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Study finds herbicides increase antibiotic resistance genes in soil
New research by scientists from China and the United Kingdom shows that three widely used herbicides increase the prevalence of antibiotic resistance genes in soil bacteria, along with the mobile genetic elements that enable those genes to move between bacteria. The research appeared yesterday in Molecular Biology and Evolution.
In a series of experiments, the scientists showed that application of the herbicides glyphosate, glufosinate, and dicamba to soil microcosms over 60 days significantly increased the total abundance of antibiotic resistance genes in soil bacteria, with glyphosate showing a ninefold increase in antibiotic resistance genes compared with control soil samples. In addition, glufosinate and glyphosate significantly increased total abundances of mobile genetic elements, with glyphosate and glufosinate having more of an impact than dicamba.
Further experiments suggest that the herbicides may promote antibiotic tolerance by changing bacterial gene expression, or by selecting for mutations that increase tolerance to antibiotics during prolonged herbicide exposure. The scientists also found that herbicide exposure increased bacterial cell membrane permeability and conjugation of multidrug-resistant plasmids, which promote the movement of antibiotic resistance genes between bacteria.
To assess whether these laboratory findings translated to real-world settings, the scientists sampled soil from 21 agricultural sites across China and compared soil exposed to glyphosate with soil that had been free of herbicide use for 5 years. They found that glyphosate application was associated with higher relative abundances of both antibiotic resistance genes and mobile genetic elements.
The authors of the study note that although the presence of antimicrobial resistance genes and mobile genetic elements in harmless soil bacteria may not pose a health threat, fertilization of fields with untreated animal manure that typically contains opportunistic pathogens could result in those bacteria acquiring resistance genes and spreading. The authors say that the effect of herbicides on soil microbiomes should be re-evaluated.
“While antibiotic resistance genes are not harmful per se, they will reduce the efficiency of antibiotics during clinical treatments,” study author Ville Friman, PhD, of the University of York, said in a university press release. “Keeping the frequency of resistance genes low will hence prolong the long-efficiency of antibiotics. As resistance genes can easily move between environments, agricultural fields could be globally important sources for resistance genes.”
Feb 16 Mol Biol Evol abstract
Feb 16 University of York press release
UK study shows sustained drop in outpatient antibiotics during pandemic
A decline in community antibiotic prescribing in North West London that began before the first COVID-19 peak in March 2020 was sustained for 8 months, UK researchers reported this week in Clinical Microbiology and Infection.
In the study, researchers from the UK National Institute for Health Research and Imperial College London analyzed individual prescribing records for 2 million people in North West London from January 2015 through November 2020 and conducted an interrupted time series analysis to determine whether there was a measurable change in antibiotic prescribing in primary care associated with the pandemic and the national response. Antibiotic prescriptions in 2020 were stratified by gender, age-group, ethnic group, and socioeconomic deprivation level, and prescribing records were linked to SARS-CoV-2 test results.
From January through November 2020, 730,001 primary care antibiotic prescriptions were identified. The interrupted time series analysis showed that the antibiotic prescribing volume in North West London had been declining before March 2020 at a rate of 584 items per month, but the rate of decline climbed to 3,504 items per month after March 2020.
The rate of decline was sustained beyond the initial peak of COVID-19 cases, with the antibiotic prescribing volume reaching its lowest level in August 2020. Reduced antibiotic prescribing continued into the second COVID-19 peak, which began in late September. The observed decline, which occurred despite primary care consultation rates returning to normal, was seen across all gender, age, ethnic, and socioeconomic groups.
From January through August 2020, prescribing of penicillins declined the most (57.2% of March levels), followed by macrolides (54.6%) and tetracyclines (45.0%). Among 6,158 COVID-19 patients, the most commonly prescribed antibiotics within 14 days of a positive test were amoxicillin (34.9%) and doxycycline (27.4%).
“The reduction in community prescribing associated with COVID-19 and the national pandemic response could potentially have a favourable impact on antimicrobial resistance,” the study authors wrote. “Our results need to be seen in the context of all antibiotic prescribing, and further monitoring is required to see whether this reduction persists and the impact that it will have.”
Feb 15 Clin Microbiol Infect study