transfer from GM plant material to bacteria.  When adopting this reasoning to the only AR gene found in GM plants today (and most likely in the future) – the nptII gene conferring resistance to a range of aminoglycosides, like kanamycin and neomycin -, it may be concluded that the presence of this marker gene poses negligible risk, immediate or delayed, to human and animal health. This risk assessment was expressed in an EFSA opinion and took into account the following experimental and empirical observations:

1) DNA transfer can only be observed at extremely low rate in forced laboratory conditions (under selection pressure and with pre-existing homologous sequences in the recipient bacteria);
2) Aminoglycoside resistance genes, including nptII, are widespread in all environments, hence GM plants on the market can not contribute to significant increase of this frequency. As a conclusion of this intensely debated issue, GM plants may not be regarded as potentially contributing to bacterial resistance towards therapeutically relevant antibiotics, in the short as in the long term.

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