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Study published on March 23 in Nature Microbiology indicates that drought may favor antibiotic-resistant microorganisms in soil and relates drier regions to a higher number of reported resistant pathogens by hospitals around the world.
Drought may be contributing to the rise of antibiotic-resistant superbugs, according to new research linking soil aridity to an increase in microorganisms capable of surviving the action of these medications. The study also identified the presence, in clinical pathogens, of resistance genes found in soil bacteria, which raises concerns about the effects of climate change on public health.
The senior author of the study, Dianne Newman, a biologist at Caltech, stated that the problem is not restricted to a specific region. According to her, a pathogen that arises in one part of the world can spread rapidly, making the situation concerning anywhere.
Antibiotic resistance already represents a significant public health issue. According to estimates from the World Health Organization cited in the study, in 2019 resistant pathogens directly caused 1.27 million deaths per year and contributed to another 4.95 million.
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Drought alters the balance between microorganisms in soil
The researchers started from the observation that antibiotics used in medicine originate from microorganisms or fungi, which produce these substances as part of an evolutionary competition with other organisms. One of the main environments for this competition is the soil, where different microbes coexist, compete, and develop attack and defense mechanisms.
Newman and postdoctoral researcher Xiaoyu Shan identified an initial indication of the relationship between drought and resistance by analyzing five metagenomic databases containing genetic information from soil microbes across several continents. Some of these datasets included samples collected from the same locations before and after drought periods.
In all examined cases, genes linked to antibiotic synthesis appeared more frequently after drought and in lower quantities after the end of this period. According to Newman, this pattern was observed in agricultural areas, pastures, forests, and wetlands in countries such as the United States, China, and Switzerland.
Experiments showed increased resistance after dehydration
To understand the mechanism behind this behavior, the researchers replicated the situation in the laboratory. They treated sterile soil with phenazine, an antibiotic produced by some bacterial species, added soil bacteria, and allowed half of the samples to dry for three days while keeping the other half moist.
After the simulated drought, the scientists found that the antibiotic had become more concentrated as the humidity evaporated. In this scenario, sensitive bacteria suffered from the higher concentration of the substance, while resistant bacteria began to multiply.
According to Newman, the result shows that antibiotic resistance is driven by evolutionary pressure. When drought concentrates antibiotics produced by other microbes to lethal levels, the most resistant organisms survive.
The metagenomic databases were used again to observe this competition at the genetic level. The analysis revealed that antibiotic resistance genes became more frequent during drought periods, while antibiotic synthesis genes also increased, reinforcing the hypothesis that microorganisms affected by aridity enhance their defenses in response to pressure from neighbors.
In a new phase, the researchers collected soil samples on the Caltech campus, added four different antibiotics, and dried half of the material. Once again, the dehydrated samples showed an increase in the number of antibiotic-resistant microbes.
Relationship with hospitals reinforces the global dimension of the problem
After the soil experiments, the team sought to verify whether the same pattern could be identified on a global scale. To do this, they used existing data on resistant pathogens collected from hospitals in various parts of the world and cross-referenced it with climate and weather information to measure the level of aridity around each hospital unit.
The result indicated that the drier the region, the higher the number of antibiotic-resistant pathogens reported by the hospital. According to the researchers, this association remained even after controlling for the socioeconomic status of the countries, a factor that could influence the capacity for testing and identifying microorganisms.
A final genomic analysis brought another point of concern. Many of the genes that confer antibiotic resistance in soil microbes were found to be identical in clinical pathogens already known to evade the action of these medications.
Among the organisms mentioned are Enterococcus faecium, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and species of Enterobacteria. The results were reported on March 23 in the journal Nature Microbiology.
According to Newman, human pathogens and soil microorganisms come into contact all the time as people move through the environment. In this context, the resistance induced by drought in soil can easily be transferred to microbes present in the human body.
Climate change expands the alert about superbugs
In an editorial accompanying the study, microbial ecologist Timothy Ghaly from Macquarie University in Australia wrote that ongoing warming and persistent drought should expand arid conditions. For him, this means that climate change may accelerate a problem that is already serious: the rise of antibiotic-resistant pathogens.
Newman stated that there are ways to respond to this scenario. In addition to containing climate change, she advocated for the expansion of rapid diagnostic testing in clinics so that doctors can identify resistant bacteria earlier and define treatment more quickly.
The researcher also mentioned the possibility of using combinations of antibiotics to eliminate resistant strains.
Another point she considered crucial is the funding of basic research aimed at discovering new medications.
According to Newman, pharmaceutical companies have largely stopped investing in the search for new antibiotics due to lack of profitability. As a result, scientists associated with governments and universities have taken the lead in basic research in this area.
Commenting on this scenario, she stated that this is not the time for governments to stop funding scientific research and drug discovery. The assessment presented in the study is that, with the expansion of drought and warming, the risk of strengthening resistant bacteria tends to become even more relevant.
Study available in Nature Microbiology.
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