New Zealand researchers have found the active ingredients in common weed-killers can cause bacteria to be less susceptible to antibiotics, according to just published research.

The University of Canterbury, research published in Microbiology in World Antibiotic Awareness Week, built on 2015 research which found three common herbicides – including Roundup – caused E.coli and Salmonella to become less sensitive to antibiotics. The follow-up research found that active ingredients in the common weed killers – plus two surfactants used commonly in some herbicides and emulsifiers icecream ­­­­­– can cause antibiotic resistance.

Jack Heinemann, Molecular and Genetics Professor at the University of Canterbury, said the key findings of the follow-up research was that the active ingredients of Roundup, Kamba and 2,4-D, each alone could cause antibiotic resistance, and at concentrations a lot lower than the application rates on the weedkiller’s label.

Heinemann said the three herbicides were among the most common manufactured chemical products to which people, pets and livestock in both rural and urban environments were exposed.

“These products are sold in the local hardware store and may be used without training, and there are no controls that prevent children and pets from being exposed in home gardens or parks,” he said. “Despite their ubiquitous use, this University of Canterbury research is the first in the world to demonstrate that herbicides may be undermining the use of a fundamental medicine-antibiotics.”

It also found that surfuctants Tween80 and CMC that are commonly used in some herbicide formulations – and as emulsifiers in medicines and foods like icecream – can also cause antibiotic resistance at concentratations allowed in food and food-grade products.

Heinemann recommended that regulators should consider the sub-lethal effects of industrially-manufactured chemicals on bacteria when deciding whether products were safe for their intended use.

“More emphasis needs to be placed on antibiotic stewardship compared to new antibiotic discovery. Otherwise, new drugs will fail rapidly and be lost to humanity.”

Dr Siouxsie Wiles, a University of Auckland microbiologist and senior lecturer, said the paper was timely in Antibiotic Awareness week and showed how complex the microbial world was, as some of the ingredients made the bacteria more sensitive to some antibiotics, and others made them less sensitive.

“For me, their most striking finding was that surfactants, which are inert ingredients commonly used in all sorts of products, also increased resistance of the bacteria to various antibiotics,” said Wiles. “This means that it’s likely that many of the products we routinely use in our environment, our homes and on our bodies, may be contributing to making some bacteria more difficult to treat with antibiotics. With the crisis we are facing, that’s a real worry.”

Dr Heather Hendrickson, senior molecular bioscience lecturer at Massey University, said the scientific results of the two studies were not simple but were important because they involved clinically-relevant antibiotics and widely used herbicides that currently had little regulation on their use.

“The message from the paper is clear, we need to reconsider our use of herbicides in light of the effect that they are having on the microbial world.”




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