The use of antibiotic
resistance markers in the development of transgenic
crops has raised concerns about whether transgenic crops
will transfer their antibiotic resistance genes to soil
micro-organisms, thus causing a general increase in
the level of antibiotic resistance in the environment.
stages of the laboratory process, developers of transgenic
crops use DNA that codes for resistance to certain antibiotics,
and this DNA often becomes a permanent feature of the
final product although it serves no purpose beyond the
laboratory stage. Will transgenic foods join cattle
feedlots and chicken farms as contributors to antibiotic
resistance in the environment?
Many soil organisms have naturally occurring resistance
as a defense against other organisms that generate antibiotics.
European researchers (Smalla
et al., 1993) sampled river water, pig manure slurry,
municipal sewage sludge, and soil and reported that
nptII, the antibiotic resistance gene used most
often in transgenic plants, was present in rivers, manure,
and sewage before transgenic plants were widely grown.
Some experts believe that antibiotic resistance is
so widespread naturally that any additional contribution
from transgenic plants would be insignificant (Smalla
et al., 2000). One biotech company, Calgene, has
calculated that bacteria acquire resistance to antibiotics
through the natural mutation process far more frequently
than they acquire it by taking in pieces of foreign
|Recent studies (Osterblad
et al., 2001; Routman
et al., 1985) on the prevalence of antibiotic
resistance in the gut bacteria of wildlife indicate
that mammals (moose, deer, voles, baboons) living
in areas isolated from humans do not harbor resistant
bacteria, while mammals living in human-populated
areas do harbor such bacteria.
Photo: Alaska Division of Community and Business
The suggestion that human activities may contribute
to the occurrence of antibiotic resistance in nearby
organisms needs further study, but this effect appears
to occur independently of transgenic crops.
While the risks from antibiotic resistance genes in
transgenic plants appear to be low, steps are being
taken to reduce the risk and to phase out their use.
- The FDA recommends that developers of transgenic
crops use antibiotics that are not commonly used for
treatment of diseases in humans. Thus, if horizontal
gene transfer does occur, micro-organisms in the body
are not likely to have acquired resistance to the
antibiotics that a doctor might prescribe to fight
- Scientists are changing their development methods.
Other marker genes, such as green fluorescent protein,
or mannose (Joersbo
et al., 1998), may be able to do the job that
antibiotic resistance markers have done.
- Scientists are also experimenting with methods
for removing the antibiotic resistance genes before
the plants are released for commercial use (Dale
and Ow, 1991; Ebinuma
et al., 1997; Iamtham
and Day, 2000; Zuo
et al., 2001), so that these genes can be used
during development and then eliminated from the final
- European scientists have developed a method for
inactivating the antibiotic resistance genes in the
event that they are transferred to bacteria in the
et al., 2001). A special DNA sequence inserted
into the antibiotic resistance gene will prevent the
gene from functioning inside a bacterium. Plants are
able to snip out the special sequence to let the gene