More Information on Impacts of HGT from Biotech Crops

In an evaluation of potential transfer of a kanamycin resistance gene from biotech plants into enteric bacteria, scientists established one new kanamycin-resistant cell would be produced for every 750 billion already present in the gastro intestinal tract. They point out that 75-86% of human enteric bacteria, such as Streptococcus are already resistant to this antibiotic. Therefore, they estimate the transformation frequency of enteric bacteria would be approximately five orders of magnitude less than the frequency of natural mutation to antibiotic resistance for these organisms.

Some have argued that HGT from plants to bacteria is expected to be higher in biotech plants containing integrated plasmid, as demonstrated experimentally under artificial conditions using marker-rescue transformation. However, scientists believe the probability of an antibiotic resistant gene in plants moving via horizontal transfer to microorganisms is negligible. Agrobacterium and the particle gun are the most frequently used vectors to transform plants. With particle gun transformation, only the expression cassette (no plasmid) is integrated, while in Agrobacterium, only the expression cassette and T-DNA border sequences are integrated. In both cases, the integrated DNA is isolated from the original plasmid transformation vector and does not have the sequences required for autonomous replication or “shuttling”.

Also, as described above, if HGT of antibiotic resistance marker genes were to occur, the consequence of such an event would be negligible inasmuch as these genes are already prevalent in populations of enteric bacteria. Therefore, the presence of antibiotic resistance markers in plant are unlikely to increase the prevalence of antibiotic resistant pathogens, and the ultimate impact of the highly improbable occurrence of HGT of antibiotic resistance marker genes from plants to other organisms is virtually zero.