29
May
Antibiotic-Resistance Genes Rise with Pesticide Application, as Study Adds to a Plethora of Findings
(Beyond Pesticides, May 29, 2024) A study from the Academy of Biology and Biotechnologies and the Federal Rostov Agricultural Research Centre adds to the body of science linking pesticide use with negative impacts on soil health and bacterial communities. Antibiotic-resistance genes (ARGs), considered a class of pollutants, are found in certain types of bacteria and can spread through the environment and subsequently to humans and animals. This study, performed by researchers and soil experts, found an increase in specific bacterial families that host ARGs with exposure to pesticides.Â
The study aims to identify the role of agricultural soils in ARG transfer and to assess the presence and prevalence of bacterial families with and without exposure to fertilizers and pesticides. Since soil serves as a habitat for a wide range of bacteria, including many that are resistant to antibiotics, analyzing the organisms within soil samples is an indicator of overall environmental health. Agricultural soils are essential in food production, and as this study states, “[I]ntensive exploitation of such soils implies the widespread use of various chemical plant protection products (insecticides, herbicides, fungicides) and mineral fertilizers, which contribute to pollution and a decrease in soil quality.â€Â Â
Within this field study, there is a control group to compare against a group treated only with mineral fertilizers, a group treated only with pesticides, and a group treated with a combination of the fertilizers and pesticides. The experiment was conducted in the Rostov region of Russia on soy and sunflower crops grown in plots during 2022 and then on wheat grown in the same plots the following year. Soil sampling was conducted before and after exposure to the fertilizers and pesticides, and rRNA gene sequencing and quantitative real-time PCR were performed to study the soil microorganisms and to determine the bacterial community taxonomy and ARGs present in the bacteria.    Â
Overall, the soil bacteria community structure is similar in all studied samples, with common families of bacteria present. While the “agrochemical treatments had little effect on changes in the abundance of individual bacterial taxa,†the number of bacteria within families or genera increased or decreased with the application of fertilizers, pesticides, and the combined treatment. Most notably, the study found that “the abundance of certain taxa (Sphingomonadales, Gemmataceae, Burkholderiaceae) was significantly increased in soils treated with pesticides.†Species within these families of bacteria are known for high antibiotic resistance (studies here, here, and here).Â
Resistance within bacteria can rapidly spread to neighboring bacteria through horizontal gene transfer. The resistance becomes no longer tied to a specific species but can then persist in the larger microbial environment. Stressors within the system, such as pesticides, contribute to the evolution of bacterial antibiotic resistance and horizontal gene transfer. Application of pesticides induces acquired antibiotic resistance via several pathways; mechanisms for this include the “activation of efflux pumps, inhibition of outer membrane pores for resistance to antibiotics, and gene mutation induction.â€Â
Chemical-intensive agricultural practices, which rely heavily on synthetic fertilizers and pesticides, contribute to poor soil health and ecological destruction which, since soil serves as a natural reservoir for many ARGs, leads to higher resistance. As the researchers found, even “sublethal concentrations of pesticides can provoke oxidative stress and enhance mutagenesis in bacteria, which cause changes in antibacterial defense enzymes, among others. Pesticides can also affect the soil bacterial community, reducing diversity and shaping a specific community of bacteria, including promoting ARG hosts.â€Â
Additional studies suggest that pesticides drive resistance within soil microbiomes. Soils exposed to weed killers contain a greater abundance of ARGs, even at exceptionally low levels, demonstrating that pesticides can “significantly change the genetic composition of soil bacterial populations.†Moreover, another finds that “bacteria exposed to widely used herbicides like Roundup develop antibiotic resistance 100,000 times faster than average.â€Â Â
There is a history of pesticide usage that correlates with higher antibiotic resistance. For example, a common species of bacteria, Escherichia coli, becomes stimulated toward higher resistance when exposed to pesticides. Genetic mutation occurs as a result of the application of pesticides, leaving behind more resistant bacteria that can spread throughout the environment. The research indicates that this resistance develops directly in the field, with soils sprayed with pesticides likely to contain higher amounts of antibiotic resistant bacteria that then transfers to other organisms. Â
As Beyond Pesticides has previously written about, in 2019 the University of Washington’s Institute of Health Metrics and Evaluation reported that millions of people died as a result of resistance. The statistics state that “4.95 million people who died in 2019 suffered from drug-resistant infections, such as lower respiratory, bloodstream, and intra-abdominal infections†and “1.27 million deaths in 2019 were directly caused by AMR [antimicrobial resistance].â€Â
U.S. Environmental Protection Agency (EPA) inaction, despite sponsoring research that confirms the spread of antibiotic resistance to humans from horizontal gene transfer in the environment, only adds to the problem. As drug-resistance has been documented as being on the rise for years, EPA’s response, or lack thereof, has been increasingly apparent. In one case, as previously reported by Beyond Pesticides, “The agency failed to assess the efficacy of any pesticides that are not used for public health purposes; EPA only evaluated the efficacy of antimicrobial compounds whose use patterns classify them as human-health-related—thus ignoring the impact of other antimicrobial pesticides on resistance in human pathogens.â€Â Â
The courts have not followed the science on horizontal gene transfer and the damaging effects of antibiotic resistance on public health. The courts have ignored the World Health Organization’s warning of a looming pandemic associated with antibiotic resistance and instead deferred to EPA’s inaction. In a lawsuit from December 2023 filed against the expanded use of streptomycin in citrus production for Huanglongbing, also known as “citrus greening†(a plant disease spread by the Asian citrus psyllid), the Ninth Circuit Court of Appeals found that since “EPA emphasized that ‘there is no data that antibiotic use in agriculture leads to the presence of antibiotic resistance in bacteria of human health concern†that “[a]t the present time, there is little evidence for or against the presence of microbes of human health concern in the plant agricultural environment.†And yet on May 19, 2019, The New York Times reported, “The agency approved the expanded use [of streptomycin] despite strenuous objections from the Food and Drug Administration and the Centers for Disease Control and Prevention, which warn that the heavy use of antimicrobial drugs in agriculture could spur germs to mutate so they become resistant to the drugs, threatening the lives of millions of people.†(See the following opportunity to take action on antibiotic resistance.)Â
The court, in Migrant Clinicians Network, Beyond Pesticides et al. v. EPA (represented by Earthjustice), did find EPA’s action to allow expanded streptomycin use illegal for other reasons, ruling that the agency failed to reach findings on the impacts on bees and the agency’s responsibility for evaluation under the Endangered Species Act.Â
Despite litigation and copious studies, there is a growing crisis in health care due to drastic increases in antibiotic resistance. Non-organic agricultural practices, which utilize antibiotics in crop and livestock production, exacerbate this major health issue by also applying harmful pesticides that promote ARGs in bacteria. Despite resistance on many farms that have led to harm and collapse, there are organic methods that offer a path forward. The foundation of all organic systems starts in the soil, which highlights the importance of promoting healthy soil and the microorganisms within it.Â
Make The Safer Choice to avoid hazardous home, garden, community, and food use pesticides and learn about organic agriculture. There are direct health benefits of going organic and supporting organic, and these methods also reduce the threat of the climate crisis. Voice your concern and help to keep organics strong.     Â
All unattributed positions and opinions in this piece are those of Beyond Pesticides. Â
Source:Â
Khmelevtsova, L. et al. (2024) Effect of mineral fertilizers and pesticides application on bacterial community and antibiotic-resistance genes distribution in agricultural soils, Agronomy. Available at: https://www.mdpi.com/2073-4395/14/5/1021.Â
