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It seems antibiotics and herbicides don't mix.
The worrying finding is that, while the presence of a herbicide might increase the effectiveness of an antibiotic, most often it reduces it. Impaired antibiotic effects of up to three-fold were observed.
This has serious implications for the therapeutic value of the drugs. But also, by creating a situation where the pathogens survive normally lethal treatments, the scene is set for antibiotic resistance to evolve in dangerous infectious diseases.
In the US alone
"more than two million people are sickened every year with antibiotic-resistant infections, with at least 23,000 dying as a result. The estimates are based on conservative assumptions and are likely minimum estimates." (US Center for Disease Control)Exactly how the herbicides interfere with antibiotic activity isn't clear, but because the effect is immediate, the authors suspect there are direct biophysical effects on the bacterial membrane which prevent the drug entering. This raises the possibility that the so-called 'inert' ingredients put into herbicide formulations to enable the plant-killing chemical to penetrate through the cell membrane might be to blame.
Even Monsanto admits that herbicide formulation additives are known to have an effect on cultured microbes and that it's difficult to separate the 'active' from the 'inert' ingredients.
It was pointed out by the New Zealand scientists that, while transient effects on the bacterial membrane which block antibiotic action represent only a short-term problem, they nevertheless increase the possibility of heritable antibiotic-resistance mutations in the pathogens.
The study tested two different potentially pathogenic bacteria and five common classes of antibiotic. It demonstrated, above all, that interactions in a system containing a variety of bugs, a variety of antibiotics and a variety of herbicides, are going to be unpredictable: they vary with bacterial strain, the specific antibiotic and the brand of herbicide. The permutations are infinite, but combinations with a lethal outcome for some vulnerable people are certain.
Even more concerning, is that it seems the negative herbicide-effects on antibiotic action are additive, and other drugs and chemicals such as salicylic acid can also contribute.
Concentrations of the three herbicide formulations used in the experiment were higher than those permitted in food and feed. However, the evident complexity and additive nature of the weed-killer/antibiotic/pathogen interactions doesn't rule out the possibility of unpredictable facilitation of disease even at low exposures.
Since the herbicide levels used were well within those to which agri-workers are exposed, this sector of the population is likely to become a source and reservoir of antibiotic-resistant bugs.
Also, because the use of these three weedkillers in homes and gardens can't be tightly regulated, gardeners and their pets and children are clearly at increase risk of developing untreatable infectious diseases.
The bigger picture is that antibiotic-resistance may also be boosted by horizontal gene transfer of the artificial antibiotic-resistance marker genes commonly inserted into GM animal feed. Although the danger in the use of such marker genes has been recognised since GM day-1, antibiotic-resistance marker genes are still widely present: the Norwegian government recently banned eight of nineteen GMOs used in fish feed due to the presence of these genes. And, of course, antibiotics continue to be routinely used in intensively-reared livestock fed GM feed.
To cap it all, the EU has just handed out seventeen authorisations or re-authorisations for GM food crop import and use: eight of these have tolerance to glyphosate, one has tolerance to dicamba and two have tolerance to glufosinate which hasn't been tested but might well be as bad as all the rest. America has just approved GM crops with tolerance to 2,4-D. And thanks to the modern superweed-filled fields, multi-herbicide-resistant GM crops are now all the rage in the world of biotech.
There's certainly an unhealthy scope in that lot for additive negative effects brewing in livestock, in the soil and inside you.
The answer to the antibiotic resistance problem would seem to lie in rearing our livestock in healthy (extensive) conditions, on a healthy (non-GM) diet so that they aren't so exposed to the offending herbicides or to the offending genes and don't have to be plied with drugs to keep them 'fit' for the table.
Is it likely that the cost of sickness, disease and death is less than the cost of converting our food supply to something more natural?
- Brigittta Kurenbach, et al., 2015, Sublethal Exposure to Commercial Formulations of the Herbicides Dicamba, 2,4-Dichlorophenoxyacetic Acid, and Glyphosate Cause Changes in Antibiotic Susceptability in Escherichia coli and Salmonella Enterica seroval Typhimurium, mbio.asm.org, March/April 6:2
- Amy Westervelt, Common pesticides linked to antibiotic resistance, Guardian 24.03.15
- Herbicides used with GM crops alter antibiotic resistance of disease-causing bacteia, GM Watch 23.03.15
- Commission authorises 17 GMOs for food/feed uses and 2 GM carnations, European Commission Press release 24.04.15
- Kacey Birchmeier, Enlist Duo Receives EPA Approval in Additional States, www.agriculture.com, 1.04.15
- Norwegian food authority stops approving antibiotic marker gene-containing GMOs in fish feed, GM Watch 28.11.14