Crop sprayer

Health Impact News Editor Comments

A 2015 study was published looking at the effects of three widely used herbicides on disease-causing bacteria and their susceptibility to antibiotics. The three herbicides are dicamba, 2,4-D (recently approved by the U.S. EPA), and glyphosate. In what is believed to be the first study of its kind, they researches found that these popular herbicides affected the bacteria responded to antibiotics, often developing a resistance to them.

GM Watch conducted an interview with some of the study’s authors.

GMW: What did you find?

Heinemann: When we exposed either of two different species of bacteria to common herbicides that we purchased at a local store, we found that the bacteria changed their response to antibiotics. They often became antibiotic resistant, but we also occasionally saw increased susceptibility or no effect.

GMW: Which herbicides and antibiotics are you talking about?

Kurenbach: We tested commercial formulations of herbicides based on the active ingredients dicamba, 2,4-D and glyphosate. The antibiotics were representative of five major groups: β-lactams (ampicillin), chloramphenicol, tetracycline, fluroquinolones (ciprofloxacin) and aminoglycosides (kanamycin).

GMW: Why does your study matter?

Heinemann: Every day you see in the news that there are concerns about the ever increasing frequency of antibiotic resistance in bacteria that can cause disease in people and our animals. Anything that contributes to this problem should be considered because new antibiotics are rare.

Kurenbach: The effects found may be relevant if people or animals are exposed to herbicides at the higher ranges of concentration, those that occur when it is applied rather than what is normally found on food. Those kinds of exposures may be experienced by, for example, farm animals and pollinators in rural areas and potentially children and pets in urban areas.

Heinemann: And we can’t predict either the direction or size of the observed effects based on bacterial species, antibiotic or herbicide used. Thus, different potential disease-causing bacteria may react differently to the same herbicide or to the same antibiotic.

GMW: Is this the first study to show this?

Kurenbach: We’ve looked hard to find other studies like this, but haven’t found any. Other studies have reported on other substances that also change bacteria’s tolerance to antibiotics (e.g. aspirin), but herbicides weren’t used.

GMW: What are the limitations of your study?

Heinemann: While we tested examples from most major groups of antibiotics, there are more individual antibiotics than we could test. And our tests are in the laboratory. We hope to get funding to test environmental samples or bacteria from animals.

Kurenbach: We only tested two species of bacteria. They were laboratory strains of disease-causing species. We’d like to test the response of more species of bacteria.

We provide genetic and biochemical evidence of how the bacteria become resistant or sensitive. But there may be more ways than we have so far described.

GMW: Have these results been replicated?

Heinemann: As part of this study we engaged another scientist at another university in a blinded replication. We sent her the bacteria and chemicals through an intermediary who kept their identities a secret. Using our protocols, she was able to confirm our findings. She also later joined the author team.

Read the full article here.


Sublethal Exposure to Commercial Formulations of the Herbicides Dicamba, 2,4-Dichlorophenoxyacetic Acid, and Glyphosate Cause Changes in Antibiotic Susceptibility in Escherichia coli and Salmonella enterica serovar Typhimurium – Brigitta Kurenbacha, Delphine Marjoshia, Carlos F. Amábile-Cuevasb, Gayle C. Fergusonc, William Godsoed, Paddy Gibsona, Jack A. Heinemanna – American Society for Microbiology – doi: 10.1128/mBio.00009-15 24 March 2015 mBio vol. 6 no. 2 e00009-15 (abstract)



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