Her­bi­cides Have a Dan­ger­ous Side Ef­fect: Bac­te­ria An­tibi­otic Re­sis­tance

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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.

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 re­sponse 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 com-promised 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 prob-lem that all of these her­bi­cides are likely caus­ing to the bac­te­ria en­vi­ron­ment (as trig­gers to cause bacte-ria 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 op-tions to treat bac­te­rial in­fec­tions.

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