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Herbicides Have a Dangerous Side Effect: Bacteria Antibiotic Resistance

A new scientific study has demonstrated that three of the most common herbicides are causing bacteria to develop increased resistance to antibiotics. This is really bad.

Hand with IV in hospital

Antibiotic resistance is one of the biggest threats to human health.

The University of Canterbury, New Zealand, research project found that the active ingredients in three of the most commonly used herbicides in the world, shipped under the brand names Roundup, Kamba and 2,4-D, have been proven to trigger antibiotic resistance in bacteria. And this happens even at application levels below the maximum safe recommended concentrations for these herbicides.

The active ingredients in the three herbicides – glyphosate, dicamba and 2,4-D, respectively – are already a source of major worldwide concern for other reasons. Glyphosate has been labeled a carcinogen by a number of health and regulatory agencies and has been linked to a variety of ailments, including cancers, tumors, kidney problems and more. All three herbicides are harmful to many living things, of course, since that is what they were designed to do.

With herbicides being dumped on the world in larger quantities every year, this latest study result is a very serious concern on an entirely new level.

The research paper published online in Microbiology in November 2017 reported that the study looked at bacteria such as Salmonella enterica and Escherichia coli (E. coli), both common and highly toxic pathogens for the human body, and how they are impacted by exposure to the herbicides. Specifically, the researchers were studying what is referred to as the minimum inhibitory concentration (MIC) of antibiotics required to treat them properly.

As noted in the study, bacteria have what are known as adaptive responses, which increase their antibiotic resistance in the presence of certain kinds of triggers. Wrong combinations of antibiotics; substances like salicylic acid, which simply seem to cause a response; bile salts; and even stresses from changes in pH have been proven to be triggers for certain bacteria.

This is a complementary but different antibiotic resistance response than two other categories of concern for the growth of antibiotic resistant pathogens. One of those categories has to do with the widespread use of antibiotics everywhere – from human treatment to livestock and feed – resulting in an antibiotic overload that, in turn, causes adaptive responses in bacteria to fight off those treatments. The second category includes areas polluted from runoffs from various contaminations associated with antibiotics, especially agricultural and livestock-raising areas where antibiotics are also used.

Herbicides themselves are in reality a complex mix of chemicals, with the active ingredients being the poisons and the inactive ingredients having a number of different functions, such as the surfactants that act to make it easier for the active ingredients to penetrate into their intended targets. These inactive ingredients are referred to by the U.S. Environmental Protection Agency as co-formulants and are defined as “other than an active ingredient that is intentionally intended in a pesticide product.”

The study looked at the herbicides themselves as well as the isolated toxic agents and co-formulants to determine all the items that might be contributing to the antibiotic trigger factor. For the herbicide formulations, the researchers looked at the active ingredients dicamba (3, 6-dichloro-2-methoxybenzoic acid), 2,4-D (2,4-Dichlorophenoxyacetic acid) and glyphosate (N-(phosphonomethyl)glycine). For the co-formulants, the focus was on Tween80 and carboxymethyl cellulose (CMC), two commonly used surfactant compounds the researchers found on patent applications for the herbicides. Tween80 tends to break down the surface tension on water so the herbicides can distribute better on leaf surfaces. CMC acts as a binding agent and regulates viscosity of the herbicide.

In the tests, the researchers examined a variety of antibiotic concentrations and conducted multiple runs to verify the results.
The final results exhibited not only that 2,4-D and dicamba showed major increases in antibiotic resistance but also that exposure to glyphosate showed “statistically significant increases” in resistance from treatment by ampicillin, ciprofloxacin and kanamycin, three commonly prescribed antibiotics for the Salmonella enterica and E. coli bacteria under investigation.

For the surfactants, the results showed that Salmonella enterica was triggered most by CMC, with respect to kanamycin treatment, and by Tween80 with respect to chloramphenicol. E. coli resistance was strongest after a trigger by Tween80, with respect to kanamycin, and strongest after a trigger by CMC with respect to ampicillin.

With herbicides in increasing use all over the world and products like glyphosate-based Roundup tied to Monsanto’s GMO product lines (which are gaining market share worldwide), the risk of increased bacterial resistance to antibiotics – because of herbicide runoff and contamination in our water systems – is and apparently has been getting worse for some time.

Herbicides are not the only fear here. As the researchers report in their paper, chemicals called polysorbates, very commonly used as solubilizing agents in products used for “chronic human exposures,” have also been found to be triggers to increased antibiotic resistance in bacteria. Polysorbates are a virtual staple of cosmetics, mouthwash and a variety of medical preparations.

The combined over-prescribing of antibiotics for human treatment (a chronic problem for decades) and overuse of antibiotics in meat and poultry and their feed products has already produced an “overdose” of antibiotics and the rise of what some have called superbugs. And acquired antibiotic resistance will get even worse globally due to constant exposure to non-antibiotic triggers such as herbicides, their co-formulants mentioned within this particular piece of research, polysorbates and likely many other chemicals that are yet to be discovered for their impact as triggers.

Dealing with the problem would require an orchestrated response by the medical industry, agribusiness and government, which is not going to happen in most countries. Such a respond could include the cyclical de-introduction of certain antibiotics, followed by re-introduction afterwards, to keep them from being around so long that their continuous presence forces bacterial adaptation. It will also now have to include some consideration of herbicide regulation. Herbicide overuse is already well-known as a factor behind why entire agricultural land ecosystems have been compromised over the past 30 years and why those of us driving along superhighways through those regions may have noticed far fewer bugs on our windshields than when we were younger. With the additional problem that all of these herbicides are likely causing to the bacteria environment (as triggers to cause bacteria to adapt to be resistant to antibiotics), there is now an even bigger reason for some action to be taken – and fast. But action won't be taken, so now is a good time to prepare for a world with increasingly fewer options to treat bacterial infections.

Effective alternatives to pharmaceutical antibiotics include citrus seed extract, hydrogen peroxide (H2O2) and silver.