Commonly Used Herbicides are Making Bacteria more Resistant to Antibiotics, Researchers say

The herbicide Roundup contains chemicals that could speed up the resistance, according to the study. JOSH EDELSON/AFP/GETTY IMAGES

Commonly used herbicides can make bacteria develop antibiotic resistance significantly faster.

Researchers at New Zealand's University of Canterbury and Lincoln University looked into how herbicides that are used on a mass industrial scale affect bacteria in the latest research pointing to a harmful connection. Published in PeerJ on Friday, the study revealed the speed of antibiotic resistance and how easily it can happen.

"Herbicides are among the most widely used and dispersed manufactured products on Earth. Some form of exposure for people, pets and livestock can be routinely expected," Jack Heinemann, professor at the University of Canterbury and author on the paper, told Newsweek. "Meanwhile, antibiotics are used at high rates particularly on people, pets and livestock. Therefore, the combination of exposures for bacteria that live on us is all but guaranteed."

Heinemann and his team have researched this before and published papers in 2015 and 2017 showing the link between antibiotic resistance and herbicides. This paper's new findings are that even when herbicides make bacteria weaker or stronger, it still develops resistance, and when the chemicals in herbicides are combined with antibiotics, the rate of antibiotic resistance increase because the genetic makeup in the bacteria changes.

"That is why we call the herbicides gasoline for a fire," Heinemann explained. Antibiotics don't stay where we use them—they spread through feces, urine, and drains. As the antibiotics travel away, they encounter bacteria that could become resistant to them. The use of herbicides is only growing the areas that the antibiotics might meet these potentially-resistant bacteria.

"However, we were surprised at how powerful these formulations were for boosting resistance in populations of bacteria, and at how low the concentration of herbicide could be for this to happen. The concentrations we tested were well below application levels," Heinemann said.

The researchers studied multiple bacteria including Salmonella and E. coli. E. coli accounts for 17.3 percent of clinical infections requiring hospitalization, according to the Broad Institute. In some cases they tested, resistance evolved 100,000 faster when exposed to herbicides like Roundup, made with glyphosate or Kamba, made with dicamba. The scientists don't know yet if these reactions are directly affecting our ability to treat illnesses right now, but they think it's likely.

"Even small changes in resistance can complicate, even compromise, antibiotic therapy. In many cases, therapy could fail and the reasons not be diagnosed. Effects such as we observe might explain some of those cases," Heinemann said. However, it's still possible to start working to avoid the effects.

"The first step is to acknowledge that this is an issue. Once that is done, we and others, including manufacturers of chemical products that we are routinely exposed to, can study the sub-lethal effects on bacteria," Heinemann said. "Where effects are found, proper monitoring can be done to limit effects. We think that it is time for safety regulators to begin asking for such studies from manufactures at the time that they submit their products for regulatory approval."