Ag Chemicals and antibiotic resistance

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Ag Chemicals and antibiotic resistance

Dec 5, 2017 | 19:55 1 Lengthy but interesting read from NZ.

Herbicide risk to resistance linked
by Richard Rennie

Professor Jack Heinemann has been unlocking the secret codes allowing herbicides to make bacteria resistant to antibiotics.
Amid dire warnings of a post-antibiotic apocalypse, scientists, including Dr Jack Heinemann from Canterbury University, have added an extra note of urgency. He told Richard Rennie about an unholy alliance of prolific herbicides and their contribution to antibiotic resistance.
USE of common herbicides is allowing bacteria to become resistant to antibiotics used in both human and animal health, molecular biologist and geneticist Professor Jack Heinemann
His research group raised the spectre of antibiotic resistance developing through herbicide exposure in a 2015 study.
He then looked at how bacteria responded to herbicides and how they developed the resistance.
The research focused on herbicides dicamba, 2,4-D and glyphosate and how relatively common bacteria Salmonella enterica and E coli behaved when exposed to them.
His aim was to identify what actives in herbicides were creating the resistance.
Heinemann’s original interest in the link began when he noticed the chemical structure of dicamba herbicide resembled a salicylate chemical similar to those found in compounds used in human medicines, including aspirin.
“I recalled work in the 1980s about how acetylsalicylic acid caused multiple drug resistance in bacteria.
“This prompted us to test if herbicides would also cause drug resistance – 2,4-D and dicamba are part of the same family, with the same pattern of resistance.
“We really only brought in glyphosate to use as a control.
“It does not look anything like the structure of 2,4-D and dicamba but we found it, too, prompted resistance development.”
The role of herbicides in promoting antibiotic resistance had been below the radar for legislators more concerned about the more direct human health impacts of spray exposure, such as any carcinogenic effects.
But Heinemann said the sub-lethal role herbicides might play in creating more antibiotic-resistant bacteria demanded more global attention as the world grappled with antibiotic resistance.
The work highlighted how the resistance developed through mechanisms known as efflux pumps.
Bacteria, when exposed to the herbicide, produced more of the pumps, making them less susceptible to antibiotics.
The pumps worked by responding when toxins flowed into a cell and pushing the toxins back out – both the antibiotics and herbicides were regarded as toxins by the bacteria cell, effectively vaccinating the bacteria against the toxic antibiotics and herbicides.
The work found the different herbicide actives created resistance to a range of antibiotic treatments.
Glyphosate, the active in Roundup made salmonella and E coli more resistant to two classes of drugs. One of them was ciprofloxacin, used to combat common bladder and urinary tract infections.
Exposure to the dicamba active used in Kamba broadleaf spray also made the bacteria more resistant to various antibiotics, including ciprofloxacin, tetracycline and chloramphenicol.
Heinemann said the level of direct exposure to sprays needed to cause resistance was higher than the legal safe limits in foods.
“However, it was the exposures that occurred during spraying that could reach concentrations high enough for bacteria to develop antibiotic resistance and then they could be transferred to us, such as by ingestion of bacteria from livestock that had grazed pasture treated with the herbicide actives.
“We have no withholding period on some of these products.
“Imagine that livestock on antibiotics are grazed on herbicide treated pasture.
“Nearly 80% of the administered antibiotic is not metabolised so it comes out in the manure.
“Bacteria have been exposed to both herbicide and antibiotic. Flies may then spread the bacteria.
“There are all sorts of pathways of exposure due to the use of both antibiotics and the herbicides.”
All three actives were found to contribute equally to resistance development.
“We were recording survival of bacteria at dose six times higher than normally would kill them, two times higher than is usually enough to undermine treatment therapy.”
The results were yet another blow to glyphosate, one of the world’s most ubiquitous weed killers.
The claim glyphosate was a carcinogen had moved up a level with California becoming the first state in the United States to declare it a known human carcinogen, prompted by the World Health Organisations finding it was a probable carcinogen.
However, in the European Union there had been a bitter divide over the toxicity of glyphosate and its cancer link.
Heinemann’s research also found surfactants used in herbicides to increase penetration also prompted antibiotic resistance and they had no limits on their concentration when used.
The study could not tell what proportion the herbicide link contributed to total antibiotic resistance.
However, he believed it was becoming increasingly important to better understand the link between microbes, commercially made chemicals and resistance given 700,000 people died each year because of drug resistant infections.
That was expected to rise to 10 million by 2050 if nothing was done.
“I would think New Zealand would want to at least look at this work.
“This is not just a rural issue.
“These products are used widely in both urban and rural environments and can be just bought off the shelf.” Reply With Quote
Dec 5, 2017 | 23:34 2 Thanks for posting. Interesting read.

So many products we use everyday in the modern world that are tested to ensure they aren't acutely toxic, and don't cause cancer, so therefore must be safe. But when one considers the infinite number of permutations and combinations of products which may interact, underlying conditions and genetics people may have, environmental factors etc, and the impossibility of ever testing them all, it will certainly take generations if ever to discover that a supposedly innocuous substance was causing health problems in an unlikely method.

My take away:

1) yet another reason not to abuse these valuable tools. There is an entire industry trying to take them away from us, most are delusional, but some, such as these researchers may have valid arguments.
2) To all the pessimists who think that overproduction and cheap prices are here to stay, there will be black swan events, of which this may well prove to be one, which will critically affect our ability to produce plentiful cheap and SAFE food. Reply With Quote