A study published late last month in the journal Scientific Reports is the latest to link commonly used herbicides to the rise of antibiotic-resistant bacteria.
This is the latest finding connecting commonly used herbicides to the rise of antibiotic-resistant bacteria, with prior research showing glyphosate, 2,4-D and dicamba are able to create resistance in Salmonella and E. coli.
While federal regulatory agencies continue to ignore the role of pesticides in the development of antibiotic resistance, it is critical for states and localities to take action to protect their most vulnerable both from toxic exposure to these herbicides and the multitude of indirect effects caused by their use.
This is all happening as antibiotic resistance is rising to dangerously high levels in all parts of the world, according to the World Health Organization.
In the May 1 issue of the Bulletin of the World Health Organization, Samira Choudhury, Ph.D., et al. write, “Often referred to as the silent pandemic, antimicrobial resistance claims the lives of over 700,000 people annually.”
The authors continue, “A study suggests that if no actions are taken, antimicrobial resistance will cause 10 million deaths per year by 2050 and an economic impact of over 100 trillion United States dollars.”
Scientists focus their research on Pseudomonas aeruginosa, a bacteria commonly found in the environment, but able to cause serious disease in humans. Healthy people can be infected from improperly cleaned hot tubs or swimming pools, resulting in skin rashes and eye and ear infections.
However, the greatest risk of P. aeruginosa is in the hospital setting. The bacteria is well known to infect those suffering from burn wounds, on a ventilator or other invasive medical device and/or with a catheter. Hospital-acquired P. aeruginosa is deadly in large part due to the wide spectrum of multi-drug antibiotic resistance the bacteria possess.
The Centers for Disease Control and Prevention indicates that in 2017 32,600 Americans hospitalized came down with a P. aeruginosa infection, with 2,700 passing away as a result.
To better understand the role pesticides like glyphosate are playing in these deadly infections, scientists examined five different strains of P. aeruginosa, four retrieved from the environment and one from a clinical setting. All represented strains that were initially sensitive to antibiotics.
These strains were exposed to both technical grade glyphosate and a range of glyphosate-based herbicide (GBH) formulations, including the products Roundup Mega, Dominator Extra 608 SL and Gladiator 480 SL (which are sold only in Europe).
P. aeruginosa was exposed to 0.5% of glyphosate and GBH products per the volume of the medium (equivalent to 1.8-2.8 g/L [glyphosate] acid depending on the type of formulation).
“This concentration falls within the recommended dilution range of GBHs [0.2-3.5% (v/v)] for agricultural and household use and similar to those found in water after agricultural practices,” the study notes.
At this level, glyphosate and its formulated products significantly increase the minimum inhibitory concentration (the lowest concentration of an antibiotic that would inhibit the growth of a given bacteria) of P. aeruginosa to the carbapenem-type antibiotic imipenem by between 2-32 fold. This occurred in all strains and under different exposure scenarios.
“Considering the worldwide use of [glyphosate] and GBHs, and the simultaneous emergence of antibiotic-resistant bacteria in environmental matrices, the detected interactions between these chemicals may affect microbial communities and possess a potential environmental and human health risk,” the authors explain.
Future studies will likely determine the mechanism through which this problem is occurring.
It is becoming increasingly evident that glyphosate is creating resistance problems in more than merely the weeds on which the chemical is being applied to control. Initial reports on glyphosate’s antibiotic resistance properties came in 2015, a week after the chemical was deemed a possible carcinogen by the World Health Organization.
Two years later these reports were confirmed in greater detail by the same team of scientists. In 2018, researchers found that bacteria exposed to glyphosate-based Roundup can develop antibiotic resistance 100,000 times faster than average.
The most recent findings indicate that this resistance is developing directly in the field, with soils sprayed with weedkillers likely to contain higher amounts of antibiotic-resistant bacteria.
The regulatory response to this near decade of research on the antibiotic resistance properties of commonly used herbicides has been nil. While the U.S. Environmental Protection Agency (EPA) requires herbicide product labels to include information on abating weed resistance, antibiotic resistance is not mentioned.
If anything, the EPA uses the phenomenon of antibiotic resistance as a comparison point to weed resistance, without any mention of the role glyphosate and other herbicides could be playing in both phenomena.
With inaction from federal regulators, it is up to states and localities to protect their residents from the rise of pesticide-induced antibiotic-resistant bacteria. P. aeruginosa is known to attack the most vulnerable at its weakest stage.
Yet, it is perfectly possible for a landscaper to be spraying glyphosate outside of the room of a patient suffering from a P. aeruginosa infection.
Despite the high level of care that doctors, nurses and custodial staff may put into deterring the spread of P. aeruginosa infections within a hospital, pesticide use outside may be resulting in patients and staff tracking in resistant bacteria, acting as a steady source of environmental exposures.
Resistant bacteria travels throughout the environment through a process called horizontal gene transfer, causing widespread resistance even if the use site of the chemical does not come into direct contact with someone suffering from or vulnerable to an infectious disease.
The human pathogenic organisms themselves do not need to be directly sprayed by the antibiotic because the movement of genes in bacteria is not solely “vertical” — that is from parent to progeny — but can be “horizontal” — from one bacterial species to another.
Stopping the use of carcinogenic, antibiotic resistance forming pesticides outside hospitals where individuals are suffering from the diseases these chemicals can cause is common sense.